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1

Aquaporins: water channel proteins of the cell membrane  

Microsoft Academic Search

Aquaporins (AQP) are integral membrane proteins that serve as channels in the transfer of water, and in some cases, small solutes across the membrane. They are conserved in bacteria, plants, and animals. Structural analyses of the molecules have revealed the presence of a pore in the center of each aquaporin molecule. In mammalian cells, more than 10 isoforms (AQP0–AQP10) have

Kuniaki Takata; Toshiyuki Matsuzaki; Yuki Tajika

2004-01-01

2

Prediction of functional residues in water channels and related proteins.  

PubMed Central

In this paper, we present an updated classification of the ubiquitous MIP (Major Intrinsic Protein) family proteins, including 153 fully or partially sequenced members available in public databases. Presently, about 30 of these proteins have been functionally characterized, exhibiting essentially two distinct types of channel properties: (1) specific water transport by the aquaporins, and (2) small neutral solutes transport, such as glycerol by the glycerol facilitators. Sequence alignments were used to predict amino acids and motifs discriminant in channel specificity. The protein sequences were also analyzed using statistical tools (comparisons of means and correspondence analysis). Five key positions were clearly identified where the residues are specific for each functional subgroup and exhibit high dissimilar physico-chemical properties. Moreover, we have found that the putative channels for small neutral solutes clearly differ from the aquaporins by the amino acid content and the length of predicted loop regions, suggesting a substrate filter function for these loops. From these results, we propose a signature pattern for water transport.

Froger, A.; Tallur, B.; Thomas, D.; Delamarche, C.

1998-01-01

3

Carbon nanotube based artificial water channel protein: membrane perturbation and water transportation.  

PubMed

We functionalized double-walled carbon nanotubes (DWCNTs) as artificial water channel proteins. For the first time, molecular dynamics simulations show that the bilayer structure of DWCNTs is advantageous for carbon nanotube based transmembrane channels. The shielding of the amphiphilic outer layer could guarantee biocompatibility of the synthetic channel and protect the inner tube (functional part) from disturbance of the membrane environment. This novel design could promote more sophisticated nanobiodevices which could function in a bioenvironment with high biocompatibility. PMID:19245237

Liu, Bo; Li, Xiaoyi; Li, Baolei; Xu, Bingqian; Zhao, Yuliang

2009-04-01

4

Fetal development of membrane water channel proteins aquaporin-1 and aquaporin-4 in the human brain  

Microsoft Academic Search

Aquaporin-1 and aquaporin-4, water channel membrane proteins reported in both experimental animals and in adult humans, have been detected in different, non-overlapping areas of the central nervous system. This immunohistochemical study describes the developmental expression pattern of the water channel membrane proteins, aquaporin-1 and aquaporin-4, in various structures of human fetal brain over the gestational period of 14–40 weeks.Aquaporin-1 immunostaining

Éva Gömöri; József Pál; Hajnalka Ábrahám; Zsolt Vajda; Endre Sulyok; László Seress; Tamás Dóczi

2006-01-01

5

Cellular distribution of the aquaporins: A family of water channel proteins  

Microsoft Academic Search

A group of transmembrane proteins that are related to the major intrinsic protein of lens fibers (MIP26) have been named “aquaporins” to reflect their role as water channels. These proteins are located at strategic membrane sites in a variety of epithelia, most of which have well-defined physiological functions in fluid absorption or secretion. However, some aquaporins have been localized in

Dennis Brown; Toshiya Katsura; Megumi Kawashima; A. S. Verkman; Ivan Sabolic

1995-01-01

6

The first discovered water channel protein, later called aquaporin 1: molecular characteristics, functions and medical implications.  

PubMed

After a decade of work on the water permeability of red blood cells (RBC) Benga group in Cluj-Napoca, Romania, discovered in 1985 the first water channel protein in the RBC membrane. The discovery was reported in publications in 1986 and reviewed in subsequent years. The same protein was purified by chance by Agre group in Baltimore, USA, in 1988, who called in 1991 the protein CHIP28 (CHannel forming Integral membrane Protein of 28 kDa), suggesting that it may play a role in linkage of the membrane skeleton to the lipid bilayer. In 1992 the Agre group identified CHIP28's water transport property. One year later CHIP28 was named aquaporin 1, abbreviated as AQP1. In this review the molecular structure-function relationships of AQP1 are presented. In the natural or model membranes AQP1 is in the form of a homotetramer, however, each monomer has an independent water channel (pore). The three-dimensional structure of AQP1 is described, with a detailed description of the channel (pore), the molecular mechanisms of permeation through the channel of water molecules and exclusion of protons. The permeability of the pore to gases (CO(2), NH(3), NO, O(2)) and ions is also mentioned. I have also reviewed the functional roles and medical implications of AQP1 expressed in various organs and cells (microvascular endothelial cells, kidney, central nervous system, eye, lacrimal and salivary glands, respiratory apparatus, gastrointestinal tract, hepatobiliary compartments, female and male reproductive system, inner ear, skin). The role of AQP1 in cell migration and angiogenesis in relation with cancer, the genetics of AQP1 and mutations in human subjects are also mentioned. The role of AQP1 in red blood cells is discussed based on our comparative studies of water permeability in over 30 species. PMID:22705445

Benga, Gheorghe

2012-06-15

7

Drugs activating G proteins disturb cycling of ADH-dependent water channels in toad urinary bladder.  

PubMed

In the toad urinary bladder, antidiuretic hormone (ADH)-mediated changes in water permeability depend on exocytic insertion and endocytic retrieval of water channels into and from the apical membrane, respectively. Because GTP-binding proteins (G proteins) are well-recognized regulators of vesicular trafficking throughout the cell, we tested the hypothesis that drugs interfering with G protein would modify the hydrosmotic response to ADH and the ADH-regulated formation of endosomes, as assessed by luminal incorporation of a fluid-phase marker [fluorescein isothiocyanate (FITC)-dextran, 70 kDa]. Mastoparan (4 microM) and compound 48/80 (poly-p-methoxyphenylethylmethylamine; 50 micrograms/ml), added to the luminal side of the toad urinary bladder, as well as AlF3 added to the serosal side (400 microM), inhibited ADH- and 8-bromoadenosine 3',5'-cyclic monophosphate-induced transepithelial water flow by > 50% and simultaneously enhanced cellular incorporation of FITC-dextran by > 200%. The pattern of FITC-dextran uptake observed using fluorescence microscopy both in scraped cells and in the intact bladder was granular, suggesting fluid-phase endocytosis. Mastoparan and AlF3, which are both probes of G proteins, increased FITC-dextran uptake only in the presence of ADH and a transepithelial osmotic gradient, i.e., under conditions where water channel-carrying endosomes presumably cycle. Therefore, we suggest that the ADH-dependent cycling of water channels could be controlled by one or more G proteins associated with the apical membrane and/or the water channel-carrying vesicles. PMID:7544530

Boom, A; Flamion, B; Abramow, M; Beauwens, R

1995-08-01

8

Developmental Gene Expression and Tissue Distribution of the CHIP28 Water Channel Protein  

Microsoft Academic Search

The CHIP28 water channel is a major component of red cell and renal tubule membranes; however, its ontogeny and tissue distribution remain undefined. Three patterns of expression were identified when CHIP28 mRNA was surveyed by in situ hybridization histochemistry in rats between embryonic day 14 and maturity. (i) CHIP28 mRNA and protein were very abundant in hematopoietic tissue and kidneys

Carolyn Bondy; Edward Chin; Barbara L. Smith; Gregory M. Preston; Peter Agre

1993-01-01

9

Highly permeable polymeric membranes based on the incorporation of the functional water channel protein Aquaporin Z  

PubMed Central

The permeability and solute transport characteristics of amphiphilic triblock-polymer vesicles containing the bacterial water-channel protein Aquaporin Z (AqpZ) were investigated. The vesicles were made of a block copolymer with symmetric poly-(2-methyloxazoline)-poly-(dimethylsiloxane)-poly-(2-methyloxazoline) (PMOXA15-PDMS110-PMOXA15) repeat units. Light-scattering measurements on pure polymer vesicles subject to an outwardly directed salt gradient in a stopped-flow apparatus indicated that the polymer vesicles were highly impermeable. However, a large enhancement in water productivity (permeability per unit driving force) of up to ?800 times that of pure polymer was observed when AqpZ was incorporated. The activation energy (Ea) of water transport for the protein-polymer vesicles (3.4 kcal/mol) corresponded to that reported for water-channel-mediated water transport in lipid membranes. The solute reflection coefficients of glucose, glycerol, salt, and urea were also calculated, and indicated that these solutes are completely rejected. The productivity of AqpZ-incorporated polymer membranes was at least an order of magnitude larger than values for existing salt-rejecting polymeric membranes. The approach followed here may lead to more productive and sustainable water treatment membranes, whereas the variable levels of permeability obtained with different concentrations of AqpZ may provide a key property for drug delivery applications.

Kumar, Manish; Grzelakowski, Mariusz; Zilles, Julie; Clark, Mark; Meier, Wolfgang

2007-01-01

10

Immunolocalization of the Mercurial-Insensitive Water Channel and Glycerol Intrinsic Protein in Epithelial Cell Plasma Membranes  

Microsoft Academic Search

Two water channel homologs were cloned recently from rat kidney, mercurial-insensitive water channel (MIWC) and glycerol intrinsic protein (GLIP). Polyclonal antibodies were raised against synthetic C-terminal peptides and purified by affinity chromatography. MIWC and GLIP antibodies recognized proteins in rat kidney with an apparent molecular mass of 30 and 27 kDa, respectively, and did not cross-react. By immunofluorescence, MIWC and

Antonio Frigeri; Michael A. Gropper; C. W. Turck; A. S. Verkman

1995-01-01

11

Water channel protein AQP3 is present in epithelia exposed to the environment of possible water loss.  

PubMed

Aquaporins (AQPs) are membrane water channel proteins expressed in various tissues in the body. We surveyed the immunolocalization of AQP3, an isoform of the AQP family, in rat epithelial tissues. AQP3 was localized to many epithelial cells in the urinary, digestive, and respiratory tracts and in the skin. In the urinary tract, AQP3 was present at transitional epithelia. In the digestive tract, abundant AQP3 was found in the stratified epithelia in the upper part, from the oral cavity to the forestomach, and in the simple and stratified epithelia in the lower part, from the distal colon to the anal canal. In the respiratory tract, AQP3 was present in the pseudostratified ciliated epithelia from the nasal cavity to the intrapulmonary bronchi. In the skin, AQP3 was present in the epidermis. Interestingly, AQP3 was present at the basal aspects of the epithelia: in the basolateral membranes in the simple epithelia and in the multilayered epithelia at plasma membranes of the basal to intermediate cells. During development of the skin, AQP3 expression commenced late in fetal life. Because these AQP3-positive epithelia have a common feature, i.e., they are exposed to an environment of possible water loss, we propose that AQP3 could serve as a water channel to provide these epithelial cells with water from the subepithelial side to protect them against dehydration. (J Histochem Cytochem 47:1275-1286, 1999) PMID:10490456

Matsuzaki, T; Suzuki, T; Koyama, H; Tanaka, S; Takata, K

1999-10-01

12

A Simple Water Channel  

ERIC Educational Resources Information Center

Describes a simple water channel, for use with an overhead projector. It is run from a water tap and may be used for flow visualization experiments, including the effect of streamlining and elementary building aerodynamics. (MLH)

White, A. S.

1976-01-01

13

A Simple Water Channel  

ERIC Educational Resources Information Center

|Describes a simple water channel, for use with an overhead projector. It is run from a water tap and may be used for flow visualization experiments, including the effect of streamlining and elementary building aerodynamics. (MLH)|

White, A. S.

1976-01-01

14

Correlation of aquaporin-1 water channel protein expression with tumor angiogenesis in human astrocytoma.  

PubMed

Aquaporin-1 (AQP1) is a water channel protein, widely expressed in epithelial and endothelial cells, known to be associated with invasion, angiogenesis, cell migration and formation of tumour oedema in several malignancies. We investigated the pattern of immunohistochemical expression of AQP1 in human astrocytomas and its role in tumour angiogenesis and infiltration. Immunohistochemical staining of AQP1 was performed in astrocytomas of grade II, III and IV. Intensity and pattern of expression were analysed. Non-neoplastic brain tissues served as control. There was a significant increase in the intensity of AQP1 expression from low-grade to high-grade astrocytomas (p<0.0001). Despite intense expression of AQP1 in astrocytoma grade IV, we observed strong regional differences. AQP1 up-regulation was predominantly located perivascularly, in areas of tumour infiltration, distant from the necrotic tumour core. AQP1 expression correlates with the grade of malignancy and is associated with angiogenesis, as well as with invasion of grade IV tumour in areas of tumour infiltration. Suppression of AQP1 expression could be a potential means of reducing invasion of glioma cells. PMID:23393355

El Hindy, Nicolai; Bankfalvi, Agnes; Herring, Arne; Adamzik, Michael; Lambertz, Nicole; Zhu, Yuan; Siffert, Winfried; Sure, Ulrich; Sandalcioglu, I Erol

2013-02-01

15

Ferritin Protein Nanocage Ion Channels  

PubMed Central

Ferritin protein nanocages, self-assembled from four-?-helix bundle subunits, use Fe2+ and oxygen to synthesize encapsulated, ferric oxide minerals. Ferritin minerals are iron concentrates stored for cell growth. Ferritins are also antioxidants, scavenging Fenton chemistry reactants. Channels for iron entry and exit consist of helical hairpin segments surrounding the 3-fold symmetry axes of the ferritin nanocages. We now report structural differences caused by amino acid substitutions in the Fe2+ ion entry and exit channels and at the cytoplasmic pores, from high resolution (1.3–1.8 ?) protein crystal structures of the eukaryotic model ferritin, frog M. Mutations that eliminate conserved ionic or hydrophobic interactions between Arg-72 and Asp-122 and between Leu-110 and Leu-134 increase flexibility in the ion channels, cytoplasmic pores, and/or the N-terminal extensions of the helix bundles. Decreased ion binding in the channels and changes in ordered water are also observed. Protein structural changes coincide with increased Fe2+ exit from dissolved, ferric minerals inside ferritin protein cages; Fe2+ exit from ferritin cages depends on a complex, surface-limited process to reduce and dissolve the ferric mineral. High concentrations of bovine serum albumin or lysozyme (protein crowders) to mimic the cytoplasm restored Fe2+ exit in the variants to wild type. The data suggest that fluctuations in pore structure control gating. The newly identified role of the ferritin subunit N-terminal extensions in gating Fe2+ exit from the cytoplasmic pores strengthens the structural and functional analogies between ferritin ion channels in the water-soluble protein assembly and membrane protein ion channels gated by cytoplasmic N-terminal peptides.

Tosha, Takehiko; Behera, Rabindra K.; Ng, Ho-Leung; Bhattasali, Onita; Alber, Tom; Theil, Elizabeth C.

2012-01-01

16

Proton transfer in water wires in proteins: modulation by local constraint and polarity in gramicidin a channels.  

PubMed

The transfer of protons in membrane proteins is an essential phenomenon in biology. However, the basic rules by which H(+) transfer occurs in water wires inside proteins are not well characterized. In particular, the effects of specific atoms and small groups of atoms on the rate of H(+) transfer in water wires are not known. In this study, new covalently linked gramicidin-A (gA) peptides were synthesized, and the effects of specific atoms and peptide constraints on the rate of H(+) transfer were measured in single molecules. The N-termini of two gA peptides were linked to various molecules: S,S-cyclopentane diacid, R,R-cyclopentane diacid, and succinic acid. Single-channel proton conductances (g(H)) were measured at various proton concentrations ([H(+)]) and compared to previous measurements obtained in the S,S- and R,R-dioxolane-linked as well as in native gA channels. Replacing the S,S-dioxolane by an S,S-cyclopentane had no effects on the g(H)-[H(+)] relationships, suggesting that the constrained and continuous transition between the two gA peptides via these S,S linkers is ultimately responsible for the two- to fourfold increase in g(H) relative to native gA channels. It is likely that constraining a continuous transition between the two gA peptides enhances the rate of H(+) transfer in water wires by decreasing the number of water wire configurations that do not transfer H(+) at higher rates as in native gA channels (a decrease in the activation entropy of the system). On the other hand, g(H) values in the R,R-cyclopentane are considerably larger than those in R,R-dioxolane-linked gA channels. One explanation would be that the electrostatic interactions between the oxygens in the dioxolane and adjacent carbonyls in the R,R-dioxolane-linked gA channel attenuate the rate of H(+) transfer in the middle of the pore. Interestingly, g(H)-[H(+)] relationships in the R,R-cyclopentane-linked gA channel are quite similar to those in native gA channels. g(H) values in succinyl-linked gA channels display a wide distribution of values that is well represented by a bigaussian. The larger peaks of these distributions are similar to g(H) values measured in native gA channel. This observation is also consistent with the notion that constraining the transition between the two beta-helical gA peptides enhances the rate of H(+) transfer in water wires by decreasing the activation entropy of the system. PMID:17496018

Narayan, Shasikala; Wyatt, Debra L; Crumrine, David S; Cukierman, Samuel

2007-05-11

17

Effect of Atractylodes macrocephala on Hypertonic Stress-Induced Water Channel Protein Expression in Renal Collecting Duct Cells  

PubMed Central

Edema is a symptom that results from the abnormal accumulation of fluid in the body. The cause of edema is related to the level of aquaporin (AQP)2 protein expression, which regulates the reabsorption of water in the kidney. Edema is caused by overexpression of the AQP2 protein when the concentration of Na+ in the blood increases. The rhizome of Atractylodes macrocephala has been used in traditional oriental medicine as a diuretic drug; however, the mechanism responsible for the diuretic effect of the aqueous extract from A. macrocephala rhizomes (AAMs) has not yet been identified. We examined the effect of the AAM on the regulation of water channels in the mouse inner medullary collecting duct (mIMCD)-3 cells under hypertonic stress. Pretreatment of AAM attenuates a hypertonicity-induced increase in AQP2 expression as well as the trafficking of AQP2 to the apical plasma membrane. Tonicity-responsive enhancer binding protein (TonEBP) is a transcription factor known to play a central role in cellular homeostasis by regulating the expression of some proteins, including AQP2. Western immunoblot analysis demonstrated that the protein and mRNA expression levels of TonEBP also decrease after AAM treatment. These results suggest that the AAM has a diuretic effect by suppressing water reabsorption via the downregulation of the TonEBP-AQP2 signaling pathway.

Lee, Yong Pyo; Lee, Yun Jung; Lee, So Min; Yoon, Jung Joo; Kim, Hye Yoom; Kang, Dae Gill; Lee, Ho Sub

2012-01-01

18

The aquaporin family of water channels in kidney  

Microsoft Academic Search

The aquaporin family of water channels in kidney. The longstanding puzzle of membrane water permeability was advanced by the discovery of channel-forming integral protein (CHIP). This protein was shown to function as a water channel when expressed in Xenopus oocytes or when reconstituted into synthetic membranes. Site-directed mutagenesis and electron crystallography reveal tetrameric organization of CHIP, and the two halves

Søren Nielsen; Peter Agre

1995-01-01

19

Water channel activities of Mimosa pudica plasma membrane intrinsic proteins are regulated by direct interaction and phosphorylation  

Microsoft Academic Search

cDNAs encoding aquaporins PIP1;1, PIP2;1, and TIP1;1 were isolated from Mimosa pudica (Mp) cDNA library. MpPIP1;1 exhibited no water channel activity; however, it facilitated the water channel activity of MpPIP2;1 in a phosphorylation-dependent manner. Mutagenesis analysis revealed that Ser-131 of MpPIP1;1 was phosphorylated by PKA and that cooperative regulation of the water channel activity of MpPIP2;1 was regulated by phosphorylation

Yusuke Temmei; Shinichi Uchida; Daisuke Hoshino; Nobuyuki Kanzawa; Michio Kuwahara; Sei Sasaki; Takahide Tsuchiya

2005-01-01

20

Aquaporins: The renal water channels.  

PubMed

Water is the most abundant molecule in any cell. Specialized membrane channel, proteins called aquaporins, facilitate water transport across cell membranes. At least seven aquaporins (AQP): 1, 2, 3, 4, 6, 7, and 11 are expressed in the kidneys. Aquaporins play a role in both the short-term and long-term regulation of water balance as well as in the pathophysiology of water balance disorders. Aquaporin is composed of a single peptide chain consisting of approximately 270 amino acids. Inherited central and nephrogenic diabetes insipidus are primarily due to the decreased expression of AQP2 while mutation in the AQP2 molecule is responsible for inherited central diabetes insipidus. In acquired causes of nephrogenic diabetes insipidus, there is a downregulation of AQP2 expression in the inner medulla of the kidney. Nephrotic syndrome is characterized by excessive sodium and water reabsorption, although in spite of this, patients do not develop hyponatremia. There is a marked downregulation of both AQP2 and AQP3 expression, which could be a physiologic response to extracellular water reabsorption in patients with nephrotic syndrome. There are some conditions in which aquaporin expression has been found to increase such as experimentally induced heart failure, cirrhosis, and pregnancy. Some drugs such as cisplatin and cyclosporine, also alter the expression of aquaporins. The three-pore model of peritoneal transport depicts the importance of aquaporins. Thus, the understanding of renal water channels has solved the mystery behind many water balance disorders. Further insights into the molecular structure and biology of aquaporins will help to lay a foundation for the development of future drugs. PMID:20142913

Agarwal, S K; Gupta, A

2008-07-01

21

A family of transcripts encoding water channel proteins: tissue-specific expression in the common ice plant.  

PubMed Central

Seawater-strength salt stress of the ice plant (Mesembryanthemum crystallinum) initially results in wilting, but full turgor is restored within approximately 2 days. We are interested in a mechanistic explanation for this behavior and, as a requisite for in-depth biochemical studies, have begun to analyze gene expression changes in roots coincident with the onset of stress. cDNAs that suggested changes in mRNA amount under stress were found; their deduced amino acid sequences share homologies with proteins of the Mip (major intrinsic protein) gene family and potentially encode aquaporins. One transcript, MipB, was found only in root RNA, whereas two other transcripts, MipA and MipC, were detected in roots and leaves. Transcript levels of MipB were of low abundance. All transcripts declined initially during salt stress but later recovered to at least prestress level. The most drastic decline was in MipA and MipC transcripts. MipA mRNA distribution in roots detected by in situ hybridization indicated that the transcript was present in all cells in the root tip. In the expansion zone of the root where vascular bundles differentiate, MipA transcript amounts were most abundant in the endodermis. In older roots, which had undergone secondary growth, MipA was highly expressed in cell layers surrounding individual xylem strands. MipA was also localized in leaf vascular tissue and, in lower amounts, in mesophyll cells. Transcripts for MipB seemed to be present exclusively in the tip of the root, in a zone before and possibly coincident with the development of a vascular system. MipA- and MipB-encoded proteins expressed in Xenopus oocytes led to increased water permeability. mRNA fluctuations of the most highly expressed MipA and MipC coincided with turgor changes in leaves under stress. As the leaves regained turgor, transcript levels of these water channel proteins increased.

Yamada, S; Katsuhara, M; Kelly, W B; Michalowski, C B; Bohnert, H J

1995-01-01

22

Identification and characterization of functional aquaporin water channel protein from alimentary tract of whitefly, Bemisia tabaci  

Technology Transfer Automated Retrieval System (TEKTRAN)

Some hemipteran xylem and phloem feeding insects have evolved specialized alimentary structures or filter chambers that rapidly transport water for excretion or osmoregulation. In the whitefly, Bemisia tabaci, mass movement of water through opposing alimentary tract tissues within the filter chamber...

23

The role of water channel proteins and nitric oxide signaling in rice seed germination  

Microsoft Academic Search

Previous studies have demonstrated the possible role of several aquaporins in seed germination. But systematic investigation of the role of aquaporin family members in this process is lacking. Here, the developmental regulation of plasma membrane intrinsic protein (PIP) expression throughout germination and post-germination processes in rice embryos was analyzed. The expression patterns of the PIPs suggest these aquaporins play different

Hong-Yan Liu; Xin Yu; Da-Yong Cui; Mei-Hao Sun; Wei-Ning Sun; Zhang-Cheng Tang; Sang-Soo Kwak; Wei-Ai Su

2007-01-01

24

Water channel activities of Mimosa pudica plasma membrane intrinsic proteins are regulated by direct interaction and phosphorylation.  

PubMed

cDNAs encoding aquaporins PIP1;1, PIP2;1, and TIP1;1 were isolated from Mimosa pudica (Mp) cDNA library. MpPIP1;1 exhibited no water channel activity; however, it facilitated the water channel activity of MpPIP2;1 in a phosphorylation-dependent manner. Mutagenesis analysis revealed that Ser-131 of MpPIP1;1 was phosphorylated by PKA and that cooperative regulation of the water channel activity of MpPIP2;1 was regulated by phosphorylation of Ser-131 of MpPIP1;1. Immunoprecipitation analysis revealed that MpPIP1;1 binds directly to MpPIP2;1 in a phosphorylation-independent manner, suggesting that phosphorylation of Ser-131 of MpPIP1;1 is involved in regulation of the structure of the channel complex with MpMIP2;1 and thereby affects water channel activity. PMID:16061230

Temmei, Yusuke; Uchida, Shinichi; Hoshino, Daisuke; Kanzawa, Nobuyuki; Kuwahara, Michio; Sasaki, Sei; Tsuchiya, Takahide

2005-08-15

25

Partitioning of Aquaporin4 Water Channel mRNA and Protein in Gastric Glands  

Microsoft Academic Search

Immunolocalization studies in proximal, middle, and distal stomach indicated that aquaporin-4 (AQP4) protein is localized only in parietal cells located in the middle or deep regions of the gastric glands. In studies using in situ hybridization, AQP4 mRNA failed to localize in parietal cells but was identified in neighboring mucosal cells that were triangular in shape and smaller than parietal

Yan Huang; Vicky B. Tola; Pingke Fang; David I. Soybel; Alfred N. Van Hoek

2003-01-01

26

The Fusobacterium nucleatum major outer-membrane protein (FomA) forms trimeric, water-filled channels in lipid bilayer membranes.  

PubMed

The pore-forming activity of the major outer-membrane protein FomA of the anaerobic Fusobacterium nucleatum was studied in artificial lipid bilayer membranes. FomA was isolated from F. nucleatum strains Fev1, ATCC 10953, and ATCC 25586 by extraction with lithium dodecyl sulfate and lithium chloride and had an apparent molecular mass of about 40 kDa. When solubilized at low temperatures, the protein ran with an apparent molecular mass of about 62 kDa on SDS/PAGE. Cross-linking experiments and two-dimensional SDS/PAGE gave evidence that the 62-kDa protein band represented the trimeric form of FomA. The protein trimers were susceptible to SDS and temperature. The stability of the porin trimers varied among the strains. The properties of the FomA channels were studied in reconstitution experiments with black lipid bilayer membranes. The F. nucleatum porins formed channels with single-channel conductances in the range 0.66-1.30 nS in M KCl. The single-channel conductance was a function of the mobilities of the ions present in the aqueous solution bathing the bilayer membrane. This means that FomA forms general diffusion channels since (a) the conductance showed a linear dependence on the salt concentration, (b) the ion selectivity was small and varied for the three strains, and (c) the channels did not exhibit any binding site for maltotriose or triglycine. The water-filled channel was voltage dependent, and conductance decrements were observed at transmembrane potentials of +/- 50 mV. The conductance decrement steps were about one-third of the total conductance of a functional unit in its fully 'open' state. This strongly suggests that the trimer is the functional unit of the porin. PMID:7588760

Kleivdal, H; Benz, R; Jensen, H B

1995-10-01

27

Water channels in peritoneal dialysis.  

PubMed

Peritoneal dialysis involves diffusive and convective transports and osmosis through the highly vascularized peritoneal membrane. Several lines of evidence have demonstrated that the water channel aquaporin-1 (AQP1) corresponds to the ultrasmall pore predicted by the modelization of peritoneal transport. Proof-of-principle studies have shown that up-regulation of the expression of AQP1 in peritoneal capillaries is reflected by increased water permeability and ultrafiltration, without affecting the osmotic gradient and the permeability for small solutes. Inversely, studies in Aqp1 mice have shown that haploinsufficiency in AQP1 is reflected by significant attenuation of water transport. Recent studies have identified lead compounds that could act as agonists of aquaporins, as well as putative binding sites and potential mechanisms of gating the water channel. By modulating water transport, these pharmacological agents could have clinically relevant effects in targeting specific tissues or disease states. These studies on the peritoneal membrane also provide an experimental framework to investigate the role of water channels in the endothelium and various cell types. PMID:21170876

Devuyst, Olivier

28

Computational optimization of synthetic water channels.  

SciTech Connect

Membranes for liquid and gas separations and ion transport are critical to water purification, osmotic energy generation, fuel cells, batteries, supercapacitors, and catalysis. Often these membranes lack pore uniformity and robustness under operating conditions, which can lead to a decrease in performance. The lack of uniformity means that many pores are non-functional. Traditional membranes overcome these limitations by using thick membrane materials that impede transport and selectivity, which results in decreased performance and increased operating costs. For example, limitations in membrane performance demand high applied pressures to deionize water using reverse osmosis. In contrast, cellular membranes combine high flux and selective transport using membrane-bound protein channels operating at small pressure differences. Pore size and chemistry in the cellular channels is defined uniformly and with sub-nanometer precision through protein folding. The thickness of these cellular membranes is limited to that of the cellular membrane bilayer, about 4 nm thick, which enhances transport. Pores in the cellular membranes are robust under operating conditions in the body. Recent efforts to mimic cellular water channels for efficient water deionization produced a significant advance in membrane function. The novel biomimetic design achieved a 10-fold increase in membrane permeability to water flow compared to commercial membranes and still maintained high salt rejection. Despite this success, there is a lack of understanding about why this membrane performs so well. To address this lack of knowledge, we used highperformance computing to interrogate the structural and chemical environments experienced by water and electrolytes in the newly created biomimetic membranes. We also compared the solvation environments between the biomimetic membrane and cellular water channels. These results will help inform future efforts to optimize and tune the performance of synthetic biomimetic membranes for applications in water purification, energy, and catalysis.

Rogers, David Michael; Rempe, Susan L. B.

2012-12-01

29

Aquaporin water channels - from atomic structure to clinical medicine  

Microsoft Academic Search

The water permeability of biological membranes has been a longstanding problem in physiology, but the proteins responsible for this remained unknown until discovery of the aquaporin 1 (AQP1) water channel protein. AQP1 is selectively permeated by water driven by osmotic gradients. The atomic structure of human AQP1 has recently been defined. Each subunit of the tetramer contains an individual aqueous

Peter Agre; Landon S. King; Masato Yasui; Wm B. Guggino; Ole Petter Ottersen; Yoshinori Fujiyoshi; Andreas Engel; Søren Nielsen

2002-01-01

30

Regulation of Ion Channels by G Proteins  

NSDL National Science Digital Library

This Teaching Resource provides lecture notes and slides for a class covering regulation of ion channels by G proteins and is part of the course "Cell Signaling Systems: A Course for Graduate Students." The lecture begins with an overview of calcium channels and then proceeds to describe the interaction of signaling molecules with calcium channels.

Maria Diverse-Pierluissi (Mount Sinai School of Medicine.;Department of Pharmacology and Biological Chemistry REV)

2005-08-16

31

Aquaporin water channels in gastrointestinal physiology.  

PubMed

Fluid transport is a major function of the gastrointestinal (GI) tract with more than 9 litres of fluid being absorbed or secreted across epithelia in human salivary gland, stomach, the hepatobiliary tract, pancreas, small intestine and colon. This review evaluates the evidence that aquaporin-type water channels are involved in GI fluid transport. The aquaporins are a family of small ( approximately 30 kDa) integral membrane proteins that function as water channels. At least seven aquaporins are expressed in various tissues in the GI tract: AQP1 in intrahepatic cholangiocytes, AQP4 in gastric parietal cells, AQP3 and AQP4 in colonic surface epithelium, AQP5 in salivary gland, AQP7 in small intestine, AQP8 in liver, pancreas and colon, and AQP9 in liver. There are functional data suggesting that some GI cell types expressing aquaporins have high or regulated water permeability; however, there has been no direct evidence for a role of aquaporins in GI physiology. Recently, transgenic mice have been generated with selective deletions of various aquaporins. Preliminary evaluation of GI function suggests a role for AQP1 in dietary fat processing and AQP4 in colonic fluid absorption. Further study of aquaporin function in the GI tract should provide new insights into normal GI physiology and disease mechanisms, and may yield novel therapies to regulate fluid movement in GI diseases. PMID:10332084

Ma, T; Verkman, A S

1999-06-01

32

The plasma membrane of Arabidopsis thaliana contains a mercury- insensitive aquaporin that is a homolog of the tonoplast water channel protein TIP  

Microsoft Academic Search

Plant cells contain proteins that are members of the major intrinsic protein (MIP) family, an ancient family of membrane channel proteins characterized by six membrane-spanning domains and two asparagine-proline-alanine (NPA) amino acid motifs in the two halves of the protein. We recently demonstrated that y- TIP, one of the MIP homologs found in the vacuolar membrane of plant cells, is

Mark J. Daniels; T. Erik Mirkov; Maarten J. Chrispeels

1994-01-01

33

Aquaporin water channels: molecular mechanisms for human diseases1  

Microsoft Academic Search

Although water is the major component of all biolog- ical £uids, the molecular pathways for water transport across cell membranes eluded identi¢cation until the discovery of the aquaporin family of water channels. The atomic structure of mammalian AQP1 illustrates how this family of proteins is freely permeated by water but not protons (hydronium ions, H3O + ). De¢nition of the

Peter Agre; David Kozono

2003-01-01

34

Theoretical and computational studies of microscopic water channels  

NASA Astrophysics Data System (ADS)

Water channels are ubiquitous in all life forms. A notable example is aquaporins (AQPs), a family of proteins which mainly function as passive water channels in cell membranes. The availability of the crystal structures of several AQPs in recent years allowed us to study them in atomic details. We performed molecular dynamics (MD) simulations on AQPs in lipid bilayers to study water permeation through these channels. We also simulated water conduction in carbon nanotubes, serving as simplified models for biological channels. We developed theories and methodologies aimed to reproduce and predict important experimental quantities of water channels from simulations. We showed that the diffusion permeability (pd), which is measured by tracer diffusion in experiments, can be calculated from equilibrium MD simulations. In order to calculate the osmotic permeability (p f), which is experimentally measured in the presence of a solute concentration difference, we developed a method to induce a hydrostatic pressure difference across the membrane under periodic boundary conditions. We calculated the osmotic permeability for aquaporin-1 using this method, which agrees with experiments. Using a continuous-time random-walk model, we showed that for single-file water channels, the ratio of p f to pd is roughly equal to the number of water molecules in the channel. Proton transfer through single water file was studied theoretically using network thermodynamics. Finally, we proposed a new model for general water channels, which gives a quantitative relationship between water permeations under equilibrium and non-equilibrium conditions, and therefore allows one to calculate pf from equilibrium MD simulations.

Zhu, Fangqiang

35

Ion Channel Regulation by Protein Palmitoylation*  

PubMed Central

Protein S-palmitoylation, the reversible thioester linkage of a 16-carbon palmitate lipid to an intracellular cysteine residue, is rapidly emerging as a fundamental, dynamic, and widespread post-translational mechanism to control the properties and function of ligand- and voltage-gated ion channels. Palmitoylation controls multiple stages in the ion channel life cycle, from maturation to trafficking and regulation. An emerging concept is that palmitoylation is an important determinant of channel regulation by other signaling pathways. The elucidation of enzymes controlling palmitoylation and developments in proteomics tools now promise to revolutionize our understanding of this fundamental post-translational mechanism in regulating ion channel physiology.

Shipston, Michael J.

2011-01-01

36

Involvement of Mitogen-Activated Protein Kinase Pathways in Expression of the Water Channel Protein Aquaporin-4 after Ischemia in Rat Cortical Astrocytes  

PubMed Central

Abstract Brain edema after ischemic brain injury is a key determinant of morbidity and mortality. Aquaporin-4 (AQP4) plays an important role in water transport in the central nervous system and is highly expressed in brain astrocytes. However, the AQP4 regulatory mechanisms are poorly understood. In this study, we investigated whether mitogen-activated protein kinases (MAPKs), which are involved in changes in osmolality, might mediate AQP4 expression in models of rat cortical astrocytes after ischemia. Increased levels of AQP4 in primary cultured astrocytes subjected to oxygen-glucose deprivation (OGD) and 2?h of reoxygenation were observed, after which they immediately decreased at 0?h of reoxygenation. Astrocytes exposed to OGD injury had significantly increased phosphorylation of three kinds of MAPKs. Treatment with SB203580, a selective p38 MAPK inhibitor, or SP600125, a selective c-Jun N-terminal kinase inhibitor, significantly attenuated the return of AQP4 to its normal level, and SB203580, but not SP600125, significantly decreased cell death. In an in vivo study, AQP4 expression was upregulated 1–3 days after reperfusion, which was consistent with the time course of p38 phosphorylation and activation, and decreased by the p38 inhibition after transient middle cerebral artery occlusion (MCAO). These results suggest that p38 MAPK may regulate AQP4 expression in cortical astrocytes after ischemic injury.

Kamada, Hiroshi; Endo, Hidenori; Narasimhan, Purnima; Lee, Yong-Sun; Chan, Pak H.

2012-01-01

37

Increased aquaporin 1 water channel expression inhuman brain tumours  

Microsoft Academic Search

Aquaporin 1 is a water channel protein. There was little aquaporin 1 immunoreactivity in normal brain parenchyma. In astrocytomas, aquaporin 1 was expressed in microvessel endothelia and neoplastic astrocytes. In metastatic carcinomas, aquaporin 1 was present in microvessel endothelia and reactive astrocytes. Aquaporin 1 may participate in the formation of brain tumour oedema.

S Saadoun; M C Papadopoulos; D C Davies; B A Bell; S Krishna

2002-01-01

38

Membrane-Protein Interactions in Mechanosensitive Channels  

PubMed Central

In this article, we examine the mechanical role of the lipid bilayer in ion channel conformation and function with specific reference to the case of the mechanosensitive channel of large conductance (MscL). In a recent article we argued that mechanotransduction very naturally arises from lipid-protein interactions by invoking a simple analytic model of the MscL channel and the surrounding lipid bilayer. In this article, we focus on improving and expanding this analytic framework for studying lipid-protein interactions with special attention to MscL. Our goal is to generate simple scaling relations which can be used to provide qualitative understanding of the role of membrane mechanics in protein function and to quantitatively interpret experimental results. For the MscL channel, we find that the free energies induced by lipid-protein interaction are of the same order as the measured free energy differences between conductance states. We therefore conclude that the mechanics of the bilayer plays an essential role in determining the conformation and function of the channel. Finally, we compare the predictions of our model to experimental results from the recent investigations of the MscL channel by a variety of investigators and suggest a suite of new experiments.

Wiggins, Paul; Phillips, Rob

2005-01-01

39

MAL decreases the internalization of the aquaporin-2 water channel  

PubMed Central

Body water homeostasis depends critically on the hormonally regulated trafficking of aquaporin-2 (AQP2) water channels in renal collecting duct epithelial cells. Several types of posttranslational modifications are clearly involved in controlling the distribution of AQP2 between intracellular vesicles and the apical plasma membrane. Little is known, however, about the protein interactions that govern the trafficking of AQP2 between these organelles. MAL is a detergent-resistant membrane-associated protein implicated in apical sorting events. We wondered, therefore, whether MAL plays a role in the regulated trafficking of AQP2 between intracellular vesicles and the apical surface. We find that AQP2 and MAL are coexpressed in epithelial cells of the kidney collecting duct. These two proteins interact, both in the native kidney and when expressed by transfection in cultured cells. The S256-phosphorylated form of AQP2 appears to interact more extensively with MAL than does the water channel protein not phosphorylated at this serine. We find that MAL is not involved in detergent-resistant membrane association or apical delivery of AQP2 in LLC-PK1 renal epithelial cells. Instead, MAL increases the S256 phosphorylation and apical surface expression of AQP2. Furthermore, internalization experiments show that MAL induces surface expression of AQP2 by attenuating its internalization. Thus, the involvement of MAL in the cell surface retention of apical membrane proteins could play an important role in regulated absorption and secretion in transporting epithelia.

Kamsteeg, Erik-Jan; Duffield, Amy S.; Konings, Irene B. M.; Spencer, Joanna; Pagel, Philipp; Deen, Peter M. T.; Caplan, Michael J.

2007-01-01

40

Communication channels between membrane bound proteins  

NASA Astrophysics Data System (ADS)

Much of what might be called biological computation takes place on the plasma membrane, a 2D liquid composed of a diverse soup of lipids and embedded proteins. Motivated by the recent discovery that these membranes seem to be tuned close to a 2D liquid-liquid critical point, we set out to understand the different channels through which membrane bound proteins can communicate. Diffusing proteins can carry out reactions like phosphorylation when they come in contact with each other. Near criticality, proteins can also exert long-ranged critical Casimir forces on one another by coupling to the local composition order parameter. By modulating the growth and breakdown of the rigid cytoskeleton, they can direct forces on even more distant regions. In addition, proteins can control the release and production of second messengers that diffuse either through the bulk, or in the plane of the membrane itself. By making simple models for these processes we bound functional measures for them as communication channels. These include information theoretic measures of bandwidth, as well as physical measures of energetic efficiency and speed. Our results will likely shed light on the functional role of clustering and other collective behaviors often seen in experiments.

Sethna, James; Machta, Benjamin; Veatch, Sarah

2012-02-01

41

Solubilization of membrane proteins in ethanol: new perspective method for isolation of ion channels  

NASA Astrophysics Data System (ADS)

In spite of the successful use of detergents for the solubilization of a number of membrane proteins, this approach has some restrictions. It is mainly due to difficulties in removing detergents from the proteins which can influence the structure and function of the isolated proteins and interfere with channel activity measurements under the reconstruction of the proteins into lipid bilayers. We have developed a method using ethanol for the extraction of membrane proteins. The dielectric constant of ethanol is between those of water and carbohydrates which aids it to penetrate into the membrane between protein and lipids. This decrease the binding of lipids to proteins and promotes protein solubilization. We have applied this approach to the isolation and reconstitution in lipid bilayer of the large subunit of the (Na+, K+)- ATPase from microsomes and from mitochondria: two Ca2+-channels, thermogenin and the KATP channel. The properties of these channels remained native.

Mironova, Galina D.

1997-06-01

42

Dual role of protein kinase C on BK channel regulation  

PubMed Central

Large conductance voltage- and Ca2+-activated potassium channels (BK channels) are important feedback regulators in excitable cells and are potently regulated by protein kinases. The present study reveals a dual role of protein kinase C (PKC) on BK channel regulation. Phosphorylation of S695 by PKC, located between the two regulators of K+ conductance (RCK1/2) domains, inhibits BK channel open-state probability. This PKC-dependent inhibition depends on a preceding phosphorylation of S1151 in the C terminus of the channel ?-subunit. Phosphorylation of only one ?-subunit at S1151 and S695 within the tetrameric pore is sufficient to inhibit BK channel activity. We further detected that protein phosphatase 1 is associated with the channel, constantly counteracting phosphorylation of S695. PKC phosphorylation at S1151 also influences stimulation of BK channel activity by protein kinase G (PKG) and protein kinase A (PKA). Though the S1151A mutant channel is activated by PKA only, the phosphorylation of S1151 by PKC renders the channel responsive to activation by PKG but prevents activation by PKA. Phosphorylation of S695 by PKC or introducing a phosphomimetic aspartate at this position (S695D) renders BK channels insensitive to the stimulatory effect of PKG or PKA. Therefore, our findings suggest a very dynamic regulation of the channel by the local PKC activity. It is shown that this complex regulation is not only effective in recombinant channels but also in native BK channels from tracheal smooth muscle.

Zhou, Xiao-Bo; Wulfsen, Iris; Utku, Emine; Sausbier, Ulrike; Sausbier, Matthias; Wieland, Thomas; Ruth, Peter; Korth, Michael

2010-01-01

43

Ground Water / Surface Water Exchange: Streambed Versus a Channel Bar  

NASA Astrophysics Data System (ADS)

The streambed is important in controlling exchange of water, solutes, and heat between streams and ground water. Processes such as sedimentation, erosion, and fluctuations in diurnal temperatures can have significant effects on the streambed hydraulic conductivity, which in turn affects fluid velocities across the streambed. The objectives of this study are to quantify the difference in flux magnitude and direction within and around a channel bar. The focus of this presentation is to compare fluxes in channel bar sediments with fluxes in the streambed to determine the effect of the upper boundary conditions on sediment fluxes. A network of piezometers was installed on and around a channel bar located within the Truckee River, a dense 6th order river network, located primarily in northwest Nevada. Instruments used were temperature loggers, pressure transducers, and stage recorders. Several methods were simultaneously utilized to quantify water and heat fluxes and to interpret the hydrodynamic processes through the streambed sediments. Numerical simulations are being completed to quantify the spatial and temporal fluid flux and heat transport in relation to varied hydraulic parameters such as variable river stage, geometry, and hydraulic conductivity. In general, we have found that surface water exchange to the streambed occurs at the upstream portion of bed features and streambed discharge dominates at the downstream bed feature. This exchange is evidenced at the channel bar as well as localized riffles and point bars adjacent to the channel bar. We found that at least two separate hydraulic conditions are evident during our study. The range in water levels between the piezometers was altered from approximately 1.25 m to a minimum of 0.10 m and the mean potentiometric surface increased by 1 m. These variations are geomorphic responses due to a flood event, inundating the channel bar, and a channel restoration project both upstream and downstream of the study area. These alterations have caused a reversal in the vertical head gradient (VHG) in some locations by up to 0.14. There also appears to be a critical stage height that alters the flux direction or magnitude. In conclusion, stage boundary conditions coupled with streambed features significantly contribute to the exchange direction. Sedimentation and erosion from restoration activities and streambed evolution also impacted fluid flux patterns due to their impact on streambed surface hydraulic conductivity patterns.

Shope, C. L.; Constantz, J. E.; Cooper, C. A.; McKay, W. A.

2007-12-01

44

Cultured human trabecular meshwork cells express aquaporin-1 water channels.  

PubMed

The identification and characterization of aquaporin-1 water channels and other related proteins has provided a molecular explanation for the enhanced permeability of a variety of epithelial tissues. Previously, we documented the distribution of aquaporin-1 in the human eye, which included the trabecular meshwork; the primary outflow channel for aqueous humor. The goal of this study was to determine if aquaporin-1 could be detected in cultures of human trabecular meshwork cells. Using primers specific for aquaporin-1, reverse transcription combined with polymerase chain reaction yielded a product of the appropriate size with total RNA prepared from the human trabecular meshwork cells. The presence of this product and its size (298 base pairs), is consistent with the presence of an aquaporin-1 message in these cells. Indirect immunofluorescence microscopy with affinity purified antibodies against a fusion protein containing the carboxy tail of aquaporin-1 showed specific labeling of the plasma membrane and immunoblotting identified a band of Mr 28,000 which agrees with the molecular size of aquaporin-1. The presence of aquaporin-1 in human trabecular meshwork cells, the predominant cell-type of the primary outflow region of the human eye, suggests that water channels may be involved with the movement of aqueous fluid out of the eye. In addition, the existence of aquaporin-1 on cultures of human trabecular meshwork cells provides an in vitro model to study the endogenous expression of aquaporin-1 and its possible role in the regulation of aqueous outflow. PMID:8974838

Stamer, W D; Seftor, R E; Snyder, R W; Regan, J W

1995-12-01

45

Determinants of Water Permeability through Nanoscopic Hydrophilic Channels  

PubMed Central

Naturally occurring pores show a variety of polarities and sizes that are presumably directly linked to their biological function. Many biological channels are selective toward permeants similar or smaller in size than water molecules, and therefore their pores operate in the regime of single-file water pores. Intrinsic factors affecting water permeability through such pores include the channel-membrane match, the structural stability of the channel, the channel geometry and channel-water affinity. We present an extensive molecular dynamics study on the role of the channel geometry and polarity on the water osmotic and diffusive permeability coefficients. We show that the polarity of the naturally occurring peptidic channels is close to optimal for water permeation, and that the water mobility for a wide range of channel polarities is essentially length independent. By systematically varying the geometry and polarity of model hydrophilic pores, based on the fold of gramicidin A, the water density, occupancy, and permeability are studied. Our focus is on the characterization of the transition between different permeation regimes in terms of the structure of water in the pores, the average pore occupancy and the dynamics of the permeating water molecules. We show that a general relationship between osmotic and diffusive water permeability coefficients in the single-file regime accounts for the time averaged pore occupancy, and that the dynamics of the permeating water molecules through narrow non single file channels effectively behaves like independent single-file columns.

Portella, Guillem; de Groot, Bert L.

2009-01-01

46

Water Channel (Aquaporin 1) Expression and Distribution in Mammary Carcinomas and Glioblastomas  

Microsoft Academic Search

The aquaporins represent a family of transmembrane water channel proteins that are widely distributed in various tissues throughout the body and play a major role in transcellular and transepithelial water movement. Most tumors have been shown to exhibit high vascular permeability and high interstitial fluid pressure, but the transport pathways for water within tumors remain unknown. In this study, we

Mitsuhiro Endo; Rakesh K. Jain; Brian Witwer; Dennis Brown

1999-01-01

47

Structural basis of water-specific transport through the AQP1 water channel  

Microsoft Academic Search

Water channels facilitate the rapid transport of water across cell membranes in response to osmotic gradients. These channels are believed to be involved in many physiological processes that include renal water conservation, neuro-homeostasis, digestion, regulation of body temperature and reproduction. Members of the water channel superfamily have been found in a range of cell types from bacteria to human. In

Haixin Sui; Bong-Gyoon Han; John K. Lee; Peter Walian; Bing K. Jap

2001-01-01

48

Nephrogenic diabetes insipidus in mice lacking aquaporin-3 water channels.  

PubMed

Aquaporin-3 (AQP3) is a water channel expressed at the basolateral plasma membrane of kidney collecting-duct epithelial cells. The mouse AQP3 cDNA was isolated and encodes a 292-amino acid water/glycerol-transporting glycoprotein expressed in kidney, large airways, eye, urinary bladder, skin, and gastrointestinal tract. The mouse AQP3 gene was analyzed, and AQP3 null mice were generated by targeted gene disruption. The growth and phenotype of AQP3 null mice were grossly normal except for polyuria. AQP3 deletion had little effect on AQP1 or AQP4 protein expression but decreased AQP2 protein expression particularly in renal cortex. Fluid consumption in AQP3 null mice was more than 10-fold greater than that in wild-type litter mates, and urine osmolality (<275 milliosmol) was much lower than in wild-type mice (>1,200 milliosmol). After 1-desamino-8-d-arginine-vasopressin administration or water deprivation, the AQP3 null mice were able to concentrate their urine partially to approximately 30% of that in wild-type mice. Osmotic water permeability of cortical collecting-duct basolateral membrane, measured by a spatial filtering optics method, was >3-fold reduced by AQP3 deletion. To test the hypothesis that the residual concentrating ability of AQP3 null mice was due to the inner medullary collecting-duct water channel AQP4, AQP3/AQP4 double-knockout mice were generated. The double-knockout mice had greater impairment of urinary-concentrating ability than did the AQP3 single-knockout mice. Our findings establish a form of nephrogenic diabetes insipidus produced by impaired water permeability in collecting-duct basolateral membrane. Basolateral membrane aquaporins may thus provide blood-accessible targets for drug discovery of aquaretic inhibitors. PMID:10737773

Ma, T; Song, Y; Yang, B; Gillespie, A; Carlson, E J; Epstein, C J; Verkman, A S

2000-04-11

49

Fluctuation driven active molecular transport in passive channel proteins  

NASA Astrophysics Data System (ADS)

Living cells interact with their extracellular environment through the cell membrane, which acts as a protective permeability barrier for preserving the internal integrity of the cell. However, cell metabolism requires controlled molecular transport across the cell membrane, a function that is fulfilled by a wide variety of transmembrane proteins, acting as either passive or active transporters. In this talk it is argued that, contrary to the general belief, in active cell membranes passive and spatially asymmetric channel proteins can act as active transporters by consuming energy from nonequilibrium fluctuations fueled by cell metabolism. This assertion is demonstrated in the case of the E. coli aquaglyceroporin GlpF channel protein, whose high resolution crystal structure is manifestly asymmetric. By calculating the glycerol flux through GlpF within the framework of a stochastic model, it is found that, as a result of channel asymmetry, glycerol uptake driven by a concentration gradient is enhanced significantly in the presence of non-equilibrium fluctuations. Furthermore, the enhancement caused by a ratchet-like mechanism is larger for the outward, i.e., from the cytoplasm to the periplasm, flux than for the inward one, suggesting that the same non-equilibrium fluctuations also play an important role in protecting the interior of the cell against poisoning by excess uptake of glycerol. Preliminary data on water and sugar transport through aquaporin and maltoporin channels, respectively, are indicative of the universality of the proposed nonequilibrium-fluctuation-driven active transport mechanism. This work was supported by grants from the Univ. of Missouri Research Board, the Institute for Theoretical Sciences and the Department of Energy (DOE Contract W-7405-ENG-36), and the National Science Foundation (FIBR-0526854).

Kosztin, Ioan

2006-03-01

50

Allosteric mechanism of water-channel gating by Ca(2+)-calmodulin.  

PubMed

Calmodulin (CaM) is a universal regulatory protein that communicates the presence of calcium to its molecular targets and correspondingly modulates their function. This key signaling protein is important for controlling the activity of hundreds of membrane channels and transporters. However, understanding of the structural mechanisms driving CaM regulation of full-length membrane proteins has remained elusive. In this study, we determined the pseudoatomic structure of full-length mammalian aquaporin-0 (AQP0, Bos taurus) in complex with CaM, using EM to elucidate how this signaling protein modulates water-channel function. Molecular dynamics and functional mutation studies reveal how CaM binding inhibits AQP0 water permeability by allosterically closing the cytoplasmic gate of AQP0. Our mechanistic model provides new insight, only possible in the context of the fully assembled channel, into how CaM regulates multimeric channels by facilitating cooperativity between adjacent subunits. PMID:23893133

Reichow, Steve L; Clemens, Daniel M; Freites, J Alfredo; Németh-Cahalan, Karin L; Heyden, Matthias; Tobias, Douglas J; Hall, James E; Gonen, Tamir

2013-07-28

51

Invertebrate TRP proteins as functional models for mammalian channels  

Microsoft Academic Search

Transient receptor potential (TRP) channels constitute a large and diverse family of channel proteins that are expressed in many tissues and cell types in both vertebrates and invertebrates. While the biophysical features of many of the mammalian TRP channels have been described, relatively little is known about their biological roles. Invertebrate TRPs offer valuable genetic handles for characterizing the functions

Joris Vriens; Grzegorz Owsianik; Thomas Voets; Guy Droogmans; Bernd Nilius

2004-01-01

52

Identification of resonance waves in open water channels  

Microsoft Academic Search

This article describes a way to determine the properties of resonance (reflecting) waves in open water channels. For channels that are sensitive to resonances, information about the first resonance mode is required for controller and filter design. This research applies standard system identification techniques and is tested on an actual channel at the Central Arizona Irrigation and Drainage District, Eloy,

P. J. van Overloop; I. J. Miltenburg; X. Bombois; A. J. Clemmens; R. J. Strand; N. C. van de Giesen; R. Hut

2010-01-01

53

No Mystery! Water Carved the Outflow Channels on Mars  

Microsoft Academic Search

The enormous outflow channels of Chryse Planitia provide the best evidence that large amounts of water were once released onto the martian surface. The role of water has recently been challenged by the White Mars hypothesis, which claims that the channels were cut by CO2 gas-supported debris flows that also resurfaced the northern plains. Hoffman [Icarus, 2000] refers to a

N. Coleman

2002-01-01

54

IDENTIFICATION OF RESONANCE WAVES IN OPEN WATER CHANNELS  

Technology Transfer Automated Retrieval System (TEKTRAN)

This article presents a procedure to determine the characteristics of open water channels required for controller and filter design, with special focus on the resonance waves. Also, a new simplified model structure for open water channels is proposed. The procedure applies System Identification tool...

55

The gramicidin ion channel: a model membrane protein.  

PubMed

The linear peptide gramicidin forms prototypical ion channels specific for monovalent cations and has been extensively used to study the organization, dynamics and function of membrane-spanning channels. In recent times, the availability of crystal structures of complex ion channels has challenged the role of gramicidin as a model membrane protein and ion channel. This review focuses on the suitability of gramicidin as a model membrane protein in general, and the information gained from gramicidin to understand lipid-protein interactions in particular. Special emphasis is given to the role and orientation of tryptophan residues in channel structure and function and recent spectroscopic approaches that have highlighted the organization and dynamics of the channel in membrane and membrane-mimetic media. PMID:17572379

Kelkar, Devaki A; Chattopadhyay, Amitabha

2007-05-18

56

Gating of the Mechanosensitive Channel Protein MscL: The Interplay of Membrane and Protein  

PubMed Central

The mechanosensitive channel of large conductance (MscL) belongs to a family of transmembrane channel proteins in bacteria and functions as a safety valve that relieves the turgor pressure produced by osmotic downshock. MscL gating can be triggered solely by stretching of the membrane. This work reports an effort to understand this mechanotransduction by means of molecular dynamics (MD) simulation on the MscL of mycobacterium tuberculosis embedded in a palmitoyloleoylphosphatidylethanolamine membrane. Equilibrium MD under zero membrane tension produced a more compact protein structure, as measured by its radii of gyration, compared to the crystal structure, in agreement with previous experimental findings. Even under a large applied tension up to 1000 dyn/cm, the MscL lateral dimension largely remained unchanged after up to 20 ns of simulation. A nonequilibrium MD simulation of 3% membrane expansion showed a significant increase in membrane rigidity upon MscL inclusion, which can contribute to efficient mechanotransduction. Direct observation of channel opening was possible only when an explicit lateral bias force was applied to each of the five subunits of MscL in the radially outward direction. Using this force, open structures with a large pore of radius 10 Å could be obtained. The channel opening takes place in a stepwise manner and concurrently with the water chain formation across the channel, which occurs without direct involvement of protein hydrophilic residues. The N-terminal S1 helices stabilize the open structure, and the membrane asymmetry (different lipid density on the two leaflets of membrane) promotes channel opening.

Jeon, Jonggu; Voth, Gregory A.

2008-01-01

57

GIRK channel modulation by assembly with allosterically regulated RGS proteins.  

PubMed

G-protein-activated inward-rectifying K(+) (GIRK) channels hyperpolarize neurons to inhibit synaptic transmission throughout the nervous system. By accelerating G-protein deactivation kinetics, the regulator of G-protein signaling (RGS) protein family modulates the timing of GIRK activity. Despite many investigations, whether RGS proteins modulate GIRK activity in neurons by mechanisms involving kinetic coupling, collision coupling, or macromolecular complex formation has remained unknown. Here we show that GIRK modulation occurs by channel assembly with R7-RGS/G?5 complexes under allosteric control of R7 RGS-binding protein (R7BP). Elimination of R7BP occludes the G?5 subunit that interacts with GIRK channels. R7BP-bound R7-RGS/G?5 complexes and G?? dimers interact noncompetitively with the intracellular domain of GIRK channels to facilitate rapid activation and deactivation of GIRK currents. By disrupting this allosterically regulated assembly mechanism, R7BP ablation augments GIRK activity. This enhanced GIRK activity increases the drug effects of agonists acting at G-protein-coupled receptors that signal via GIRK channels, as indicated by greater antinociceptive effects of GABA(B) or ?-opioid receptor agonists. These findings show that GIRK current modulation in vivo requires channel assembly with allosterically regulated RGS protein complexes, which provide a target for modulating GIRK activity in neurological disorders in which these channels have crucial roles, including pain, epilepsy, Parkinson's disease and Down syndrome. PMID:23169654

Zhou, Hao; Chisari, Mariangela; Raehal, Kirsten M; Kaltenbronn, Kevin M; Bohn, Laura M; Mennerick, Steven J; Blumer, Kendall J

2012-11-19

58

GIRK channel modulation by assembly with allosterically regulated RGS proteins  

PubMed Central

G-protein–activated inward-rectifying K+ (GIRK) channels hyperpolarize neurons to inhibit synaptic transmission throughout the nervous system. By accelerating G-protein deactivation kinetics, the regulator of G-protein signaling (RGS) protein family modulates the timing of GIRK activity. Despite many investigations, whether RGS proteins modulate GIRK activity in neurons by mechanisms involving kinetic coupling, collision coupling, or macromolecular complex formation has remained unknown. Here we show that GIRK modulation occurs by channel assembly with R7-RGS/G?5 complexes under allosteric control of R7 RGS-binding protein (R7BP). Elimination of R7BP occludes the G?5 subunit that interacts with GIRK channels. R7BP-bound R7-RGS/G?5 complexes and G?? dimers interact noncompetitively with the intracellular domain of GIRK channels to facilitate rapid activation and deactivation of GIRK currents. By disrupting this allosterically regulated assembly mechanism, R7BP ablation augments GIRK activity. This enhanced GIRK activity increases the drug effects of agonists acting at G-protein–coupled receptors that signal via GIRK channels, as indicated by greater antinociceptive effects of GABA(B) or ?-opioid receptor agonists. These findings show that GIRK current modulation in vivo requires channel assembly with allosterically regulated RGS protein complexes, which provide a target for modulating GIRK activity in neurological disorders in which these channels have crucial roles, including pain, epilepsy, Parkinson’s disease and Down syndrome.

Zhou, Hao; Chisari, Mariangela; Raehal, Kirsten M.; Kaltenbronn, Kevin M.; Bohn, Laura M.; Mennerick, Steven J.; Blumer, Kendall J.

2012-01-01

59

Competitive magnetic immunoassay for protein detection in thin channels  

Microsoft Academic Search

Functional magnetic nanoparticles are prepared and characterized for protein detection in a magnetic separation channel. This detection method is based on a competitive immunoassay of magnetic separation in thin channels using functional magnetic nanoparticles. We used protein A–IgG complex to demonstrate the feasibility. Free IgG and fixed number of IgG-labeled microparticles were used to compete for limited sites of protein

H. Y. Tsai; S. J. Jian; S. T. Huang; C. Bor Fuh

2009-01-01

60

Corynebacterium diphtheriae: Identification and Characterization of a Channel-Forming Protein in the Cell Wall?  

PubMed Central

The cell wall fraction of the gram-positive, nontoxic Corynebacterium diphtheriae strain C8r(?) Tox? (= ATCC 11913) contained a channel-forming protein, as judged from reconstitution experiments with artificial lipid bilayer experiments. The channel-forming protein was present in detergent-treated cell walls and in extracts of whole cells obtained using organic solvents. The protein had an apparent molecular mass of about 66 kDa as determined on Tricine-containing sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels and consisted of subunits having a molecular mass of about 5 kDa. Single-channel experiments with the purified protein suggested that the protein formed channels with a single-channel conductance of 2.25 nS in 1 M KCl. Further single-channel analysis suggested that the cell wall channel is wide and water filled because it has only slight selectivity for cations over anions and its conductance followed the mobility sequence of cations and anions in the aqueous phase. Antibodies raised against PorA, the subunit of the cell wall channel of Corynebacterium glutamicum, detected both monomers and oligomers of the isolated protein, suggesting that there are highly conserved epitopes in the cell wall channels of C. diphtheriae and PorA. Localization of the protein on the cell surface was confirmed by an enzyme-linked immunosorbent assay. The prospective homology of PorA with the cell wall channel of C. diphtheriae was used to identify the cell wall channel gene, cdporA, in the known genome of C. diphtheriae. The gene and its flanking regions were cloned and sequenced. CdporA is a protein that is 43 amino acids long and does not have a leader sequence. cdporA was expressed in a C. glutamicum strain that lacked the major outer membrane channels PorA and PorH. Organic solvent extracts of the transformed cells formed in lipid bilayer membranes the same channels as the purified CdporA protein of C. diphtheriae formed, suggesting that the expressed protein is able to complement the PorA and PorH deficiency of the C. glutamicum strain. The study is the first report of a cell wall channel in a pathogenic Corynebacterium strain.

Schiffler, Bettina; Barth, Enrico; Daffe, Mamadou; Benz, Roland

2007-01-01

61

Does water drive protein folding?  

NASA Astrophysics Data System (ADS)

We investigate the thermodynamic stability of a protein in water using an all-atom molecular model. The free energy change upon protein folding is calculated using an approach that combines molecular dynamics simulations and the integral-equation theory of molecular liquids. With this computational approach, we can analyze components of free energy such as protein intramolecular energy, hydration energy, and hydration entropy. Based upon its free energy change during protein folding, we argue that water can thermodynamically contribute to the structural stability of a protein.

Maruyama, Yutaka; Harano, Yuichi

2013-08-01

62

Protein–water displacement distributions  

Microsoft Academic Search

The statistical properties of fast protein–water motions are analyzed by dynamic neutron scattering experiments. Using isotopic exchange, one probes either protein or water hydrogen displacements. A moment analysis of the scattering function in the time domain yields model-independent information such as time-resolved mean square displacements and the Gauss-deviation. From the moments, one can reconstruct the displacement distribution. Hydration water displays

Wolfgang Doster; Marcus Settles

2005-01-01

63

Regulation of voltage-dependent calcium channels by RGK proteins.  

PubMed

RGK proteins belong to the Ras superfamily of monomeric G-proteins, and currently include four members - Rad, Rem, Rem2, and Gem/Kir. RGK proteins are broadly expressed, and are the most potent known intracellular inhibitors of high-voltage-activated Ca²? (Ca(V)1 and Ca(V)2) channels. Here, we review and discuss the evidence in the literature regarding the functional mechanisms, structural determinants, physiological role, and potential practical applications of RGK-mediated inhibition of Ca(V)1/Ca(V)2 channels. This article is part of a Special Issue entitled: Calcium channels. PMID:23063948

Yang, Tingting; Colecraft, Henry M

2012-10-10

64

The Human AQP4 Gene: Definition of the Locus Encoding Two Water Channel Polypeptides in Brain  

Microsoft Academic Search

The aquaporin family of membrane water transport proteins are expressed in diverse tissues, and in brain the predominant water channel protein is AQP4. Here we report the isolation and characterization of the human AQP4 cDNAs and genomic DNA. Two cDNAs were isolated corresponding to the two initiating methionines (M1 in a 323-aa polypeptide and M23 in a 301-aa polypeptide) previously

Mingqi Lu; M. Douglas Lee; Barbara L. Smith; Jin Sup Jung; Peter Agre; Marian A. J. Verdijk; Gerard Merkx; Johan P. L. Rijss; Peter M. T. Deen

1996-01-01

65

Mechanosensitivity of ion channels based on protein-lipid interactions  

PubMed Central

Ion channels form a group of membrane proteins that pass ions through a pore beyond the energy barrier of the lipid bilayer. The structure of the transmembrane segment of membrane proteins is influenced by the charges and the hydrophobicity of the surrounding lipids and the pressure on its surface. A mechanosensitive channel is specifically designed to change its conformation in response to changes in the membrane pressure (tension). However, mechanosensitive channels are not the only group that is sensitive to the physical environment of the membrane: voltage-gated channels are also amenable to the lipid environment. In this article, we review the structure and gating mechanisms of the mechanosensitive channels and voltage-gated channels and discuss how their functions are affected by the physical properties of the lipid bilayer.

Yoshimura, Kenjiro; Sokabe, Masahiro

2010-01-01

66

Water in protein structure prediction  

PubMed Central

Proteins have evolved to use water to help guide folding. A physically motivated, nonpairwise-additive model of water-mediated interactions added to a protein structure prediction Hamiltonian yields marked improvement in the quality of structure prediction for larger proteins. Free energy profile analysis suggests that long-range water-mediated potentials guide folding and smooth the underlying folding funnel. Analyzing simulation trajectories gives direct evidence that water-mediated interactions facilitate native-like packing of supersecondary structural elements. Long-range pairing of hydrophilic groups is an integral part of protein architecture. Specific water-mediated interactions are a universal feature of biomolecular recognition landscapes in both folding and binding.

Papoian, Garegin A.; Ulander, Johan; Eastwood, Michael P.; Luthey-Schulten, Zaida; Wolynes, Peter G.

2004-01-01

67

BIOCHEMISTRY: TRP Ion Channels--Two Proteins in One  

NSDL National Science Digital Library

Access to the article is free, however registration and sign-in are required. It is well established that some proteins carry out more than one job in the cell, but so far, ion channels do not appear to exhibit this versatility. In their Perspective, Levitan and Cibulsky discuss a cluster of new findings showing that two members of the long TRP ion channel family, LTRPC7 and LTRPC2, are both ion channels and enzymes.

Irwin B. Levitan (University of Pennsylvania School of Medicine;Department of Neuroscience); Susan M. Cibulsky (University of Pennsylvania School of Medicine;Department of Neuroscience)

2001-08-17

68

Putting proteins back into water  

NASA Astrophysics Data System (ADS)

We introduce a simplified protein model where the solvent (water) degrees of freedom appear explicitly (although in an extremely simplified fashion). Using this model we are able to recover the thermodynamic phenomenology of proteins over a wide range of temperatures. In particular we describe both the warm and the cold protein denaturation within a single framework, while addressing important issues about the structure of model proteins.

de Los Rios, Paolo; Caldarelli, Guido

2000-12-01

69

Physiological importance of aquaporin water channels.  

PubMed

Aquaporins (AQP) are a family of at least ten homologous water transporting proteins in mammals that are expressed in many epithelial, endothelial and other tissues. Abnormalities in humans and mice lacking AQPs provide direct evidence for their physiological importance. Humans lacking AQP1 or AQP2 manifest polyuria with defective urinary concentrating ability and humans with mutations in MIP (AQP0) develop cataracts. Transgenic knockout mice lacking AQP1 or AQP3 are also remarkably polyuric, and knock-in mice expressing a mutant AQP2 have severe nephrogenic diabetes insipidus resulting in impaired neonatal survival. Other interesting phenotypes in AQP knockout mice include reduced pain sensation, reduced intraocular pressure, defective corneal fluid transport and impaired dietary fat processing (AQP1), dry skin (AQP3), protection from brain swelling and impaired hearing/vision (AQP4), and reduced fluid secretion by salivary and airway submucosal glands (AQP5). However, many phenotype studies were negative, such as normal airway/lung and skeletal muscle function despite AQP expression, indicating that tissue-specific aquaporin expression does not indicate physiological significance. The general paradigm from studies on transgenic mouse models of AQP deletion is that AQPs facilitate rapid near-isosmolar transepithelial fluid absorption / secretion, as well as rapid vectorial water movement driven by osmotic gradients. The transgenic mouse studies suggest that aquaporin inhibitors may have clinical indications as diuretics and in the treatment of cerebral edema, elevated intraocular pressure, and other conditions of abnormal fluid homeostasis. PMID:12173689

Verkman, Alan S

2002-01-01

70

Aram Chaos outflow channel: water volume and time scale  

NASA Astrophysics Data System (ADS)

The evaluation of the water volume and the formative time scale needed to carve the outflow channels represents a fundamental process for the validation of their evolutive models. We calculate these attributes for the Aram channels and we compared the results with the volume of liquid water that was produced in a single chaotization event of the Aram Chaos. The analysis suggests that a single rapid and catastrophic event is sufficient to carve the channel and the volume of flood is compatible with the volume of liquid water release in a single chaotization event of the Aram Chaos.

Roda, M.; Kleinhans, M. G.; Zegers, T. E.

2012-09-01

71

Probing Protein Channel Dynamics At The Single Molecule Level  

Microsoft Academic Search

It would be difficult to overstate the importance played by protein ion channels in cellular function. These macromolecular pores allow the passage of ions across the cellular membrane and play indispensable roles in all aspects of neurophysiology. While the patch-clamp technique continues to provide elegant descriptions of the kinetic processes involved in ion channel gating, the associated conformational changes remain

M. Ann Lee; Robert C. Dunn

1997-01-01

72

Statistical characterization and capacity of shallow water acoustic channels  

Microsoft Academic Search

This paper focuses on statistical characterization and capacity evaluation of shallow water acoustic communications channels. Wideband single-carrier and multi-carrier probe signals are employed to measure the time-varying channel response, and to estimate its statistical properties that play an important role in the design of bandwidth-efficient and power-efficient communication systems. To assess the capacity of an underwater acoustic channel, we first

Andreja Radosevic; John G. Proakis; Milica Stojanovic

2009-01-01

73

The G-protein-gated atrial K+ channel IKAch is a heteromultimer of two inwardly rectifying K+-channel proteins  

Microsoft Academic Search

Heart rate is slowed in part by acetylcholine-dependent activation of a cardiac potassium (K+) channel, IKACh. Activated muscarinic receptors stimulate lKAch via the G-protein betagamma-subunits. It has been assumed that the inwardly rectifying K+-channel gene, GIRK1, alone encodes IKAch-It is now shown that IKAch is a heteromultimer of two distinct inwardly rectifying K+-channel subunits, GIRK1 and a newly cloned member

G. Krapivinsky; E. A. Gordon; K. Wickman; B. Velimirovic; L. Krapivinsky; D. E. Clapham

1995-01-01

74

A G Protein Directly Regulates Mammalian Cardiac Calcium Channels  

Microsoft Academic Search

A possible direct effect of guanine nucleotide binding (G) proteins on calcium channels was examined in membrane patches excised from guinea pig cardiac myocytes and bovine cardiac sarcolemmal vesicles incorporated into planar lipid bilayers. The guanosine triphosphate analog, GTPgammaS, prolonged the survival of excised calcium channels independently of the presence of adenosine 3',5'-monophosphate (cAMP), adenosine triphosphate, cAMP-activated protein kinase, and

Atsuko Yatani; Juan Codina; Yutaka Imoto; John P. Reeves; Lutz Birnbaumer; Arthur M. Brown

1987-01-01

75

Calcium channel ? subunits: a functionally diverse protein family  

Microsoft Academic Search

The calcium channel ? subunits comprise an eight-member protein family that share a common topology consisting of four transmembrane\\u000a domains and intracellular N- and C-termini. Although the first ? subunit was identified as an auxiliary subunit of a voltage-dependent\\u000a calcium channel, a review of phylogenetic, bioinformatic, and functional studies indicates that they are a functionally diverse\\u000a protein family. A cluster

Ren-Shiang Chen; Tzyy-Chyn Deng; Thomas Garcia; Zachary M. Sellers; Philip M. Best

2007-01-01

76

Ca2+-activated K+ channels: from protein complexes to function.  

PubMed

Molecular research on ion channels has demonstrated that many of these integral membrane proteins associate with partner proteins, often versatile in their function, or even assemble into stable macromolecular complexes that ensure specificity and proper rate of the channel-mediated signal transduction. Calcium-activated potassium (K(Ca)) channels that link excitability and intracellular calcium concentration are responsible for a wide variety of cellular processes ranging from regulation of smooth muscle tone to modulation of neurotransmission and control of neuronal firing pattern. Most of these functions are brought about by interaction of the channels' pore-forming subunits with distinct partner proteins. In this review we summarize recent insights into protein complexes associated with K(Ca) channels as revealed by proteomic research and discuss the results available on structure and function of these complexes and on the underlying protein-protein interactions. Finally, the results are related to their significance for the function of K(Ca) channels under cellular conditions. PMID:20959620

Berkefeld, Henrike; Fakler, Bernd; Schulte, Uwe

2010-10-01

77

Marked depletion of the water-channel protein, AQP5, in the canine nictitating membrane glands might contribute to the development of KCS.  

PubMed

The objectives of this study were to investigate the normal histological localization of aquaporin (AQP) 5 protein in the lacrimal and nictitating membrane glands and to compare this localization in healthy and keratoconjunctivitis sicca (KCS) dogs. Lacrimal and nictitating membrane glands of 5 healthy Beagles and nictitating membrane glands of 5 KCS dogs (3 Beagles and 2 mongrel dogs: 0-13 years) were used for the present study. The owners of the KCS dogs did not consent to perform biopsies of the lacrimal glands. The localization and distribution of AQP5 protein were investigated by an immunohistochemical technique. In immunohistochemical staining, AQP5 was localized in the apical site of acinar epithelial and ductal epithelial cells from both the lacrimal and nictitating membrane glands in healthy dogs. However, AQP5 was not detected in the 5 KCS dogs. These results for immunohistochemical AQP5 localization might correlate with the deficiency in tear secretion found in KCS dogs. PMID:23160543

Terakado, K; Yogo, T; Kohara, Y; Soeta, S; Nezu, Y; Harada, Y; Hara, Y; Amasaki, H; Tagawa, M

2012-11-16

78

Involvement of Aquaporin5 Water Channel in Osmoregulation in Parotid Secretory Granules  

Microsoft Academic Search

Aquaporins (AQPs) are a family of channel proteins that allow water or very small solutes to pass, functioning in tissues where the rapid and regulated transport of fluid is necessary, such as the kidney, lung, and salivary glands. Aquaporin-5 (AQP5) has been demonstrated to localize on the luminal surface of the acinar cells of the salivary glands. In this paper,

M. Matsuki; S. Hashimoto; M. Shimono; M. Murakami; J. Fujita-Yoshigaki; S. Furuyama; H. Sugiya

2005-01-01

79

G protein inhibition of CaV2 calcium channels  

PubMed Central

Voltage-gated Ca2+ channels translate the electrical inputs of excitable cells into biochemical outputs by controlling influx of the ubiquitous second messenger Ca2+. As such the channels play pivotal roles in many cellular functions including the triggering of neurotransmitter and hormone release by CaV2.1 (P/Q-type) and CaV2.2 (N-type) channels. It is well established that G protein coupled receptors (GPCRs) orchestrate precise regulation neurotransmitter and hormone release through inhibition of CaV2 channels. Although the GPCRs recruit a number of different pathways, perhaps the most prominent, and certainly most studied among these is the so-called voltage-dependent inhibition mediated by direct binding of G?? to the ?1 subunit of CaV2 channels. This article will review the basics of Ca2+-channels and G protein signaling, and the functional impact of this now classical inhibitory mechanism on channel function. It will also provide an update on more recent developments in the field, both related to functional effects and crosstalk with other signaling pathways, and advances made toward understanding the molecular interactions that underlie binding of G?? to the channel and the voltage-dependence that is a signature characteristic of this mechanism.

2010-01-01

80

Anoctamin and transmembrane channel-like proteins are evolutionarily related  

PubMed Central

Anoctamin (ANO) family of proteins, consisting of 10 members in mammals, are transmembrane proteins that have Ca2+-activated Cl- channel activities. Transmembrane channel-like (TMC) family of proteins, consisting of 8 members in mammals, are also transmembrane proteins of which mutations are implicated in various human conditions, such as hearing loss and epidermodysplasia verruciformis. Here we show that ANO and TMC proteins share high sequence similarity and probably the same membrane topology, indicating that these proteins are evolutionarily related. We found many conserved amino acid residues between the two families of proteins, especially in regions spanning the transmembrane domains TM1, TM4-TM5, and TM6-TM7. These findings imply that these proteins form one large family, which we term ANO/TMC superfamily and that TMC proteins may also function as channels for Cl- or possibly other ions. The ANO/TMC superfamily proteins are present in almost all the diverse groups of eukaryotic organisms, suggesting that the proteins function in important biological processes, such as ion homeostasis, in eukaryotic cells.

HAHN, YOONSOO; KIM, DONG SEON; PASTAN, IRA H.; LEE, BYUNGKOOK

2009-01-01

81

G protein modulation of recombinant P/Q-type calcium channels by regulators of G protein signalling proteins  

PubMed Central

Fast synaptic transmission is triggered by the activation of presynaptic Ca2+ channels which can be inhibited by G?? subunits via G protein-coupled receptors (GPCR). Regulators of G protein signalling (RGS) proteins are GTPase-accelerating proteins (GAPs), which are responsible for >100-fold increases in the GTPase activity of G proteins and might be involved in the regulation of presynaptic Ca2+ channels. In this study we investigated the effects of RGS2 on G protein modulation of recombinant P/Q-type channels expressed in a human embryonic kidney (HEK293) cell line using whole-cell recordings. RGS2 markedly accelerates transmitter-mediated inhibition and recovery from inhibition of Ba2+ currents (IBa) through P/Q-type channels heterologously expressed with the muscarinic acetylcholine receptor M2 (mAChR M2). Both RGS2 and RGS4 modulate the prepulse facilitation properties of P/Q-type Ca2+ channels. G protein reinhibition is accelerated, while release from inhibition is slowed. These kinetics depend on the availability of G protein ? and ?? subunits which is altered by RGS proteins. RGS proteins unmask the Ca2+ channel ? subunit modulation of Ca2+ channel G protein inhibition. In the presence of RGS2, P/Q-type channels containing the ?2a and ?3 subunits reveal significantly altered kinetics of G protein modulation and increased facilitation compared to Ca2+ channels coexpressed with the ?1b or ?4 subunit.

Mark, Melanie D; Wittemann, Silke; Herlitze, Stefan

2000-01-01

82

Vegetation and Channel Morphology Responses to Ordinary High Water Discharge Events in Arid West Stream Channels.  

National Technical Information Service (NTIS)

Waters of the United States (WoUS) are regulated by the U.S. Army Corps of Engineers under Section 404 of the Clean Water Act (33 U.S.C. 1344). The Corps lateral jurisdictional extent in Arid West stream channels is the upper level of the ordinary high wa...

B. Allen C. Photos D. Cate L. Dixon R. Lichvar

2009-01-01

83

Structural basis of water-specific transport through the AQP1 water channel  

NASA Astrophysics Data System (ADS)

Water channels facilitate the rapid transport of water across cell membranes in response to osmotic gradients. These channels are believed to be involved in many physiological processes that include renal water conservation, neuro-homeostasis, digestion, regulation of body temperature and reproduction. Members of the water channel superfamily have been found in a range of cell types from bacteria to human. In mammals, there are currently 10 families of water channels, referred to as aquaporins (AQP): AQP0-AQP9. Here we report the structure of the aquaporin 1 (AQP1) water channel to 2.2Å resolution. The channel consists of three topological elements, an extracellular and a cytoplasmic vestibule connected by an extended narrow pore or selectivity filter. Within the selectivity filter, four bound waters are localized along three hydrophilic nodes, which punctuate an otherwise extremely hydrophobic pore segment. This unusual combination of a long hydrophobic pore and a minimal number of solute binding sites facilitates rapid water transport. Residues of the constriction region, in particular histidine 182, which is conserved among all known water-specific channels, are critical in establishing water specificity. Our analysis of the AQP1 pore also indicates that the transport of protons through this channel is highly energetically unfavourable.

Sui, Haixin; Han, Bong-Gyoon; Lee, John K.; Walian, Peter; Jap, Bing K.

2001-12-01

84

CHIP28 water channels are localized in constitutively water-permeable segments of the nephron  

PubMed Central

The sites of water transport along the nephron are well characterized, but the molecular basis of renal water transport remains poorly understood. CHIP28 is a 28-kD integral protein which was proposed to mediate transmembrane water movement in red cells and kidney (Preston, G. M., T. P. Carroll, W. B. Guggino, and P. Agre. 1992. Science [Wash. DC]. 256:385-387). To determine whether CHIP28 could account for renal epithelial water transport, we used specific polyclonal antibodies to quantitate and localize CHIP28 at cellular and subcellular levels in rat kidney using light and electron microscopy. CHIP28 comprised 3.8% of isolated proximal tubule brush border protein. Except for the first few cells of the S1 segment, CHIP28 was immunolocalized throughout the convoluted and straight proximal tubules where it was observed in the microvilli of the apical brush border and in basolateral membranes. Very little CHIP28 was detected in endocytic vesicles or other intracellular structures in proximal tubules. Uninterrupted, heavy immunostaining of CHIP28 was also observed over both apical and basolateral membranes of descending thin limbs, including both short and long loops of Henle. These nephron sites have constitutively high osmotic water permeabilities. CHIP28 was not detected in ascending thin limbs, thick ascending limbs, or distal tubules, which are highly impermeable to water. Moreover, CHIP28 was not detected in collecting duct epithelia, where water permeability is regulated by antidiuretic hormone. These determinations of abundance and structural organization provide evidence that the CHIP28 water channel is the predominant pathway for constitutive transepithelial water transport in the proximal tubule and descending limb of Henle's loop.

1993-01-01

85

Ferritin protein nanocage ion channels: gating by N-terminal extensions.  

PubMed

Ferritin protein nanocages, self-assembled from four-?-helix bundle subunits, use Fe(2+) and oxygen to synthesize encapsulated, ferric oxide minerals. Ferritin minerals are iron concentrates stored for cell growth. Ferritins are also antioxidants, scavenging Fenton chemistry reactants. Channels for iron entry and exit consist of helical hairpin segments surrounding the 3-fold symmetry axes of the ferritin nanocages. We now report structural differences caused by amino acid substitutions in the Fe(2+) ion entry and exit channels and at the cytoplasmic pores, from high resolution (1.3-1.8 ?) protein crystal structures of the eukaryotic model ferritin, frog M. Mutations that eliminate conserved ionic or hydrophobic interactions between Arg-72 and Asp-122 and between Leu-110 and Leu-134 increase flexibility in the ion channels, cytoplasmic pores, and/or the N-terminal extensions of the helix bundles. Decreased ion binding in the channels and changes in ordered water are also observed. Protein structural changes coincide with increased Fe(2+) exit from dissolved, ferric minerals inside ferritin protein cages; Fe(2+) exit from ferritin cages depends on a complex, surface-limited process to reduce and dissolve the ferric mineral. High concentrations of bovine serum albumin or lysozyme (protein crowders) to mimic the cytoplasm restored Fe(2+) exit in the variants to wild type. The data suggest that fluctuations in pore structure control gating. The newly identified role of the ferritin subunit N-terminal extensions in gating Fe(2+) exit from the cytoplasmic pores strengthens the structural and functional analogies between ferritin ion channels in the water-soluble protein assembly and membrane protein ion channels gated by cytoplasmic N-terminal peptides. PMID:22362775

Tosha, Takehiko; Behera, Rabindra K; Ng, Ho-Leung; Bhattasali, Onita; Alber, Tom; Theil, Elizabeth C

2012-02-23

86

Oxidative gating of water channels (aquaporins) in corn roots  

Microsoft Academic Search

An oxidative gating of water channels (aquaporins: AQPs) was observed in roots of corn seedlings as already found for the green alga Chara corallina . In the presence of 35 m M hydrogen peroxide (H 2 O 2 ) - a precursor of hydroxyl radicals (*OH) - half times of water flow (as measured with the aid of pressure probes)

Q. Ye; E. Steudle; QING YE

2005-01-01

87

Durable, region-specific protein patterning in microfluidic channels.  

PubMed

We present a straightforward, accessible method to covalently pattern proteins in poly(dimethyl siloxane) (PDMS) microchannels. Our approach includes (i) region-specific photografting of a layer of poly(acrylamide) (PAAm) and (ii) bioconjugation of PAAm with a desired protein. The method produces symmetric protein patterns on all channel walls, which have high specificity and pattern fidelity, are compatible with a variety of geometries and exhibit excellent longevity under shear stresses of up to 1 dyn/cm. We demonstrate the generality of the method by creating multi-protein gradients within microfluidic microchannels and by in-situ patterning of islands of multiple proteins. Protein activity was observed by the digestion of BODIPY-casein using channels patterned with trypsin. PMID:19800682

Fiddes, Lindsey K; Chan, Ho Ka C; Lau, Bryan; Kumacheva, Eugenia; Wheeler, Aaron R

2009-10-02

88

A-kinase anchoring protein 9 and IKs channel regulation.  

PubMed

A-kinase anchoring proteins (AKAPs) create compartmentalized environment inside the cell to bring various signaling molecules to their targets. In the heart, a slowly activating potassium channel (IKs) important for cardiac repolarization is tightly regulated by the sympathetic nervous system in an AKAP-dependent manner. IKs channel forms a macromolecular complex with AKAP9 and other enzymes, such as protein kinase A, phosphatase, adenylyl cyclase, and phosphodiesterase, all of which are responsible to control the phosphorylation state of the channel. Such a complex thus ensures the IKs channel to be regulated properly to maintain the normal cardiac rhythm. Disruptions of various elements of the complex have been found to cause severe pathological consequences, including the long QT syndrome. PMID:21885989

Chen, Lei; Kass, Robert S

2011-11-01

89

SARS coronavirus E protein forms cation-selective ion channels  

Microsoft Academic Search

Severe Acute Respiratory Syndrome (SARS) is caused by a novel coronavirus (SARS-CoV). Coronaviruses including SARS-CoV encode an envelope (E) protein, a small, hydrophobic membrane protein. We report that, in planar lipid bilayers, synthetic peptides corresponding to the SARS-CoV E protein forms ion channels that are more permeable to monovalent cations than to monovalent anions. Affinity-purified polyclonal antibodies recognizing the N-terminal

Lauren Wilson; Carolyn Mckinlay; Peter Gage; Gary Ewart

2004-01-01

90

Protein kinase regulation of a cloned epithelial Na+ channel  

PubMed Central

We examined the regulation of a cloned epithelial Na+ channel (alpha beta gamma-rENaC) by protein kinase A (PKA) and protein kinase C (PKC). Experiments were performed in Xenopus oocytes and in planar lipid bilayers. At a holding potential of -100 mV, amiloride-sensitive current averaged -1,279 +/- 111 nA (n = 7) in alpha beta gamma-rENaC- expressing oocytes. Currents in water-injected oocytes were essentially unresponsive to 10 microM amiloride. A 1-h stimulation of PKC with 100 nM of PMA inhibited whole-cell currents in Xenopus oocytes to 17.1 +/- 1.8, and 22.1 +/- 2.6% of control (n = 7), at holding potentials of - 100 and +40 mV, respectively. Direct injection of purified PKC resulted in similar inhibition to that observed with PMA. Additionally, the inactive phorbol ester, phorbol-12-myristate-13-acetate, 4-O-methyl, was without effect on alpha beta gamma-rENaC currents. Pretreatment with the microtubule inhibitor colchicine (100 microM) did not modify the inhibitory effect of PMA; however, pretreatment with 20 microM cytochalasin B decreased the inhibitory action of PMA to < 20% of that previously observed. In vitro-synthesized alpha beta gamma-rENaC formed an amiloride-sensitive Na(+)-selective channel when incorporated into planar lipid bilayers. Addition of PKC, diacyl-glycerol, and Mg-ATP to the side opposite that which amiloride blocked, decreased the channel's open probability (Po) from 0.44 +/- 0.06 to 0.13 +/- 0.03 (n = 9). To study the effects of PKA on alpha beta gamma-rENaC expressed in Xenopus oocytes, cAMP levels were elevated with 10 microM forskolin and 1 mM isobutyl-methyl-xanthine. This cAMP-elevating cocktail did not cause any stimulation of alpha beta gamma-rENaC currents in either the inward or outward directions. This lack of activation was also observed in oocytes preinhibited with PMA and in oocytes pretreated with cytochalasin B and PMA. Neither alpha-rENaC nor alpha beta gamma-rENaC incorporated into planar lipid bilayers could be activated with PKA and Mg-ATP added to either side of the membrane, as Po remained at 0.63 +/- 0.06 (n = 7) and 0.45 +/- 0.05 (n = 9), respectively. We conclude that: alpha beta gamma-rENaC is inhibited by PKC, and that alpha beta gamma- rENaC is not activated by PKA.

1996-01-01

91

Mutations in aquaporin-1 in phenotypically normal humans without functional CHIP water channels  

Microsoft Academic Search

The gene aquaporin-1 encodes channel-forming integral protein (CHIP), a member of a large family of water transporters found throughout nature. Three rare individuals were identified who do not express CHIP-associated Colton blood group antigens and whose red cells exhibit low osmotic water permeabilities. Genomic DNA analyses demonstrated that two individuals were homozygous for different nonsense mutations (exon deletion or frameshift),

G. M. Preston; B. L. Smith; P. Agre; M. L. Zeidel; J. J. Moulds

1994-01-01

92

Protein 4.1 and the control of ion channels.  

PubMed

The classical function of 4.1R in red blood cells is to contribute to the mechanochemical properties of the membrane by promoting the interaction between spectrin and actin. More recently, it has been recognized that 4.1R is required for the stable cell surface accumulation of a number of erythrocyte membrane proteins. 4.1R is one member of the mammalian 4.1 family - the others being 4.1N, 4.1G and 4.1B - and is expressed in many cell types other than erythrocytes. Recently we have examined the phenotype of hearts from 4.1R knockout mice. Although they had a generally normal morphology, these hearts exhibited bradycardia, and prolongation of both action potentials and QT intervals. Electrophysiological analysis revealed anomalies in a range of ion channel activities. In addition, the immunoreactivity of voltage-gated Na(+) channel NaV1.5 was reduced, indicating a role for 4.1R in the cellular accumulation of this ion channel. 4.1 proteins also have roles in the accumulation of at least two other classes of ion channel. In epithelia, 4.1 interacts with the store-operated channel TRPC4. In neurons, the ligand-gated channels GluR1 and GluR4 require 4.1 proteins for cell surface accumulation. The spectrum of transmembrane proteins that bind to 4.1 proteins overlaps with that of ankyrin. A hypothesis to investigate in the future is that differential regulation of 4.1 and ankyrins (e.g. by PIP(2)) allows highly selective control of cell surface accumulation and transport activity of a specific range of ion channels. PMID:19272819

Baines, Anthony J; Bennett, Pauline M; Carter, Edward W; Terracciano, Cesare

2009-03-09

93

Potassium channels and epilepsy: evidence that the epileptogenic toxin, dendrotoxin, binds to potassium channel proteins.  

PubMed

Dendrotoxin-I, a component of the venom of the black mamba snake, Dendroaspis polylepsis, was used to affinity purify a potassium channel from bovine brain. This dendrotoxin-I binding protein was composed of several subunits with molecular weights of 35,000, 38,000, 42,000 and 74,000. Partial sequence resulting from Edman degradation of the N-terminus of the 74 kDa subunit was identical to the predicted amino acid sequence of the N-terminus of a protein encoded by a mouse/rat homologue of the Shaker gene family of potassium channels, MK2/RBK2 (RCK5). Polyclonal antibodies raised against synthetic peptides derived from the predicted amino acid sequence of another member of this family, MK1, recognized this 74 kDa subunit. Due to extensive amino acid sequence identity between MK2 and MK1, it is likely that antibodies recognized epitopes common to both. Thus, from an immunological standpoint, either MK1, MK2, or both channel proteins could have been present in this 74 kDa band on protein blots. Closely related K+ channels in bovine brain could have copurified based on their affinity for dendrotoxin-I (DTX-I). DTX-I was shown to inhibit MK1 currents in a time and voltage independent fashion. Physiological and molecular evidence indicates the existence of many types of DTX sensitive potassium channels in the mammalian brain, however, our protein sequencing of the 74 kDa subunit has detected the presence of only one unique N-terminal sequence, identical to MK2. The possible reason for the appearance of this discrepancy is discussed. This paper represents the first report identifying one dendrotoxin binding protein in bovine brain tissue (BK2) as a delayed rectifier type of potassium channel. PMID:1815606

Newitt, R A; Houamed, K M; Rehm, H; Tempel, B L

1991-01-01

94

Numerical investigation of deep water circulation in the Faroese Channels  

NASA Astrophysics Data System (ADS)

The overflow of dense water from the Nordic Seas through the Faroese Channels is investigated numerically using the Massachusetts Institute of Technology General Circulation Model. The model is forced by the removal of a barrier that separates different water masses in the bottom layer of the Faroe-Shetland Channel at the north-eastern boundary. An analysis of the output reveals that during its adjustment in the rotating channel the propagating flow is unstable and forms cyclonic and anti-cyclonic eddies in the Faroese Channels. The life-time of the cyclonic eddy is about 10 days, but an anti-cyclonic eddy that is formed upstream of the sill crest of the Faroe Bank Channel has a longer life-time. However, after 50 days it eventually loses its structure below 400 m due to the decay of a counter-rotating current. In the upper 400 m layer this anti-cyclonic eddy remains persistent for longer. Observational evidence of the eddy is confirmed by the tracks of experimental drifters released in the area and by the temperature and salinity fields observed in the Faroese Channels. The pinching of isotherms along the Wyville Thomson Ridge results in the concentration of cold water on the southern side of the Faroese Channels that overflows into the Rockall Trough. The model results demonstrate that the main part of the cold water outflows through the Faroe Bank Channel, rather than across the Wyville Thompson Ridge, due to Earth rotation. The apparent similarity of modelled temperature, salinity and velocity sections to recent measurements in this area adds confidence to these results.

Stashchuk, Nataliya; Vlasenko, Vasiliy; Sherwin, Toby J.

2011-07-01

95

Mercury Inhibits the L170C Mutant of Aquaporin Z by Making Waters Clog the Water Channel  

PubMed Central

We conduct in silico experiments of the L170C mutant of the E. coli aquaporin Z (AQPZ) with and without mercury bonded to Residue Cys 170. We find that bonding mercury to Cys 170 does not induce consequential structural changes to the protein. We further find that mercury does not stick in the middle of the water channel to simply occlude water permeation, but resides on the wall of the water pore. However, we observe that the water permeation coefficient of L170C-Hg+ (with one mercury ion bonded to Cys 170) is approximately half of that of the mercury-free L170C. We examine the interactions between the mercury ion and the waters in its vicinity and find that five to six waters are strongly attracted by the mercury ion, occluding the space of the water channel. Therefore we conclude that mercury, at low concentration, inhibits AQPZ-L170C mutant by making water molecules clog the water channel.

Zhang, Yubo; Cui, Yubao; Chen, L. Y.

2011-01-01

96

Erosive dynamics of channels incised by subsurface water flow  

NASA Astrophysics Data System (ADS)

We propose a dynamical model for channels incised into an erodible bed by subsurface water flow. The model is validated by the time-resolved topographic measurements of channel growth in a laboratory-scale experiment. Surface heights in the experiment are measured via a novel laser-aided imaging technique. The erosion rate in the model is composed of diffusive and advective components as well as a simple driving term due to the seeping water. Steady driving conditions may exist whenever channels are incised into a flat and level erodible bed by a water table replenished via steady (on average) rainfall. Under such steady driving conditions, the model predicts an asymptotically self-similar growing shape for the channel transects. Conversely, given a transect shape that evolved under steady driving conditions and an estimate of the erosion rate at the bottom of the channel, granular transport coefficients can be inferred from the static channel shape. We report an estimate of these transport coefficients for a system of ravines incised into unconsolidated sand in the Apalachicola River basin, Florida.

Lobkovsky, Alexander E.; Smith, Braunen E.; Kudrolli, Arshad; Mohrig, David C.; Rothman, Daniel H.

2007-09-01

97

Travelling long waves in water channels of specific configurations  

NASA Astrophysics Data System (ADS)

The rigorous travelling wave solution in water channels of rectangular cross-section with variable depth and width is obtained in the framework of shallow water theory. The differential equation connecting depth and width of the channel for the case of the non-reflecting wave propagation is derived. It is shown that a number of geometries and configurations, which allow non-reflecting wave propagation, is unlimited. So, the effect of very long-distance wave propagation is rather common and can play an important role in the interpretation of sometimes observed extreme inundation caused by storm surges, tsunami and coastal rogue waves.

Pelinovsky, Efim; Didenkulova, Ira; Pelinovsky, Dmitry; Tyugin, Dmitry; Giniyatullin, Arat

2013-04-01

98

Engineering Proteins for Custom Inhibition of CaV Channels  

PubMed Central

The influx of Ca2+ ions through voltage-dependent calcium (CaV) channels links electrical signals to physiological responses in all excitable cells. Not surprisingly, blocking CaV channel activity is a powerful method to regulate the function of excitable cells, and this is exploited for both physiological and therapeutic benefit. Nevertheless, the full potential for CaV channel inhibition is not being realized by currently available small molecule blockers or second messenger modulators due to limitations in targeting them either to defined groups of cells in an organism or to distinct sub-cellular regions within a single cell. Here, we review early efforts to engineer protein molecule blockers of CaV channels to fill this crucial niche. This technology would greatly expand the toolbox available to physiologists studying the biology of excitable cells at the cellular and systems level.

Xu, Xianghua; Colecraft, Henry M.

2010-01-01

99

Distribution of mRNA encoding the FA-CHIP water channel in amphibian tissues: Effects of salt adaptation  

Microsoft Academic Search

A water channel, the frog aquaporin-CHIP (FA-CHIP) was recently cloned from Rana esculenta urinary bladder. The 28.9 kDa encoded protein shows 78.8%, 77.4%, 42.4% and 35.6% identity with rat CHIP28, human CHIP28, rat WCH-CD and ?-TIP, other members of the new transmembrane water channel family (Aquaporin-CHIP). We have now studied membranes from different frog (R. esculenta) organs employing semiquantitative PCR

L. Abrami; C. Capurro; C. Ibarra; M. Parisi; J.-M. Buhler; P. Ripoche

1995-01-01

100

Seasonal Variations of Fat, Protein, and Moisture in Channel Catfish.  

National Technical Information Service (NTIS)

The seasonal variations of fat, protein and moisture of age class II channel catfish fed a pelleted diet were determined. Results suggested that fish fed supplemental diets deposited an average of 210 kilocalories as fat during a 132-day feeding period. T...

C. Suppes O. W. Tiemeier C. W. Deyoe

1968-01-01

101

Regulation of the epithelial sodium channel by accessory proteins.  

PubMed Central

The epithelial sodium channel (ENaC) is of fundamental importance in the control of sodium fluxes in epithelial cells. Modulation of sodium reabsorption through the distal nephron ENaC is an important component in the overall control of sodium balance, blood volume and thereby of blood pressure. This is clearly demonstrated by rare genetic disorders of sodium-channel activity (Liddle's syndrome and pseudohypoaldosteronism type 1), associated with contrasting effects on blood pressure. The mineralocorticoid aldosterone is a well-established modulator of sodium-channel activity. Considerable insight has now been gained into the intracellular signalling pathways linking aldosterone-mediated changes in gene transcription with changes in ion transport. Activating pathways include aldosterone-induced proteins and especially the serum- and glucocorticoid-inducible kinase (SGK) and the small G-protein, K-Ras 2A. Targeting of the ENaC for endocytosis and degradation is now emerging as a major mechanism for the down-regulation of channel activity. Several proteins acting in concert are an intrinsic part of this process but Nedd4 (neural precursor cell expressed developmentally down-regulated 4) is of central importance. Other mechanisms known to interact with ENaC and affect sodium transport include channel-activating protease 1 (CAP-1), a membrane-anchored protein, and the cystic fibrosis transmembrane regulator. The implications of research on accessory factors controlling ENaC activity are wide-ranging. Understanding cellular mechanisms controlling ENaC activity may provide a more detailed insight not only of ion-channel abnormalities in cystic fibrosis but also of the link between abnormal renal sodium transport and essential hypertension.

Gormley, Kelly; Dong, Yanbin; Sagnella, Giuseppe A

2003-01-01

102

Analysis of experimental shallow water network channel and theoretical channel model  

Microsoft Academic Search

This paper describes the testing of an experimental water acoustic network communication that was conducted at the North Sea, Netherlands. The North Sea is a shallow channel that exhibits multipath propagation that results in signal fading and phase fluctuations at the receiver. The Doppler effect is another phenomenon that is observed due the movement of both the source and the

H. K. Yeo; B. S. Sharif; A. E. Adams; O. R. Hinton

2000-01-01

103

Qumran: Water Channel ad Cave Entrance, Dead Sea Scrolls Area  

Microsoft Academic Search

This photograph was taken in Qumran, the area where in 1947 (or late 1946) the Dead Sea Scrolls were discovered by three Bedouin shepherds. The caves are located about eight miles south of Jericho, in present day Israel. In this picture a sign can be seen that says ‘Water Channel’ and a cave entrance can be seen in the hills.

Chet Smolski

1980-01-01

104

TRIP Database: a manually curated database of protein-protein interactions for mammalian TRP channels.  

PubMed

Transient receptor potential (TRP) channels are a superfamily of Ca(2+)-permeable cation channels that translate cellular stimuli into electrochemical signals. Aberrant activity of TRP channels has been implicated in a variety of human diseases, such as neurological disorders, cardiovascular disease and cancer. To facilitate the understanding of the molecular network by which TRP channels are associated with biological and disease processes, we have developed the TRIP (TRansient receptor potential channel-Interacting Protein) Database (http://www.trpchannel.org), a manually curated database that aims to offer comprehensive information on protein-protein interactions (PPIs) of mammalian TRP channels. The TRIP Database was created by systematically curating 277 peer-reviewed literature; the current version documents 490 PPI pairs, 28 TRP channels and 297 cellular proteins. The TRIP Database provides a detailed summary of PPI data that fit into four categories: screening, validation, characterization and functional consequence. Users can find in-depth information specified in the literature on relevant analytical methods and experimental resources, such as gene constructs and cell/tissue types. The TRIP Database has user-friendly web interfaces with helpful features, including a search engine, an interaction map and a function for cross-referencing useful external databases. Our TRIP Database will provide a valuable tool to assist in understanding the molecular regulatory network of TRP channels. PMID:20851834

Shin, Young-Cheul; Shin, Soo-Yong; So, Insuk; Kwon, Dongseop; Jeon, Ju-Hong

2010-09-17

105

Protein Rearrangements Underlying Slow Inactivation of the Shaker K+ Channel  

PubMed Central

Voltage-dependent ion channels transduce changes in the membrane electric field into protein rearrangements that gate their transmembrane ion permeation pathways. While certain molecular elements of the voltage sensor and gates have been identified, little is known about either the nature of their conformational rearrangements or about how the voltage sensor is coupled to the gates. We used voltage clamp fluorometry to examine the voltage sensor (S4) and pore region (P-region) protein motions that underlie the slow inactivation of the Shaker K+ channel. Fluorescent probes in both the P-region and S4 changed emission intensity in parallel with the onset and recovery of slow inactivation, indicative of local protein rearrangements in this gating process. Two sequential rearrangements were observed, with channels first entering the P-type, and then the C-type inactivated state. These forms of inactivation appear to be mediated by a single gate, with P-type inactivation closing the gate and C-type inactivation stabilizing the gate's closed conformation. Such a stabilization was due, at least in part, to a slow rearrangement around S4 that stabilizes S4 in its activated transmembrane position. The fluorescence reports of S4 and P-region fluorophore are consistent with an increased interaction of the voltage sensor and inactivation gate upon gate closure, offering insight into how the voltage-sensing apparatus is coupled to a channel gate.

Loots, E.; Isacoff, E.Y.

1998-01-01

106

Channel Extension in Deep-Water Distributive Systems  

NASA Astrophysics Data System (ADS)

The cyclic nature of channel and lobe formation in submarine fans is the result of the unstable and ephemeral nature of newly formed distributary channels. Avulsion cycles are initiated as unconfined sheet flow immediately following avulsion followed by stages of channel incision and extension, deposition of channel mouth deposits, and often channel backfilling. In contrast with those in alluvial and deltaic environments, avulsion cycles in submarine fans are relatively poorly understood due to the difficulty of observing deep ocean processes, either over short timescales needed to measure the hydrodynamics of active turbidity currents, or over longer timescales needed for the morphodynamic evolution of individual distributary channels and avulsion events. Here we report the results of over 80 experiments in a 5m x 3m x1m deep tank using saline (NaCl) density flows carrying low-density plastic sediment (SG 1.5) flowing down an inclined ramp. These experiments were designed to investigate trends observed in earlier self-organized experimental submarine fans with well-developed avulsion cycles, in which distributive lobes were observed to form on relatively high slopes. In particular, we were interested in investigating the relationship between channel extension length (distance from the inlet to the point where the flow becomes de-channelized, transitioning into a mouth-bar/lobe) and slope. The results of the experiments are clear but counter-intuitive. Channels appear to extend in discrete segments and channel extension length is inversely related to slope over a wide range of slopes (5-17 degrees). In addition, channel extension seems largely independent of inlet flow density (salt concentration) over the experimental range (10-24 g/cc). Measurements of densimetric Froude number (Fr') indicate Fr' increases downstream to near critical conditions at the channel lobe transition. Our preliminary interpretation is that distributary channels become unstable due to acceleration to Fr'-critical conditions and the formation of a depositional hydraulic jump, which perturbs sediment transport and ends channel extension. Similar morphodynamic length scale controls are observed in shallow water fan-delta experiments (e.g., SAFL DB-03) and in 2-D depositional cyclic steps. The experiments seem to explain two interesting observations from the earlier self-organized fan experiments and from real submarine fans. Firstly, the observation of 'perched' fills at the steep entrances to salt withdrawal minibasins (e.g., in the Gulf of Mexico) suggesting higher sedimentation rates (or inefficient sediment transport) on higher slopes (initially higher than at the slope break downstream). Secondly, strong progradation as the fan evolves and slope decreases in 'perched' fans suggests increasing flow efficiency on lower slopes, at least over a certain window of parameter space. Apparently deep water systems have a tendency to self-regulate even when flows differ significantly in initial density. The observed modulation to Fr'-critical flow appears to be an important control on length scales in deep- water distributive channel systems, potentially explaining strong deepwater progradation or 'delta-like' patterns that have remained paradoxical. Near critical conditions have been inferred from observations of many active submarine fans but the extent to which these results from conservative density currents apply to non-conservative and potentially 'ignitive' turbidity currents is the subject of ongoing investigation.

Hoyal, D. C.; Sheets, B. A.

2007-12-01

107

Voltage Gated Ion Channel Function: Gating, Conduction, and the Role of Water and Protons  

SciTech Connect

Ion channels, which are found in every biological cell, regulate the concentration of electrolytes, and are responsible for multiple biological functions, including in particular the propagation of nerve impulses. The channels with the latter function are gated (opened) by a voltage signal, which allows Na+ into the cell and K+ out. These channels have several positively charged amino acids on a transmembrane domain of their voltage sensor, and it is generally considered, based primarily on two lines of experimental evidence, that these charges move with respect to the membrane to open the channel. At least three forms of motion, with greatly differing extents and mechanisms of motion, have been proposed. There is a “gating current”, a capacitative current preceding the channel opening, that corresponds to several charges (for one class of channel typically 12–13) crossing the membrane field, which may not require protein physically crossing a large fraction of the membrane. The coupling to the opening of the channel would in these models depend on the motion. The conduction itself is usually assumed to require the “gate” of the channel to be pulled apart to allow ions to enter as a section of the protein partially crosses the membrane, and a selectivity filter at the opposite end of the channel determines the ion which is allowed to pass through. We will here primarily consider K+ channels, although Na+ channels are similar. We propose that the mechanism of gating differs from that which is generally accepted, in that the positively charged residues need not move (there may be some motion, but not as gating current). Instead, protons may constitute the gating current, causing the gate to open; opening consists of only increasing the diameter at the gate from approximately 6 Å to approximately 12 Å. We propose in addition that the gate oscillates rather than simply opens, and the ion experiences a barrier to its motion across the channel that is tuned by the water present within the channel. Our own quantum calculations as well as numerous experiments of others are interpreted in terms of this hypothesis. It is also shown that the evidence that supports the motion of the sensor as the gating current can also be consistent with the hypothesis we present.

Kariev, Alisher M.; Green, Michael E.

2012-02-26

108

Filter gate closure inhibits ion but not water transport through potassium channels.  

PubMed

The selectivity filter of K(+) channels is conserved throughout all kingdoms of life. Carbonyl groups of highly conserved amino acids point toward the lumen to act as surrogates for the water molecules of K(+) hydration. Ion conductivity is abrogated if some of these carbonyl groups flip out of the lumen, which happens (i) in the process of C-type inactivation or (ii) during filter collapse in the absence of K(+). Here, we show that K(+) channels remain permeable to water, even after entering such an electrically silent conformation. We reconstituted fluorescently labeled and constitutively open mutants of the bacterial K(+) channel KcsA into lipid vesicles that were either C-type inactivating or noninactivating. Fluorescence correlation spectroscopy allowed us to count both the number of proteoliposomes and the number of protein-containing micelles after solubilization, providing the number of reconstituted channels per proteoliposome. Quantification of the per-channel increment in proteoliposome water permeability with the aid of stopped-flow experiments yielded a unitary water permeability pf of (6.9 ± 0.6) × 10(-13) cm(3)?s(-1) for both mutants. "Collapse" of the selectivity filter upon K(+) removal did not alter pf and was fully reversible, as demonstrated by current measurements through planar bilayers in a K(+)-containing medium to which K(+)-free proteoliposomes were fused. Water flow through KcsA is halved by 200 mM K(+) in the aqueous solution, which indicates an effective K(+) dissociation constant in that range for a singly occupied channel. This questions the widely accepted hypothesis that multiple K(+) ions in the selectivity filter act to mutually destabilize binding. PMID:23754382

Hoomann, Torben; Jahnke, Nadin; Horner, Andreas; Keller, Sandro; Pohl, Peter

2013-06-10

109

High-Density Reconstitution of Functional Water Channels into Vesicular and Planar Block Copolymer Membranes  

PubMed Central

The exquisite selectivity and unique transport properties of membrane proteins can be harnessed for a variety of engineering and biomedical applications if suitable membranes can be produced. Amphiphilic block copolymers (BCPs), developed as stable lipid analogs, form membranes that functionally incorporate membrane proteins and are ideal for such applications. While high protein density and planar membrane morphology are most desirable, BCP–membrane protein aggregates have so far been limited to low protein densities in either vesicular or bilayer morphologies. Here, we used dialysis to reproducibly form planar and vesicular BCP membranes with a high density of reconstituted aquaporin-0 (AQP0) water channels. We show that AQP0 retains its biological activity when incorporated at high density in BCP membranes, and that the morphology of the BCP–protein aggregates can be controlled by adjusting the amount of incorporated AQP0. We also show that BCPs can be used to form two-dimensional crystals of AQP0.

2012-01-01

110

Bimodal modulation of the botulinum neurotoxin protein-conducting channel  

PubMed Central

Clostridium botulinum neurotoxin (BoNT) is the causative agent of botulism, a neuroparalytic disease. We describe here a semisynthetic strategy to identify inhibitors based on toosendanin, a traditional Chinese medicine reported to protect from BoNT intoxication. Using a single molecule assay of BoNT serotypes A and E light chain (LC) translocation through the heavy chain (HC) channel in neurons, we discovered that toosendanin and its tetrahydrofuran analog selectively arrest the LC translocation step of intoxication with subnanomolar potency, and increase the unoccluded HC channel propensity to open with micromolar efficacy. The inhibitory profile on LC translocation is accurately recapitulated in 2 different BoNT intoxication assays, namely the mouse protection and the primary rat spinal cord cell assays. Toosendanin has an unprecedented dual mode of action on the protein-conducting channel acting as a cargo-dependent inhibitor of translocation and as cargo-free channel activator. These results imply that the bimodal modulation by toosendanin depends on the dynamic interactions between channel and cargo, highlighting their tight interplay during the progression of LC transit across endosomes.

Fischer, Audrey; Nakai, Yuya; Eubanks, Lisa M.; Clancy, Colin M.; Tepp, William H.; Pellett, Sabine; Dickerson, Tobin J.; Johnson, Eric A.; Janda, Kim D.; Montal, Mauricio

2009-01-01

111

Regulator of G-protein signaling 14 protein modulates Ca²+ influx through Cav1 channels.  

PubMed

Calcium flux through L-type voltage-activated calcium (Cav1) channels is crucial for regulating brain functions including memory formation and behavior. Alterations in Ca²+ homeostasis have been linked to many cognitive disorders, and understanding the regulation of this process is crucial for their remedy. Therefore, here, we have evaluated the effect of a multifunctional protein known to be involved in memory functions called regulator of G-protein signaling 14 (RGS-14) on Cav1 channel activity in neuronal cell lines NG108-15 and SH-SY5Y. RGS-14 protein produced significant reduction in Ca²+ influx in both cell lines and this effect was dependent on nifedipine-sensitive Cav1 channels. Thus, our results provide evidence supporting the idea that RGS-14 may facilitate the cognitive processing by modulating Cav1 channel-mediated intracellular Ca²+ transients. PMID:20842066

Martín-Montañez, Elisa; Acevedo, Maria José; López-Téllez, Juan Félix; Duncan, Raymond Scott; Mateos, Antonio González; Pavía, José; Koulen, Peter; Khan, Zafar U

2010-11-17

112

Channelopathies from mutations in the cardiac sodium channel protein complex.  

PubMed

The cardiac sodium current underlies excitability in heart, and inherited abnormalities of the proteins regulating and conducting this current cause inherited arrhythmia syndromes. This review focuses on inherited mutations in non-pore forming proteins of sodium channel complexes that cause cardiac arrhythmia, and the deduced mechanisms by which they affect function and dysfunction of the cardiac sodium current. Defining the structure and function of these complexes and how they are regulated will contribute to understanding the possible roles for this complex in normal and abnormal physiology and homeostasis. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes". PMID:23557754

Adsit, Graham S; Vaidyanathan, Ravi; Galler, Carla M; Kyle, John W; Makielski, Jonathan C

2013-04-01

113

Pressure measurements on a pitching airfoil in a water channel  

Microsoft Academic Search

Measurements of unsteady pressures over a symmetric NACA 0015 airfoil performing pitching maneuvers are reported. The tests were performed in an open-surface water channel specially constructed for this purpose. The design of the apparatus allowed the pressure measurements to be made to a very high degree of spatial and temporal resolution. Reynolds numbers in the range of 5.2 x 10(exp

Rand N. Conger; B. R. Ramaprian

1994-01-01

114

Aquaporin water channels: unanswered questions and unresolved controversies  

Microsoft Academic Search

The long-standing biophysical question of how water crosses plasma membranes has been answered by the recent discovery of the aquaporins. Identification of this large family of membrane water-transport proteins has generated new questions about the physiological functions, tissue distributions, and regulatory mechanisms of individual aquaporins. The fast pace of developments in this field has also resulted in major discrepancies in

Peter Agre; Dennis Brown; Søren Nielsen

1995-01-01

115

Mutations in aquaporin-1 in phenotypically normal humans without functional CHIP water channels  

SciTech Connect

The gene aquaporin-1 encodes channel-forming integral protein (CHIP), a member of a large family of water transporters found throughout nature. Three rare individuals were identified who do not express CHIP-associated Colton blood group antigens and whose red cells exhibit low osmotic water permeabilities. Genomic DNA analyses demonstrated that two individuals were homozygous for different nonsense mutations (exon deletion or frameshift), and the third had a missense mutation encoding a nonfunctioning CHIP molecule. Surprisingly, none of the three suffers any apparent clinical consequence, which raises questions about the physiological importance of CHIP and implies that other mechanisms may compensate for its absence. 20 refs., 3 figs., 1 tab.

Preston, G.M.; Smith, B.L.; Agre, P. [Johns Hopkins Univ. School of Medicine, Baltimore, MD (United States); Zeidel, M.L. [Univ. of Pittsburgh, Pittsburgh, PA (United States); Moulds, J.J. [Gamma Biologicals, Houston, TX (United States)

1994-09-09

116

Novel Channel Enzyme Fusion Proteins Confer Arsenate Resistance*  

PubMed Central

Steady exposure to environmental arsenic has led to the evolution of vital cellular detoxification mechanisms. Under aerobic conditions, a two-step process appears most common among microorganisms involving reduction of predominant, oxidized arsenate (H2AsVO4?/HAsVO42?) to arsenite (AsIII(OH)3) by a cytosolic enzyme (ArsC; Escherichia coli type arsenate reductase) and subsequent extrusion via ArsB (E. coli type arsenite transporter)/ACR3 (yeast type arsenite transporter). Here, we describe novel fusion proteins consisting of an aquaglyceroporin-derived arsenite channel with a C-terminal arsenate reductase domain of phosphotyrosine-phosphatase origin, providing transposable, single gene-encoded arsenate resistance. The fusion occurred in actinobacteria from soil, Frankia alni, and marine environments, Salinispora tropica; Mycobacterium tuberculosis encodes an analogous ACR3-ArsC fusion. Mutations rendered the aquaglyceroporin channel more polar resulting in lower glycerol permeability and enhanced arsenite selectivity. The arsenate reductase domain couples to thioredoxin and can complement arsenate-sensitive yeast strains. A second isoform with a nonfunctional channel may use the mycothiol/mycoredoxin cofactor pool. These channel enzymes constitute prototypes of a novel concept in metabolism in which a substrate is generated and compartmentalized by the same molecule. Immediate diffusion maintains the dynamic equilibrium and prevents toxic accumulation of metabolites in an energy-saving fashion.

Wu, Binghua; Song, Jie; Beitz, Eric

2010-01-01

117

Hydration of proteins: excess partial volumes of water and proteins.  

PubMed

High precision densitometry was applied to study the hydration of proteins. The hydration process was analyzed by the simultaneous monitoring of the excess partial volumes of water and the proteins in the entire range of water content. Five unrelated proteins (lysozyme, chymotrypsinogen A, ovalbumin, human serum albumin, and ?-lactoglobulin) were used as models. The obtained data were compared with the excess partial enthalpies of water and the proteins. It was shown that the excess partial quantities are very sensitive to the changes in the state of water and proteins. At the lowest water weight fractions (w(1)), the changes of the excess functions can mainly be attributed to water addition. A transition from the glassy to the flexible state of the proteins is accompanied by significant changes in the excess partial quantities of water and the proteins. This transition appears at a water weight fraction of 0.06 when charged groups of proteins are covered. Excess partial quantities reach their fully hydrated values at w(1) > 0.5 when coverage of both polar and weakly interacting surface elements is complete. At the highest water contents, water addition has no significant effect on the excess quantities. At w(1) > 0.5, changes in the excess functions can solely be attributed to changes in the state of the proteins. PMID:22380610

Sirotkin, Vladimir A; Komissarov, Igor A; Khadiullina, Aigul V

2012-03-22

118

Identification and characterization of the channel-forming protein in the cell wall of Corynebacterium amycolatum.  

PubMed

The mycolic-acid layer of certain gram-positive bacteria, the mycolata, represents an additional permeability barrier for the permeation of small water-soluble solutes. Consequently, it was shown in recent years that the mycolic acid layer of individual bacteria of the group mycolata contains pores, called porins, for the passage of hydrophilic solutes. Corynebacterium amycolatum, a pathogenic Corynebacterium species, belongs to the Corynebacteriaceae family but it lacks corynomycolic acids in its cell wall. Despite the absence of corynomycolic acids the cell wall of C. amycolatum contains a cation-selective cell wall channel, which may be responsible for the limited permeability of the cell wall of C. amycolatum. Based on partial sequencing of the protein responsible for channel formation derived from C. amycolatum ATCC 49368 we were able to identify the gene coram0001_1986 within the known genome sequence of C. amycolatum SK46 that codes for the cell wall channel. The corresponding gene of C. amycolatum ATCC 49368 was cloned into the plasmid pXHis for its expression in Corynebacterium glutamicum ?porA?porH. Biophysical characterization of the purified protein (PorAcoram) suggested that coram0001_1986 is indeed the gene coding for the pore-forming protein PorAcoram in C. amycolatum ATCC 49368. The protein belongs to the DUF (Domains of Unknown Function) 3068 superfamily of proteins, mainly found in bacteria from the family Corynebacteriaceae. The nearest relative to PorAcoram within this family is an ORF which codes for PorAcres, which was also recognized in reconstitution experiments as a channel-forming protein in Corynebacterium resistens. PMID:23811360

Soltan Mohammadi, Nafiseh; Mafakheri, Samaneh; Abdali, Narges; Bárcena-Uribarri, Iván; Tauch, Andreas; Benz, Roland

2013-06-27

119

Formation of Droplets of Different Compositions in Microfluidic Channels and Applications to Protein Crystallization  

NASA Astrophysics Data System (ADS)

This presentation reports characterization and applications of formation of nanoliter droplets of different compositions in microfluidic channels. In this method several different aqueous streams were injected into a flow of an immiscible oil to form droplets in the microfluidic channels. The conditions required to form the steady flow of the droplets in a microchannel were characterized as a function of the capillary number (Ca) and water fraction. Four flow regimes that were defined by Ca and water fraction were observed and characterized. The compositions of the adjacent droplets were found lineally related and allowed indexing compositions of droplets. We also demonstrated applications of these phenomena by conducting protein crystallization in droplets in the microchannels under the condition of microbatch and vapor diffusion, with characterization by on-chip x-ray diffraction.

Zheng, Bo

2005-03-01

120

Template-assembled melittin: structural and functional characterization of a designed, synthetic channel-forming protein.  

PubMed Central

Template-assembled proteins (TASPs) comprising 4 peptide blocks, each of either the natural melittin sequence (melittin-TASP) or of a truncated melittin sequence (amino acids 6-26, melittin6-26-TASP), C-terminally linked to a (linear or cyclic) 10-amino acid template were synthesized and characterized, structurally by CD, by fluorescence spectroscopy, and by monolayer experiments, and functionally, by electrical conductance measurements on planar bilayers and release experiments on dye-loaded vesicles. Melittin-TASP and the truncated analogue preferentially adopt alpha-helical structures in methanol (56% and 52%, respectively) as in lipid membranes. Unlike in methanol, the melittin-TASP self-aggregates in water. On an air-water interface, the differently sized molecules can be self-assembled and compressed to a compact structure with a molecular area of around 600 A2, compatible with a 4-helix bundle preferentially oriented perpendicular to the interface. The proteins reveal a strong affinity for lipid membranes. A partition coefficient of 1.5 x 10(9) M-1 was evaluated from changes of the Trp fluorescence spectra of the TASP in water and in the lipid bilayer. In planar lipid bilayers, TASP molecules are able to form defined ion channels, exhibiting a small single-channel conductance of 7 pS (in 1 M NaCl). With increasing protein concentration in the lipid bilayer, additional, larger conductance states of up to 1 nS were observed. These states are likely to be formed by aggregated TASP structures as inferred from a strongly voltage-dependent channel activity on membranes of large area. In this respect, melittin-TASP reveals channel features of the native peptide, but with a considerably lower variation in the size of the channel states. Compared to the free peptide, template-assembled melittin has a much higher membrane activity: it is about 100 times more effective in channel formation and 20 times more effective in releasing dye molecules from lipid vesicles. This demonstrates that the lytic properties are not solely related to channel formation.

Pawlak, M.; Meseth, U.; Dhanapal, B.; Mutter, M.; Vogel, H.

1994-01-01

121

Evidence for Water-Permeable Channels in Auditory Hair Cells in the Leopard Frog  

PubMed Central

Auditory hair cells in the amphibian papilla (APHCs) of the leopard frog, Rana pipiens pipiens, have a significantly higher permeability to water than that observed in mammalian hair cells. The insensitivity of water permeability in frog hair cells to extracellular mercury suggests that an amphibian homologue of the water channel aquaporin-4 (AQP4) may mediate water transport in these cells. Using immunocytochemistry, we show that an AQP4-like protein is found in APHCs. Rabbit anti-AQP4 antibody was used in multiple-immunohistochemical staining experiments along with AP hair cell and hair bundle markers in leopard frog and mouse tissue. AQP4-immunoreactivity was found in the basal and apical poles of the APHCs and shows uniform immunoreactivity. This study provides the first identification and localization of an AQP4-like protein in the amphibian inner ear. We also report a more direct measure of hyperosmotically-induced volume changes in APHCs that confirms previous findings. The presence of water channels in anuran APHCs constitutes a novel physiological difference between amphibian and mammalian hair cell structure and function.

Miller, Mia E.; Nasiri, Arian K.; Farhangi, Peyman O.; Farahbakhsh, Nasser A.; Lopez, Ivan A.; Narins, Peter M.; Simmons, Dwayne D.

2012-01-01

122

Approaches to the characterization of membrane channel proteins (porins) by UV MALDI-MS  

NASA Astrophysics Data System (ADS)

Suitable detergents and sample preparation conditions have been characterized for the analysis of membrane channel proteins (porins) by matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS). Using the matrix [alpha]-cyano-4-hydroxycinnamic acid (HCCA), the best results were obtained with non-ionic detergents such as n-octylglucopyranoside. Ionic detergents such as sodium dodecylsulphate (SDS) had the most adverse effects on MALDI-MS analyses both for water-soluble and for membrane proteins. For the analysis of membrane proteins, a sample preparation procedure by ultrasonic treatment has been developed which yielded high signal intensities, particularly for proteins for which MALDI spectra, were difficult to obtain by the standard dried-droplet technique. For some high molecular weight porins, successful MALDI-MS analyses were only possible with the ultrasonication procedure.

Schnaible, Volker; Michels, Jenny; Zeth, Kornelius; Freigang, Jorg; Welte, Wolfram; Buhler, Stefan; Glocker, Michael O.; Przybylski, Michael

1997-12-01

123

Water-protein interactions from high-resolution protein crystallography.  

PubMed Central

To understand the role of water in life at molecular and atomic levels, structures and interactions at the protein-water interface have been investigated by cryogenic X-ray crystallography. The method enabled a much clearer visualization of definite hydration sites on the protein surface than at ambient temperature. Using the structural models of proteins, including several hydration water molecules, the characteristics in hydration structures were systematically analysed for the amount, the interaction geometries between water molecules and proteins, and the local and global distribution of water molecules on the surface of proteins. The tetrahedral hydrogen-bond geometry of water molecules in bulk solvent was retained at the interface and enabled the extension of a three-dimensional chain connection of a hydrogen-bond network among hydration water molecules and polar protein atoms over the entire surface of proteins. Networks of hydrogen bonds were quite flexible to accommodate and/or to regulate the conformational changes of proteins such as domain motions. The present experimental results may have profound implications in the understanding of the physico-chemical principles governing the dynamics of proteins in an aqueous environment and a discussion of why water is essential to life at a molecular level.

Nakasako, Masayoshi

2004-01-01

124

Water-protein interactions from high-resolution protein crystallography.  

PubMed

To understand the role of water in life at molecular and atomic levels, structures and interactions at the protein-water interface have been investigated by cryogenic X-ray crystallography. The method enabled a much clearer visualization of definite hydration sites on the protein surface than at ambient temperature. Using the structural models of proteins, including several hydration water molecules, the characteristics in hydration structures were systematically analysed for the amount, the interaction geometries between water molecules and proteins, and the local and global distribution of water molecules on the surface of proteins. The tetrahedral hydrogen-bond geometry of water molecules in bulk solvent was retained at the interface and enabled the extension of a three-dimensional chain connection of a hydrogen-bond network among hydration water molecules and polar protein atoms over the entire surface of proteins. Networks of hydrogen bonds were quite flexible to accommodate and/or to regulate the conformational changes of proteins such as domain motions. The present experimental results may have profound implications in the understanding of the physico-chemical principles governing the dynamics of proteins in an aqueous environment and a discussion of why water is essential to life at a molecular level. PMID:15306376

Nakasako, Masayoshi

2004-08-29

125

Rapid aquaporin translocation regulates cellular water flow: mechanism of hypotonicity-induced subcellular localization of aquaporin 1 water channel.  

PubMed

The control of cellular water flow is mediated by the aquaporin (AQP) family of membrane proteins. The structural features of the family and the mechanism of selective water passage through the AQP pore are established, but there remains a gap in our knowledge of how water transport is regulated. Two broad possibilities exist. One is controlling the passage of water through the AQP pore, but this only has been observed as a phenomenon in some plant and microbial AQPs. An alternative is controlling the number of AQPs in the cell membrane. Here, we describe a novel pathway in mammalian cells whereby a hypotonic stimulus directly induces intracellular calcium elevations through transient receptor potential channels, which trigger AQP1 translocation. This translocation, which has a direct role in cell volume regulation, occurs within 30 s and is dependent on calmodulin activation and phosphorylation of AQP1 at two threonine residues by protein kinase C. This direct mechanism provides a rationale for the changes in water transport that are required in response to constantly changing local cellular water availability. Moreover, because calcium is a pluripotent and ubiquitous second messenger in biological systems, the discovery of its role in the regulation of AQP translocation has ramifications for diverse physiological and pathophysiological processes, as well as providing an explanation for the rapid regulation of water flow that is necessary for cell homeostasis. PMID:22334691

Conner, Matthew T; Conner, Alex C; Bland, Charlotte E; Taylor, Luke H J; Brown, James E P; Parri, H Rheinallt; Bill, Roslyn M

2012-02-09

126

Hydration of proteins: excess partial enthalpies of water and proteins.  

PubMed

Isothermal batch calorimetry was applied to study the hydration of proteins. The hydration process was analyzed by the simultaneous monitoring of the excess partial enthalpies of water and the proteins in the entire range of water content. Four unrelated proteins (lysozyme, chymotrypsinogen A, human serum albumin, and ?-lactoglobulin) were used as models. The excess partial quantities are very sensitive to the changes in the state of water and proteins. At the lowest water weight fractions (w(1)), the changes of the excess thermochemical functions can mainly be attributed to water addition. A transition from the glassy to the flexible state of the proteins is accompanied by significant changes in the excess partial quantities of water and the proteins. This transition appears at a water weight fraction of 0.06 when charged groups of proteins are covered. Excess partial quantities reach their fully hydrated values at w(1) > 0.5 when coverage of both polar and weakly interacting surface elements is complete. At the highest water contents, water addition has no significant effect on the excess thermochemical quantities. At w(1) > 0.5, changes in the excess functions can solely be attributed to changes in the state of the proteins. PMID:22044193

Sirotkin, Vladimir A; Khadiullina, Aigul V

2011-11-29

127

Expression of aquaporin water channels in mouse spinal cord  

Microsoft Academic Search

Aquaporins (AQPs) are membrane proteins involved in water transport in many fluid-transporting tissues. Aquaporins AQP1, AQP4, and AQP9 have been identified in brain and hypothesized to participate in brain water homeostasis. Here we use reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry to describe the expression and immunolocalization of AQPs in adult mouse spinal cord. AQP4 was expressed in

K. OSHIO; D. K. BINDER; B. YANG; S Schecter; A. S Verkman; G. T Manley

2004-01-01

128

Heat transfer in protein-water interfaces.  

PubMed

We investigate using transient non-equilibrum molecular dynamics simulation the temperature relaxation process of three structurally different proteins in water, namely; myoglobin, green fluorescence protein (GFP) and two conformations of the Ca(2+)-ATPase protein. By modeling the temperature relaxation process using the solution of the heat diffusion equation we compute the thermal conductivity and thermal diffusivity of the proteins, as well as the thermal conductance of the protein-water interface. Our results indicate that the temperature relaxation of the protein can be described using a macroscopic approach. The protein-water interface has a thermal conductance of the order of 100-270 MW K(-1) m(-2), characteristic of water-hydrophilic interfaces. The thermal conductivity of the proteins is of the order of 0.1-0.2 W K(-1) m(-1) as compared with approximately 0.6 W K(-1) m(-1) for water, suggesting that these proteins can develop temperature gradients within the biomolecular structures that are larger than those of aqueous solutions. We find that the thermal diffusivity of the transmembrane protein, Ca(2+)-ATPase is about three times larger than that of myoglobin or GFP. Our simulation shows that the Kapitza length of these structurally different proteins is of the order of 1 nm, showing that the protein-water interface should play a major role in defining the thermal relaxation of biomolecules. PMID:20126777

Lervik, Anders; Bresme, Fernando; Kjelstrup, Signe; Bedeaux, Dick; Miguel Rubi, J

2010-01-11

129

Molecular mechanism of H+ conduction in the single-file water chain of the gramicidin channel.  

PubMed Central

The conduction of protons in the hydrogen-bonded chain of water molecules (or "proton wire") embedded in the lumen of gramicidin A is studied with molecular dynamics free energy simulations. The process may be described as a "hop-and-turn" or Grotthuss mechanism involving the chemical exchange (hop) of hydrogen nuclei between hydrogen-bonded water molecules arranged in single file in the lumen of the pore, and the subsequent reorganization (turn) of the hydrogen-bonded network. Accordingly, the conduction cycle is modeled by two complementary steps corresponding respectively to the translocation 1) of an ionic defect (H+) and 2) of a bonding defect along the hydrogen-bonded chain of water molecules in the pore interior. The molecular mechanism and the potential of mean force are analyzed for each of these two translocation steps. It is found that the mobility of protons in gramicidin A is essentially determined by the fine structure and the dynamic fluctuations of the hydrogen-bonded network. The translocation of H+ is mediated by spontaneous (thermal) fluctuations in the relative positions of oxygen atoms in the wire. In this diffusive mechanism, a shallow free-energy well slightly favors the presence of the excess proton near the middle of the channel. In the absence of H+, the water chain adopts either one of two polarized configurations, each of which corresponds to an oriented donor-acceptor hydrogen-bond pattern along the channel axis. Interconversion between these two conformations is an activated process that occurs through the sequential and directional reorientation of water molecules of the wire. The effect of hydrogen-bonding interactions between channel and water on proton translocation is analyzed from a comparison to the results obtained previously in a study of model nonpolar channels, in which such interactions were missing. Hydrogen-bond donation from water to the backbone carbonyl oxygen atoms lining the pore interior has a dual effect: it provides a coordination of water molecules well suited both to proton hydration and to high proton mobility, and it facilitates the slower reorientation or turn step of the Grotthuss mechanism by stabilizing intermediate configurations of the hydrogen-bonded network in which water molecules are in the process of flipping between their two preferred, polarized states. This mechanism offers a detailed molecular model for the rapid transport of protons in channels, in energy-transducing membrane proteins, and in enzymes.

Pomes, Regis; Roux, Benoit

2002-01-01

130

O^- channels of Dissociative Electron Attachment to water and heavy water molecules  

NASA Astrophysics Data System (ADS)

A COLTRIM technique is modified to measure the kinetic energy and angular distribution of O^- ions arising from dissociative electron attachment to water and heavy water molecules. A low energy pulsed electron, an effusive water target, a pulsed extraction plate are used in combination with the COLTRIMS spectrometer. The spectrometer carries an electrostatic lens system to compensate the effusiveness of the target. This technique is applied to study the O^- channels in the three Feshbach resonances of water and heavy water anion. The measured kinetic energy release will give the energy partitioning among the fragments, and the means to identify the two-body and three-body breakup channels. The angular distribution of the O^- ions with respect to the electron beam is found to reflect well the breakup dynamics of the H2O^- at the dissociation. The experimental results are compared with the theoretical predictions.

Adaniya, Hidehito; Rudek, Benedikt; Osipov, Timur; Lee, Sun; Weber, Thorsten; Hertlein, Marcus; Schoeffler, Markus; Prior, Mike; Belkacem, Ali

2009-05-01

131

The role of transmembrane channel-like proteins in the operation of hair cell mechanotransducer channels.  

PubMed

Sound stimuli elicit movement of the stereocilia that make up the hair bundle of cochlear hair cells, putting tension on the tip links connecting the stereocilia and thereby opening mechanotransducer (MT) channels. Tmc1 and Tmc2, two members of the transmembrane channel-like family, are necessary for mechanotransduction. To assess their precise role, we recorded MT currents elicited by hair bundle deflections in mice with null mutations of Tmc1, Tmc2, or both. During the first postnatal week, we observed a normal MT current in hair cells lacking Tmc1 or Tmc2; however, in the absence of both isoforms, we recorded a large MT current that was phase-shifted 180°, being evoked by displacements of the hair bundle away from its tallest edge rather than toward it as in wild-type hair cells. The anomalous MT current in hair cells lacking Tmc1 and Tmc2 was blocked by FM1-43, dihydrostreptomycin, and extracellular Ca(2+) at concentrations similar to those that blocked wild type. MT channels in the double knockouts carried Ca(2+) with a lower permeability than wild-type or single mutants. The MT current in double knockouts persisted during exposure to submicromolar Ca(2+), even though this treatment destroyed the tip links. We conclude that the Tmc isoforms do not themselves constitute the MT channel but are essential for targeting and interaction with the tip link. Changes in the MT conductance and Ca(2+) permeability observed in the absence of Tmc1 mutants may stem from loss of interaction with protein partners in the transduction complex. PMID:24127526

Kim, Kyunghee X; Beurg, Maryline; Hackney, Carole M; Furness, David N; Mahendrasingam, Shanthini; Fettiplace, Robert

2013-10-14

132

Water channel (aquaporin 1) expression and distribution in mammary carcinomas and glioblastomas.  

PubMed

The aquaporins represent a family of transmembrane water channel proteins that are widely distributed in various tissues throughout the body and play a major role in transcellular and transepithelial water movement. Most tumors have been shown to exhibit high vascular permeability and high interstitial fluid pressure, but the transport pathways for water within tumors remain unknown. In this study, we examined the distribution of the aquaporin 1 (AQP1) water channel protein in several types of transplanted tumor. Two mammary carcinomas, MCaIV and R3230AC, and three glioblastomas, HGL21, U87, and F98, were implanted in rats and mice. Two sites of implantation in rodents were chosen: a cranial window (CW) region and a subcutaneous (SC) region. Tissues were studied using immunoblot analysis and immunofluorescence staining. In the mammary carcinomas, AQP1 was localized in vascular structures; no differences between CW and SC regions were observed. Among the three glioblastomas, HGL21 and U87 exhibited similar AQP1 localization in vascular structures, whereas the center of F98 did not show vascular staining. Cell membranes of normal epithelial cells did not show AQP1 expression, while membranes of most tumor cells exhibited significant AQP1 expression. Interestingly, however, HGL21 and F98 in the CW locations showed no AQP1 expression on tumor cell membranes. These results show that the AQP1 water channel is heterogeneously expressed in tumor cells and their vasculature, and that the level of expression is determined not only by the specific cellular origin of the tumor, but also by the location of the tumor in the host animal. PMID:10458924

Endo, M; Jain, R K; Witwer, B; Brown, D

1999-09-01

133

Emerging roles for G protein-gated inwardly rectifying potassium (GIRK) channels in health and disease  

Microsoft Academic Search

G protein-gated inwardly rectifying potassium (GIRK) channels hyperpolarize neurons in response to activation of many different G protein-coupled receptors and thus control the excitability of neurons through GIRK-mediated self-inhibition, slow synaptic potentials and volume transmission. GIRK channel function and trafficking are highly dependent on the channel subunit composition. Pharmacological investigations of GIRK channels and studies in animal models suggest that

Christian Lüscher; Paul A. Slesinger

2010-01-01

134

Microfabricated Patch Clamp Electrodes for Improved Ion Channel Protein Measurements  

NASA Astrophysics Data System (ADS)

Ion channels are trans-membrane proteins that underlie many cell functions including hormone and neurotransmitter release, muscle contraction and cell signaling cascades. Ion channel proteins are commonly characterized via the patch clamp method in which an extruded glass tube containing ionic solution, manipulated by an expert technician, is brought into contact with a living cell to record ionic current through the cell membrane. Microfabricated planar patch electrodes, micromolded in the silicone elastomer poly-dimethylsiloxane (PDMS) from microlithographically patterned structures, have been developed that improve on this method. Microfabrication techniques allow arrays of patch electrodes to be fabricated, increasing the throughput of the measurement technique. Planar patch electrodes readily allow the automation of cell sealing, further increasing throughput. Microfabricated electrode arrays may be readily integrated with microfluidic structures to allow fast, in situ solution exchange. Miniaturization of the electrode geometry should increase both the signal to noise and the bandwidth of the measurement. Microfabricated patch electrode arrays have been fabricated and measurements have been taken.

Klemic, James; Klemic, Kathryn; Reed, Mark; Sigworth, Frederick

2002-03-01

135

A-Kinase Anchoring Protein Targeting of Protein Kinase A and Regulation of HERG Channels  

Microsoft Academic Search

Adrenergic stimulation of the heart initiates a signaling cascade in cardiac myocytes that increases the concentration of\\u000a cAMP. Although cAMP elevation may occur over a large area of a target-organ cell, its effects are often more restricted due\\u000a to local concentration of its main effector, protein kinase A (PKA), through A-kinase anchoring proteins (AKAPs). The HERG\\u000a potassium channel, which produces

Yan Li; Jakub Sroubek; Yamini Krishnan; Thomas V. McDonald

2008-01-01

136

Pressure measurements on a pitching airfoil in a water channel  

NASA Astrophysics Data System (ADS)

Measurements of unsteady pressures over a symmetric NACA 0015 airfoil performing pitching maneuvers are reported. The tests were performed in an open-surface water channel specially constructed for this purpose. The design of the apparatus allowed the pressure measurements to be made to a very high degree of spatial and temporal resolution. Reynolds numbers in the range of 5.2 x 10(exp 4) to 2.2 x 10(exp 5) were studied. Although the results qualitatively agreed with earlier studies performed at similar Reynolds numbers, the magnitudes of pressure and aerodynamic forces measured were observed to be much larger than those measured in ealier pitchup studies. They were found, in fact, to be closer to those obtained in some recent high-Reynolds-number experiments. This interesting behavior, which was suspected to be caused by the relatively high freestream turbulence level in the water channel, was explored in some detail. In addition, several issues like the quasisteady and dynamic effects of the pitching process are discussed. The experimental data are all archived and are available for use as a database.

Conger, Rand N.; Ramaprian, B. R.

1994-01-01

137

Effects of water temperature and dissolved oxygen on daily feed consumption, feed utilization and growth of channel catfish ( Ictalurus punctatus)  

Microsoft Academic Search

Feed intake (FI), feed efficiency (FE), protein efficiency ratio (PER) and weight gain (WG) of juvenile channel catfish initially weighing 15.0±0.23 g (10–12 cm initial total length) were evaluated under three regimes of time-varying water temperature (mean daily water temperature for Stoneville, MS, USA; mean +3; and, mean ?3°C) and three of dissolved oxygen (DO; 100, 70 and 30% air

J. Alejandro Buentello; Delbert M Gatlin; William H Neill

2000-01-01

138

Time-correlation analysis of simulated water motion in flexible and rigid gramicidin channels.  

PubMed Central

Molecular dynamics simulations have been done on a system consisting of the polypeptide membrane channel former gramicidin, plus water molecules in the channel and caps of waters at the two ends of the channel. In the absence of explicit simulation of the surrounding membrane, the helical form of the channel was maintained by artificial restraints on the peptide motion. The characteristic time constant of the artificial restraint was varied to assess the effect of the restraints on the channel structure and water motions. Time-correlation analysis was done on the motions of individual channel waters and on the motions of the center of mass of the channel waters. It is found that individual water molecules confined in the channel execute higher frequency motions than bulk water, for all degrees of channel peptide restraint. The center-of-mass motion of the chain of channel waters (which is the motion that is critical for transmembrane transport, due to the mandatory single filing of water in the channel) does not exhibit these higher frequency motions. The mobility of the water chain is dramatically reduced by holding the channel rigid. Thus permeation through the channel is not like flow through a rigid pipe; rather permeation is facilitated by peptide motion. For the looser restraints we used, the mobility of the water chain was not very much affected by the degree of restraint. Depending on which set of experiments is considered, the computed mobility of our water chain in the flexible channel is four to twenty times too high to account for the experimentally measured resistance of the gramicidin channel to water flow. From this result it appears likely that the peptide motions of an actual gramicidin channel embedded in a lipid membrane may be more restrained than in our flexible channel model, and that these restraints may be a significant modulator of channel permeability. For the completely rigid channel model the "trapping" of the water molecules in preferred positions throughout the molecular dynamics run precludes a reasonable assessment of mobility, but it seems to be quite low.

Chiu, S W; Jakobsson, E; Subramaniam, S; McCammon, J A

1991-01-01

139

Matrix protein from Escherichia coli outer membranes forms voltage-controlled channels in lipid bilayers.  

PubMed Central

Matrix protein from Escherichia coli was integrated into planar lipid bilayers. The incorporated protein generates aqueous channels across these membranes. Channels are induced irreversibly by voltage, and their number is proportional to the protein content of the membrane and stays constant over hours. They are uniform in size, with a diameter of about 1 nm and a single-channel conductance of 0.14 nS in 0.1 M NaCl. In addition to ionic conductance, the channels allow free diffusion of small, uncharged molecules. Channels assume either an open or a closed state. Membrane potentials shift this two-state equilibrium distribution in favor of closed channels, an observation that explains both negative resistance and inactivation at high potentials. Channels are not randomly distributed in the membrane but interact cooperatively within aggregates. The smallest entity inducible consists of three channels.

Schindler, H; Rosenbusch, J P

1978-01-01

140

Regulation of an Aplysia Bag Cell Neuron Cation Channel by Closely Associated Protein Kinase A and a Protein Phosphatase  

Microsoft Academic Search

Ion channel regulation by closely associated kinases or phosphatases has emerged as a key mechanism for orchestrating neuromodula- tion. An exemplary case is the nonselective cation channel that drives the afterdischarge in Aplysia bag cell neurons. Initial studies showed that this channel is modulated by both a closely associated PKC and a serine\\/threonine protein phosphatase (PP). In excised, inside-out patches,

Neil S. Magoski

2004-01-01

141

Water transport across biological membranes: Overton, water channels, and peritoneal dialysis.  

PubMed

Peritoneal dialysis involves diffusive and convective transports and osmosis through the highly vascularized peritoneal membrane. Several lines of evidence have demonstrated that the water channel aquaporin-1 (AQP1) corresponds to the ultrasmall pore predicted by the modelization of peritoneal transport. Proof-of-principle studies have shown that upregulation of the expression of AQP1 in peritoneal capillaries is reflected by increased water permeability and ultrafiltration, without affecting the osmotic gradient and the permeability for small solutes. Inversely, studies in Aqp1 mice have shown that haplo-insufficiency in AQP1 is reflected by significant attenuation of water transport. Recent studies have identified lead compounds that could act as agonists of aquaporins, as well as putative binding sites and potential mechanisms of gating the water channel. By modulating water transport, these pharmacological agents could have clinically relevant effects in targeting specific tissues or disease states. These studies on the peritoneal membrane also provide an experimental framework to investigate the role of water channels in the endothelium and various cell types. PMID:21510484

Devuyst, O

2010-01-01

142

Detection Of Regolith Buried Water Stream Channels On Mars With The Help Of Synthetic Aperture Radar  

Microsoft Academic Search

The major problem of Mars research is search of water on its surface. Biological life is connected to water. In this connection the intense interest represents detection of water stream channels, which in the past flew on Mars. In these areas the petrified rests of the former life on Mars may be found out. Now these channels may be under

O. N. Rzhiga

2004-01-01

143

LEA proteins prevent protein aggregation due to water stress.  

PubMed

LEA (late embryogenesis abundant) proteins in both plants and animals are associated with tolerance to water stress resulting from desiccation and cold shock. However, although various functions of LEA proteins have been proposed, their precise role has not been defined. Recent bioinformatics studies suggest that LEA proteins might behave as molecular chaperones, and the current study was undertaken to test this hypothesis. Recombinant forms of AavLEA1, a group 3 LEA protein from the anhydrobiotic nematode Aphelenchus avenae, and Em, a group 1 LEA protein from wheat, have been subjected to functional analysis. Heat-stress experiments with citrate synthase, which is susceptible to aggregation at high temperatures, suggest that LEA proteins do not behave as classical molecular chaperones, but they do exhibit a protective, synergistic effect in the presence of the so-called chemical chaperone, trehalose. In contrast, both LEA proteins can independently protect citrate synthase from aggregation due to desiccation and freezing, in keeping with a role in water-stress tolerance; similar results were obtained with lactate dehydrogenase. This is the first evidence of anti-aggregation activity of LEA proteins due to water stress. Again, a synergistic effect of LEA and trehalose was observed, which is significant given that non-reducing disaccharides are known to accumulate during dehydration in plants and nematodes. A model is proposed whereby LEA proteins might act as a novel form of molecular chaperone, or 'molecular shield', to help prevent the formation of damaging protein aggregates during water stress. PMID:15631617

Goyal, Kshamata; Walton, Laura J; Tunnacliffe, Alan

2005-05-15

144

Role of aquaporin water channels in eye function  

Microsoft Academic Search

The aquaporins (AQPs) are a family of more than 10 homologous water transporting proteins expressed in many mammalian epithelia and endothelia. At least five AQPs are expressed in the eye: AQP0 (MIP) in lens fiber, AQP1 in cornea endothelium, ciliary and lens epithelia and trabecular meshwork, AQP3 in conjunctiva, AQP4 in ciliary epithelium and retinal Müller cells, and AQP5 in

A. S. Verkman

2003-01-01

145

More than just water channels: unexpected cellular roles of aquaporins  

Microsoft Academic Search

Aquaporins (AQPs) are membrane proteins that transport water and, in some cases, also small solutes such as glycerol. AQPs are expressed in many fluid-transporting tissues, such as kidney tubules and glandular epithelia, as well as in non-fluid-transporting tissues, such as epidermis, adipose tissue and astroglia. Their classical role in facilitating trans-epithelial fluid transport is well understood, as in the urinary

A. S. Verkman

2005-01-01

146

dSLo Interacting Protein 1, a Novel Protein That Interacts with Large-Conductance Calcium-Activated Potassium Channels  

Microsoft Academic Search

Large-conductance calcium-activated potassium channels (BK channels) are activated by depolarized membrane potential and elevated levels of intracellular calcium. BK channel activity underlies the fast afterhyperpolarization that follows an action potential and attenuates neurotransmitter and hormone secre- tion. Using a modified two-hybrid approach, the interaction trap, we have identified a novel protein from Drosophila, dSLIP1 (dSLo interacting protein), which specifically interacts

Xiao-ming Xia; Birgit Hirschberg; Sarah Smolik; Michael Forte; John P. Adelman

147

Mechanism of Inhibition of Cyclic Nucleotide-gated Channel by Protein Tyrosine Kinase Probed with Genistein  

Microsoft Academic Search

Rod cyclic nucleotide-gated (CNG) channels are modulated by changes in tyrosine phosphorylation catalyzed by protein tyrosine kinases (PTKs) and phosphatases (PTPs). We used genistein, a PTK inhibitor, to probe the interaction between the channel and PTKs. Previously, we found that in addition to inhibiting tyrosine phosphorylation of the rod CNG channel a -subunit (RET a ), genistein triggers a noncatalytic

Elena Molokanova; Richard H. Kramer

2001-01-01

148

Vasopressin Increases Water Permeability of Kidney Collecting Duct by Inducing Translocation of Aquaporin-CD Water Channels to Plasma Membrane  

Microsoft Academic Search

Water excretion by the kidney is regulated by the peptide hormone vasopressin. Vasopressin increases the water permeability of the renal collecting duct cells, allowing more water to be reabsorbed from collecting duct urine to blood. Despite long-standing interest in this process, the mechanism of the water permeability increase has remained undetermined. Recently, a molecular water channel (AQP-CD) has been cloned

Soren Nielsen; Chung-Lin Chou; David Marples; Erik I. Christensen; Bellamkonda K. Kishore; Mark A. Knepper

1995-01-01

149

The LRRC26 protein selectively alters the efficacy of BK channel activators.  

PubMed

Large conductance, Ca(2+)-activated K channel proteins are involved in a wide range of physiological activities, so there is considerable interest in the pharmacology of large conductance calcium-activated K (BK) channels. One potent activator of BK channels is mallotoxin (MTX), which produces a very large hyperpolarizing shift of the voltage gating of heterologously expressed BK channels and causes a dramatic increase in the activity of BK channels in human smooth muscle cells. However, we found that MTX shifted the steady-state activation of BK channels in native parotid acinar cells by only 6 mV. This was not because the parotid BK isoform (parSlo) is inherently insensitive to MTX as MTX shifted the activation of heterologously expressed parSlo channels by 70 mV. Even though MTX had a minimal effect on steady-state activation of parotid BK channels, it produced an approximate 2-fold speeding of the channel-gating kinetics. The BK channels in parotid acinar cells have a much more hyperpolarized voltage activation range than BK channels in most other cell types. We found that this is probably attributable to an accessory protein, LRRC26, which is expressed in parotid glands: expressed parSlo + LRRC26 channels were resistant to the actions of MTX. Another class of BK activators is the benzimidazalones that includes 1,3-dihydro-1-(2-hydroxy-5-(trifluoromethyl)phenyl)-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619). Although the LRRC26 accessory protein strongly inhibited the ability of MTX to activate BK channels, we found that it had only a small effect on the action of NS-1619 on BK channels. Thus, the LRRC26 BK channel accessory protein selectively alters the pharmacology of BK channels. PMID:21984254

Almassy, Janos; Begenisich, Ted

2011-10-07

150

The LRRC26 Protein Selectively Alters the Efficacy of BK Channel Activators  

PubMed Central

Large conductance, Ca2+-activated K channel proteins are involved in a wide range of physiological activities, so there is considerable interest in the pharmacology of large conductance calcium-activated K (BK) channels. One potent activator of BK channels is mallotoxin (MTX), which produces a very large hyperpolarizing shift of the voltage gating of heterologously expressed BK channels and causes a dramatic increase in the activity of BK channels in human smooth muscle cells. However, we found that MTX shifted the steady-state activation of BK channels in native parotid acinar cells by only 6 mV. This was not because the parotid BK isoform (parSlo) is inherently insensitive to MTX as MTX shifted the activation of heterologously expressed parSlo channels by 70 mV. Even though MTX had a minimal effect on steady-state activation of parotid BK channels, it produced an approximate 2-fold speeding of the channel-gating kinetics. The BK channels in parotid acinar cells have a much more hyperpolarized voltage activation range than BK channels in most other cell types. We found that this is probably attributable to an accessory protein, LRRC26, which is expressed in parotid glands: expressed parSlo + LRRC26 channels were resistant to the actions of MTX. Another class of BK activators is the benzimidazalones that includes 1,3-dihydro-1-(2-hydroxy-5-(trifluoromethyl)phenyl)-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619). Although the LRRC26 accessory protein strongly inhibited the ability of MTX to activate BK channels, we found that it had only a small effect on the action of NS-1619 on BK channels. Thus, the LRRC26 BK channel accessory protein selectively alters the pharmacology of BK channels.

Almassy, Janos

2012-01-01

151

Expression of the aquaporin 8 water channel in a rat salivary epithelial cell.  

PubMed

Aquaporins are a family of water channels considered to play an important role in fluid transport across plasma membranes. Among the reported isoforms, relatively little is known about the functional role of aquaporin 8 (AQP8), and there are no cell lines known to express the AQP8 protein. We report here that the rat submandibular epithelial cell line, SMIE, expresses AQP8. Using RT-PCR, the presence of mRNA for AQP8 was demonstrated in these cells. Confocal immunofluorescence experiments revealed that the AQP8 protein is primarily present in the apical membranes of SMIE cells. When grown as a polarized monolayer on collagen coated polycarbonate filters, and exposed on their apical surface to different hyperosmotic (440, 540, or 640 mOsm) solutions, net fluid movement across SMIE cells was 8-25-fold that seen under isosmotic conditions. Similarly, when grown on coverslips and then exposed to a hypertonic solution, SMIE cells shrunk as a function of time. Together, these results suggest that SMIE cells endogenously express functional AQP8 water channels. PMID:12012329

Hoque, A T M Shamsul; Yamano, Seiichi; Liu, Xibao; Swaim, William D; Goldsmith, Corinne M; Delporte, Christine; Baum, Bruce J

2002-06-01

152

The Use of Stream Channels to Deliver Stored Water: The Possibility of Interference by Third Parties.  

National Technical Information Service (NTIS)

The report is addressed to one aspect of the adaptation of old water rights law to contemporary conditions: legal issues associated with the use of stream channels to deliver stored water from impoundments. The report identifies three possible threats of ...

D. R. Gill

1969-01-01

153

Vascular amyloid alters astrocytic water and potassium channels in mouse models and humans with Alzheimer's disease  

PubMed Central

The neurovascular unit (NVU) comprises cerebral blood vessels and surrounding astrocytes, neurons, perivascular microglia and pericytes. Astrocytes associated with the NVU are responsible for maintaining cerebral blood flow and ionic and osmotic balances in the brain. A significant proportion of individuals with Alzheimer’s disease (AD) have vascular amyloid deposits (cerebral amyloid angiopathy, CAA) that contribute to the heterogeneous nature of the disease. To determine whether NVU astrocytes are affected by the accumulation of amyloid at cerebral blood vessels we examined astrocytic markers in four transgenic mouse models of amyloid deposition. These mouse models represent mild CAA, moderate CAA with disease progression to tau pathology and neuron loss, severe CAA and severe CAA with disease progression to tau pathology and neuron loss. We found that CAA and disease progression both resulted in distinct NVU astrocytic changes. CAA causes a loss of apparent GFAP-positive astrocytic end-feet and loss of water channels (aquaporin 4) localized to astrocytic end feet. The potassium channels Kir4.1-an inward rectifying potassium channel and BK – a calcium-sensitive large-conductance potassium channel were also lost. The anchoring protein, dystrophin 1, is common to these channels and was reduced in association with CAA. Disease progression was associated with a phenotypic switch in astrocytes indicated by a loss of GFAP-positive cells and a gain of S100?-positive cells. Aquaporin 4, Kir4.1 and dystrophin 1 were also reduced in autopsied brain tissue from individuals with AD that also display moderate and severe CAA. Together, these data suggest that damage to the neurovascular unit may be a factor in the pathogenesis of Alzheimer’s disease.

Wilcock, Donna M.; Vitek, Michael P.; Colton, Carol A.

2009-01-01

154

Protein Kinase Modulation of Dendritic K Channels in Hippocampus Involves a Mitogen-Activated Protein Kinase Pathway  

Microsoft Academic Search

We investigated mitogen-activated protein kinase (MAPK) mod- ulation of dendritic, A-type K channels in CA1 pyramidal neurons in the hippocampus. Activation of cAMP-dependent protein kinase A (PKA) and protein kinase C (PKC) leads to an increase in the amplitude of backpropagating action potentials in distal dendrites through downregulation of transient K channels in CA1 pyramidal neurons in the hippocampus. We

Li-Lian Yuan; J. Paige Adams; Michael Swank; J. David Sweatt; Daniel Johnston

2002-01-01

155

EFFECT OF ELEVATED WATER TEMPERATURE ON MACRO-INVERTEBRATE COMMUNITIES IN OUTDOOR EXPERIMENTAL CHANNELS  

EPA Science Inventory

Macroinvertebrates were sampled monthly from December 1976 to September 1977 in two 520 m long outdoor experimental channels. One channel was maintained at ambient seasonal Mississippi River water temperatures and the other 10C higher. Maximum water temperature reached 31.0C in t...

156

Diffusion, molecular separation, and drug delivery from lipid mesophases with tunable water channels.  

PubMed

Lyotropic liquid crystals characterized by a bicontinuous cubic phase (BCP) have a structure characterized by interpenetrated water channels following triply periodic minimal surfaces, which can be stable in excess water conditions and thus suitable in a multitude of applications. The control of the water channels size in these systems has a direct impact on their use for drug delivery, crystallization, and membrane separation processes. In this work we carry out systematic diffusion studies to show how the control on the water channel dimensions directly correlates with the release and separation performance of bicontinuous cubic phases. Specifically, we tune the water channels diameter of the monolinolein/water system by adding different amounts of sucrose stearate, which, having hydration-enhancing properties, can shift the boundaries of the phase diagram. We then design a model bicontinuous cubic phase lipidic membrane of the Im3m space group, having a sugar ester to monolinolein ratio of 20%, and we follow the diffusion within its water channels, by using molecules that differ systematically in size and molecular conformation, and we demonstrate, for each class of molecules, a diffusion-enhanced process upon increase of the water channel diameter. Finally, we also show the ability of the bicontinuous cubic phase to efficiently and selectively separate nanoparticles of a target size, by choosing an amount of sucrose stearate for which the water channel diameter and the nanoparticle dimensions match, demonstrating the possible use of these systems as filtering membranes of tunable molecular cutoff. PMID:23116138

Negrini, Renata; Mezzenga, Raffaele

2012-11-08

157

Corynebacterium diphtheriae: Identification and Characterization of a Channel-Forming Protein in the Cell Wall  

Microsoft Academic Search

The cell wall fraction of the gram-positive, nontoxic Corynebacterium diphtheriae strain C8r() Tox ( ATCC 11913) contained a channel-forming protein, as judged from reconstitution experiments with artificial lipid bilayer experiments. The channel-forming protein was present in detergent-treated cell walls and in extracts of whole cells obtained using organic solvents. The protein had an apparent molecular mass of about 66 kDa

Bettina Schiffler; Enrico Barth; Mamadou Daffe; Roland Benz

2007-01-01

158

Kinetic modeling of Na + -induced, G??-dependent activation of G protein-gated K + channels  

Microsoft Academic Search

G protein-activated K+(GIRK) channels are activated by numerous neurotransmitters that act on Gi\\/o proteins, via a direct interaction with the G?? subunit of G proteins. In addition, GIRK channels are positively regulated\\u000a by intracellular Na+ via a direct interaction (fast pathway) and via a G??-dependent mechanism (slow pathway). The slow modulation has been proposed\\u000a to arise from the recently described

Daniel Yakubovich; Ida Rishal; Nathan Dascal

2005-01-01

159

AQP1 Is Not Only a Water Channel: It Contributes to Cell Migration through Lin7\\/Beta-Catenin  

Microsoft Academic Search

Background: AQP1 belongs to aquaporins family, water-specific, membrane-channel proteins expressed in diverse tissues. Recent papers showed that during angiogenesis, AQP1 is expressed preferentially by microvessels, favoring angiogenesis via the increase of permeability In particular, in AQP1 null mice, endothelial cell migration is impaired without altering their proliferation or adhesion. Therefore, AQP1 has been proposed as a novel promoter of tumor

Elena Monzani; Riccardo Bazzotti; Carla Perego; Caterina A. M. La Porta

2009-01-01

160

Structure, function and translational relevance of aquaporin dual water and ion channels  

PubMed Central

Aquaporins have been assumed to be selective for water alone, and aquaglyceroporins are accepted as carrying water and small uncharged solutes including glycerol. This review presents an expanded view of aquaporins as channels with more complex mechanisms of regulation and diverse repertoires of substrate permeabilities than were originally appreciated in the early establishment of the field. The role of aquaporins as dual water and gated ion channels is likely to have physiological and potentially translational relevance, and can be evaluated with newly developed molecular and pharmacological tools. Ion channel activity has been shown for Aquaporins -0, -1, and -6, Drosphila Big Brain, and plant Nodulin-26. Although the concept of ion channel function in aquaporins remains controversial, research advances are beginning to define not only the ion channel function but also the detailed molecular mechanisms that govern and mediate the multifunctional capabilities. With regard to physiological relevance, the adaptive benefit of expression of ion channel activity in aquaporins, implied by amino acid sequence conservation of the ion channel gating domains, suggests they provide more than water or glycerol and solute transport. Dual ion and water channels are of interest for understanding the modulation of transmembrane fluid gradients, volume regulation, and possible signal transduction in tissues expressing classes of aquaporins that have the dual function capability. Other aquaporin classes might be found in future work to have ion channel activities, pending identification of the possible signaling pathways that could govern activation.

Yool, Andrea J; Campbell, Ewan M

2012-01-01

161

A versatile flow channel for laboratory experiments with running water macroinvertebrates  

Microsoft Academic Search

Experiments with running water organisms should be conducted under running water conditions. A flow channel which has proved\\u000a useful for long-term rearing of running water macroinvertebrates is described. Through its arena-shaped design and water jet\\u000a drive, damage to drifting animals is practically excluded.

Andreas Frutiger

1984-01-01

162

Three-channel solar radiometer for the determination of atmospheric columnar water vapor.  

PubMed

The design of a three-channel solar radiometer used to determine total columnar atmospheric water-vapor amounts is presented. The main channel is located in the 0.94-µm water-vapor band, and two other channels are located in adjacent nonabsorption regions of the solar spectrum and are used to remove scattering effects from the main channel. Water-vapor transmittance is determined by means of a modified Langley approach, and these transmittances are converted to columnar water vapor by means of a band model developed at the University of Arizona. Several cases are presented in which columnar water-vapor amounts are determined through the use of the instrument and method described here. These results are compared with sounding-balloon results. Tests of the method indicate that columnar water vapor may be retrieved with an uncertainty of less than 10%. PMID:20935984

Thome, K J; Smith, M W; Palmer, J M; Reagan, J A

1994-08-20

163

Distinct Acyl Protein Transferases and Thioesterases Control Surface Expression of Calcium-activated Potassium Channels*  

PubMed Central

Protein palmitoylation is rapidly emerging as an important determinant in the regulation of ion channels, including large conductance calcium-activated potassium (BK) channels. However, the enzymes that control channel palmitoylation are largely unknown. Indeed, although palmitoylation is the only reversible lipid modification of proteins, acyl thioesterases that control ion channel depalmitoylation have not been identified. Here, we demonstrate that palmitoylation of the intracellular S0–S1 loop of BK channels is controlled by two of the 23 mammalian palmitoyl-transferases, zDHHC22 and zDHHC23. Palmitoylation by these acyl transferases is essential for efficient cell surface expression of BK channels. In contrast, depalmitoylation is controlled by the cytosolic thioesterase APT1 (LYPLA1), but not APT2 (LYPLA2). In addition, we identify a splice variant of LYPLAL1, a homolog with ?30% identity to APT1, that also controls BK channel depalmitoylation. Thus, both palmitoyl acyltransferases and acyl thioesterases display discrete substrate specificity for BK channels. Because depalmitoylated BK channels are retarded in the trans-Golgi network, reversible protein palmitoylation provides a critical checkpoint to regulate exit from the trans-Golgi network and thus control BK channel cell surface expression.

Tian, Lijun; McClafferty, Heather; Knaus, Hans-Guenther; Ruth, Peter; Shipston, Michael J.

2012-01-01

164

Aquaporin3 is a sperm water channel essential for postcopulatory sperm osmoadaptation and migration  

PubMed Central

In the journey from the male to female reproductive tract, mammalian sperm experience a natural osmotic decrease (e.g., in mouse, from ?415 mOsm in the cauda epididymis to ?310 mOsm in the uterine cavity). Sperm have evolved to utilize this hypotonic exposure for motility activation, meanwhile efficiently silence the negative impact of hypotonic cell swelling. Previous physiological and pharmacological studies have shown that ion channel-controlled water influx/efflux is actively involved in the process of sperm volume regulation; however, no specific sperm proteins have been found responsible for this rapid osmoadaptation. Here, we report that aquaporin3 (AQP3) is a sperm water channel in mice and humans. Aqp3-deficient sperm show normal motility activation in response to hypotonicity but display increased vulnerability to hypotonic cell swelling, characterized by increased tail bending after entering uterus. The sperm defect is a result of impaired sperm volume regulation and progressive cell swelling in response to physiological hypotonic stress during male-female reproductive tract transition. Time-lapse imaging revealed that the cell volume expansion begins at cytoplasmic droplet, forcing the tail to angulate and form a hairpin-like structure due to mechanical membrane stretch. The tail deformation hampered sperm migration into oviduct, resulting in impaired fertilization and reduced male fertility. These data suggest AQP3 as an essential membrane pathway for sperm regulatory volume decrease (RVD) that balances the “trade-off” between sperm motility and cell swelling upon physiological hypotonicity, thereby optimizing postcopulatory sperm behavior.

Chen, Qi; Peng, Hongying; Lei, Li; Zhang, Ying; Kuang, Haibin; Cao, Yujing; Shi, Qi-xian; Ma, Tonghui; Duan, Enkui

2011-01-01

165

Regulation of the Escherichia coli water channel gene aqpZ  

PubMed Central

Osmotic movement of water across bacterial cell membranes is postulated to be a homeostatic mechanism for maintaining cell turgor. The molecular water transporter remained elusive until discovery of the Escherichia coli water channel, AqpZ, however the regulation of the aqpZ gene expression and physiological function of the AqpZ protein are unknown. Northern analysis revealed a transcript of 0.7 kb, confirming the monocistronic nature of aqpZ. Regulatory studies performed with an aqpZ?lacZ low copy plasmid demonstrate enhanced expression during mid-logarithmic growth, and expression of the gene is dependent upon the extracellular osmolality, which increased in hypoosmotic environments but strongly reduced in hyperosmolar NaCl or KCl. While disruption of the chromosomal aqpZ is not lethal for E. coli, the colonies of the aqpZ knockout mutant are smaller than those of the parental wild-type strain. When cocultured with parental wild-type E. coli, the aqpZ knockout mutant exhibits markedly reduced colony formation when grown at 39°C. Similarly, the aqpZ knockout mutant also exhibits greatly reduced colony formation when grown at low osmolality, but this phenotype is reversed by overexpression of AqpZ protein. These results implicate AqpZ as a participant in the adaptive response of E. coli to hypoosmotic environments and indicate a requirement for AqpZ by rapidly growing cells.

Calamita, Giuseppe; Kempf, Bettina; Bonhivers, Melanie; Bishai, William R.; Bremer, Erhard; Agre, Peter

1998-01-01

166

Transmittance and water retrievals from the B2 channel of the Stratospheric And Mesospheric Sounder  

Microsoft Academic Search

The data from the B2 water vapor channel of the SAMS has been analyzed using a two-stage retrieval process which produces an estimate of transmittance of water for the channel in addition to H2O volume mixing ratio cross sections. The water retrievals range from 70 N to 50 S in latitude and from 4.0 to 9.5 scale heights in the

R. Munro; C. D. Rodgers

1993-01-01

167

The effect of water on protein dynamics.  

PubMed Central

Neutron diffraction and spectroscopy were applied to describe the hydration and dynamics of a soluble protein and a natural membrane from extreme halophilic Archaea. The quantitative dependence of protein motions on water activity was clearly illustrated, and it was established that a minimum hydration shell is required for the systems to access their functional resilience, i.e. a dynamics state that allows biological activity.

Zaccai, G

2004-01-01

168

Mechanism of inhibition of cyclic nucleotide-gated channel by protein tyrosine kinase probed with genistein.  

PubMed

Rod cyclic nucleotide-gated (CNG) channels are modulated by changes in tyrosine phosphorylation catalyzed by protein tyrosine kinases (PTKs) and phosphatases (PTPs). We used genistein, a PTK inhibitor, to probe the interaction between the channel and PTKs. Previously, we found that in addition to inhibiting tyrosine phosphorylation of the rod CNG channel alpha-subunit (RETalpha), genistein triggers a noncatalytic inhibitory interaction between the PTK and the channel. These studies suggest that PTKs affects RETalpha channels in two ways: (1) by catalyzing phosphorylation of the channel protein, and (2) by allosterically regulating channel activation. Here, we study the mechanism of noncatalytic inhibition. We find that noncatalytic inhibition follows the same activity dependence pattern as catalytic modulation (phosphorylation): the efficacy and apparent affinity of genistein inhibition are much higher for closed than for fully activated channels. Association rates with the genistein-PTK complex were similar for closed and fully activated channels and independent of genistein concentration. Dissociation rates were 100 times slower for closed channels, which is consistent with a much higher affinity for genistein-PTK. Genistein-PTK affects channel gating, but not single channel conductance or the number of active channels. By analyzing single channel gating during genistein-PTK dissociation, we determined the maximal open probability for normal and genistein-PTK-bound channels. genistein-PTK decreases open probability by increasing the free energy required for opening, making opening dramatically less favorable. Ni(2+), which potentiates RETalpha channel gating, partially relieves genistein inhibition, possibly by disrupting the association between the genistein-PTK and the channel. Studies on chimeric channels containing portions of RETalpha, which exhibits genistein inhibition, and the rat olfactory CNG channel alpha-subunit, which does not, reveals that a domain containing S6 and flanking regions is the crucial for genistein inhibition and may constitute the genistein-PTK binding site. Thus, genistein-PTK stabilizes the closed state of the channel by interacting with portions of the channel that participate in gating. PMID:11222626

Molokanova, E; Kramer, R H

2001-03-01

169

Independently gated multiple substates of an epithelial chloride-channel protein.  

PubMed Central

We have purified a protein from Necturus maculosus gallbladder cells that forms chloride channels in an artificial membrane. The same protein apparently can form channels that are highly selective for chloride but can have conductances varying from 9 to about 150 pS. The high-conductance channels are blocked by the monoclonal antibody used to purify the protein, but this antibody has no effect on the 9-pS channels. The observation that gating of the low- and high-conductance states is independent and that the antibody affects only the latter has implications regarding the control of chloride conductance in cell membranes and the different types of channels described in those cells. Images Fig. 1

Finn, A L; Dillard, M; Gaido, M

1993-01-01

170

Phycodnavirus potassium ion channel proteins question the virus molecular piracy hypothesis.  

PubMed

Phycodnaviruses are large dsDNA, algal-infecting viruses that encode many genes with homologs in prokaryotes and eukaryotes. Among the viral gene products are the smallest proteins known to form functional K(+) channels. To determine if these viral K(+) channels are the product of molecular piracy from their hosts, we compared the sequences of the K(+) channel pore modules from seven phycodnaviruses to the K(+) channels from Chlorella variabilis and Ectocarpus siliculosus, whose genomes have recently been sequenced. C. variabilis is the host for two of the viruses PBCV-1 and NY-2A and E. siliculosus is the host for the virus EsV-1. Systematic phylogenetic analyses consistently indicate that the viral K(+) channels are not related to any lineage of the host channel homologs and that they are more closely related to each other than to their host homologs. A consensus sequence of the viral channels resembles a protein of unknown function from a proteobacterium. However, the bacterial protein lacks the consensus motif of all K(+) channels and it does not form a functional channel in yeast, suggesting that the viral channels did not come from a proteobacterium. Collectively, our results indicate that the viruses did not acquire their K(+) channel-encoding genes from their current algal hosts by gene transfer; thus alternative explanations are required. One possibility is that the viral genes arose from ancient organisms, which served as their hosts before the viruses developed their current host specificity. Alternatively the viral proteins could be the origin of K(+) channels in algae and perhaps even all cellular organisms. PMID:22685610

Hamacher, Kay; Greiner, Timo; Ogata, Hiroyuki; Van Etten, James L; Gebhardt, Manuela; Villarreal, Luis P; Cosentino, Cristian; Moroni, Anna; Thiel, Gerhard

2012-06-07

171

Phycodnavirus Potassium Ion Channel Proteins Question the Virus Molecular Piracy Hypothesis  

PubMed Central

Phycodnaviruses are large dsDNA, algal-infecting viruses that encode many genes with homologs in prokaryotes and eukaryotes. Among the viral gene products are the smallest proteins known to form functional K+ channels. To determine if these viral K+ channels are the product of molecular piracy from their hosts, we compared the sequences of the K+ channel pore modules from seven phycodnaviruses to the K+ channels from Chlorella variabilis and Ectocarpus siliculosus, whose genomes have recently been sequenced. C. variabilis is the host for two of the viruses PBCV-1 and NY-2A and E. siliculosus is the host for the virus EsV-1. Systematic phylogenetic analyses consistently indicate that the viral K+ channels are not related to any lineage of the host channel homologs and that they are more closely related to each other than to their host homologs. A consensus sequence of the viral channels resembles a protein of unknown function from a proteobacterium. However, the bacterial protein lacks the consensus motif of all K+ channels and it does not form a functional channel in yeast, suggesting that the viral channels did not come from a proteobacterium. Collectively, our results indicate that the viruses did not acquire their K+ channel-encoding genes from their current algal hosts by gene transfer; thus alternative explanations are required. One possibility is that the viral genes arose from ancient organisms, which served as their hosts before the viruses developed their current host specificity. Alternatively the viral proteins could be the origin of K+ channels in algae and perhaps even all cellular organisms.

Hamacher, Kay; Greiner, Timo; Ogata, Hiroyuki; Van Etten, James L.; Gebhardt, Manuela; Villarreal, Luis P.; Cosentino, Cristian; Moroni, Anna; Thiel, Gerhard

2012-01-01

172

Differential Phosphoinositide Binding to Components of the G Protein-Gated K + Channel  

Microsoft Academic Search

The regulation of ion channels and transporters by anionic phospholipids is currently very topical. G protein-gated K+ channels from the Kir3.0 family are involved in slowing the heart rate, generating late inhibitory postsynaptic potentials\\u000a and controlling hormone release from neuroendocrine cells. There is considerable functional precedent for the control of these\\u000a channels by phosphatidylinositol 4,5-bisphosphate. In this study, we used

Alison M. Thomas; Sean G. Brown; Joanne L. Leaney; Andrew Tinker

2006-01-01

173

Primary structure and functional expression of a rat G-protein-coupled muscarinic potassium channel  

Microsoft Academic Search

PARASYMPATHETIC nerve stimulation causes slowing of the heart rate by activation of muscarinic receptors and the subsequent opening of muscarinic K+ channels in the sinoatrial node and atrium1-4. This inwardly rectifying K+ channel is coupled directly with G protein5-10. Based on sequence homology with cloned inwardly rectifying K+ channels, ROMK1 (ref. 11) and IRK1 (ref. 12), we have isolated a

Yoshihiro Kubo; Eitan Reuveny; Paul A. Slesinger; Yuh Nung Jan; Lily Y. Jan

1993-01-01

174

Voltage Gated Sodium Channel Associated Proteins and Alternative Mechanisms of Inactivation and Block  

PubMed Central

Voltage-gated sodium channels mediate inward current of action potentials upon membrane depolarization of excitable cells. The initial transient sodium current is restricted to milliseconds through three distinct channel inactivating and blocking mechanisms. All pore-forming alpha subunits of sodium channels possess structural elements mediating fast inactivation upon depolarization and recovery within milliseconds upon membrane repolarization. Accessory subunits modulate fast inactivation dynamics, but these proteins can also limit current by contributing distinct inactivation and blocking particles. A-type isoforms of fibroblast growth factor homologous factors (FHFs) bear a particle that induces long-term channel inactivation, while sodium channel subunit Nav?4 employs a blocking particle that rapidly dissociates upon membrane repolarization to generate resurgent current. Despite their different physiological functions, the FHF and Nav?4 particles have similarity in amino acid composition and mechanisms for docking within sodium channels. The three competing channel inactivating and blocking processes functionally interact to regulate a neuron’s intrinsic excitability.

Goldfarb, Mitchell

2011-01-01

175

Punching Holes in Membranes: How Oligomeric Pore-Forming Proteins and Lipids Cooperate to Form Aqueous Channels in Membranes  

NASA Astrophysics Data System (ADS)

Many important biological processes are carried out by a small number of proteins working together as a team to accomplish a specific task. Cooperation between the different proteins is often accomplished through the formation of a supramolecular complex, comprised of either identical or different subunits. Although the formation of protein assemblies is a favored mechanism throughout the cell, it becomes especially important in lipid membranes, as evidenced by the numerous cellular events that are either triggered by or result in the formation of protein complexes in membranes. However, due to the difficulties associated with the study of membrane proteins, the formation of oligomers in lipid membranes is perhaps one of the least understood cellular processes. In this chapter we focus our attention on a subset of membrane complexes — namely, those formed by proteins that are able to pass from a water-soluble to a transmembrane form in order to create a water-filled channel through the lipid membrane. These pore-forming proteins (PFPs) are found in many organisms throughout different kingdoms of life, from bacteria to human. They are often involved in cell death mechanisms through their capacity to break membrane permeability barriers, which can lead to dissipation of the membrane potential as well as introduction or leakage of enzymatic proteins. In fact, a large subset of the PFPs are toxins, and referred to in the literature as pore-forming toxins (PFTs). The association of several monomers into an oligomer is almost always an important aspect of the modus operandi of these proteins. Oligomerization can be useful in several ways: it results in structures large enough to delineate nanometer-size water-filled channels in lipid bilayers, it ensures the presence of large hydrophobic surfaces that can support insertion in the membrane, and it permits cooperative formation and insertion mechanisms.

Fradin, Cécile; Satsoura, Dmitri; Andrews, David W.

176

Trapping a translocating protein within the anthrax toxin channel: implications for the secondary structure of permeating proteins  

PubMed Central

Anthrax toxin consists of three proteins: lethal factor (LF), edema factor (EF), and protective antigen (PA). This last forms a heptameric channel, (PA63)7, in the host cell’s endosomal membrane, allowing the former two (which are enzymes) to be translocated into the cytosol. (PA63)7 incorporated into planar bilayer membranes forms a channel that translocates LF and EF, with the N terminus leading the way. The channel is mushroom-shaped with a cap containing the binding sites for EF and LF, and an ?100 Å–long, 15 Å–wide stem. For proteins to pass through the stem they clearly must unfold, but is secondary structure preserved? To answer this question, we developed a method of trapping the polypeptide chain of a translocating protein within the channel and determined the minimum number of residues that could traverse it. We attached a biotin to the N terminus of LFN (the 263-residue N-terminal portion of LF) and a molecular stopper elsewhere. If the distance from the N terminus to the stopper was long enough to traverse the channel, streptavidin added to the trans side bound the N-terminal biotin, trapping the protein within the channel; if this distance was not long enough, streptavidin did not bind the N-terminal biotin and the protein was not trapped. The trapping rate was dependent on the driving force (voltage), the length of time it was applied, and the number of residues between the N terminus and the stopper. By varying the position of the stopper, we determined the minimum number of residues required to span the channel. We conclude that LFN adopts an extended-chain configuration as it translocates; i.e., the channel unfolds the secondary structure of the protein. We also show that the channel not only can translocate LFN in the normal direction but also can, at least partially, translocate LFN in the opposite direction.

Jennings-Antipov, Laura D.; Jakes, Karen S.; Finkelstein, Alan

2011-01-01

177

Aquaporin water channels in the canine gubernaculum testis.  

PubMed

The jelly-like gubernaculum testis (GT) is a hydrated structure consisting of a concentric sheath of dense connective tissue around a loose mesenchymal core, with two cords of skeletal muscle cells asymmetrically placed alongside. Expansion of the GT occurs during the transabdominal phase of testicular descent, linked to cell proliferation together with modifications of the hydric content of the organ. The aim of this study was to detect immunohistochemically the presence of aquaporins (AQPs), integral membrane proteins permitting passive transcellular water movement, in the canine GTs. Samples (n=15) were obtained from pregnancies of 9 medium sized bitches and dissected from healthy fetuses. Five fetuses were aged 35-45 days of gestation, 10 fetuses from 46 days of gestation to delivery, thus offering us the opportunity to study the progressive maturation of the gubernacula. The presence of AQP3, 4, 7, 8 and -9 was assessed in the muscular components of the GT, some of them (AQP3, AQP4, AQP7) with increasing intensity through the second half of pregnancy up to term. AQP1 was localized in the capillary and venous endothelia in the younger fetuses, also in the artery adventitia and in the nerve perineurium in progressively older fetuses. These data demonstrate the potential importance and contribution of AQP-mediated water flux in hydration and volume modification of the growing GT in a canine model. PMID:23305875

Arrighi, Silvana; Aralla, Marina; Fracassetti, Paola; Mobasheri, Ali; Cremonesi, Fausto

2013-01-08

178

33 CFR 207.640 - Sacramento Deep Water Ship Channel Barge Lock and Approach Canals; use, administration, and...  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Sacramento Deep Water Ship Channel Barge Lock...NAVIGATION REGULATIONS § 207.640 Sacramento Deep Water Ship Channel Barge Lock...administration, and navigation. (a) Sacramento Deep Water Ship Channel Barge...

2010-07-01

179

33 CFR 207.640 - Sacramento Deep Water Ship Channel Barge Lock and Approach Canals; use, administration, and...  

Code of Federal Regulations, 2010 CFR

...2009-07-01 2009-07-01 false Sacramento Deep Water Ship Channel Barge Lock...NAVIGATION REGULATIONS § 207.640 Sacramento Deep Water Ship Channel Barge Lock...administration, and navigation. (a) Sacramento Deep Water Ship Channel Barge...

2009-07-01

180

Aquaporin-4 water channels and synaptic plasticity in the hippocampus.  

PubMed

Aquaporin-4 (AQP4) is the major water channel expressed in the central nervous system (CNS) and is primarily expressed in glial cells. Many studies have shown that AQP4 regulates the response of the CNS to insults or injury, but far less is known about the potential for AQP4 to influence synaptic plasticity or behavior. Recent studies have examined long-term potentiation (LTP), long-term depression (LTD), and behavior in AQP4 knockout (KO) and wild-type mice to gain more insight into its potential role. The results showed a selective effect of AQP4 deletion on LTP of the Schaffer collateral pathway in hippocampus using an LTP induction protocol that simulates pyramidal cell firing during theta oscillations (theta-burst stimulation; TBS). However, LTP produced by a different induction protocol was unaffected. There was also a defect in LTD after low frequency stimulation (LFS) in AQP4 KO mice. Interestingly, some slices from AQP4 KO mice exhibited LTD after TBS instead of LTP, or LTP following LFS instead of LTD. These data suggest that AQP4 and astrocytes influence the polarity of long-term synaptic plasticity (potentiation or depression). These potentially powerful roles expand the influence of AQP4 and astrocytes beyond the original suggestions related to regulation of extracellular potassium and water balance. Remarkably, AQP4 KO mice did not show deficits in basal transmission, suggesting specificity for long-term synaptic plasticity. The mechanism appears to be related to neurotrophins and specifically brain-derived neurotrophic factor (BDNF) because pharmacological blockade of neurotrophin trk receptors or scavenging ligands such as BDNF restored plasticity. The in vitro studies predicted effects in vivo of AQP4 deletion because AQP4 KO mice performed worse using a task that requires memory for the location of objects (object placement). However, performance on other hippocampal-dependent tasks was spared. The results suggest an unanticipated and selective role of AQP4 in synaptic plasticity and spatial memory, and underscore the growing appreciation of the role of glial cells in functions typically attributed to neurons. Implications for epilepsy are discussed because of the previous evidence that AQP4 influences seizures, and the role of synaptic plasticity in epileptogenesis. PMID:23684954

Scharfman, Helen E; Binder, Devin K

2013-05-15

181

Effects of Protein, Amino Acid Levels, and Feeding Methods on Growth of Fingerling Channel Catfish.  

National Technical Information Service (NTIS)

Survival of fingerling channel catfish was nearly identical for fish on diets containing 25 percent protein and 22 percent protein. Average gain per fish, gain per pond, and feed conversion were improved when fish received diets with 25 percent protein. L...

C. W. Deyoe O. W. Tiemeier C. Suppes

1968-01-01

182

Immunolocalization of water channel aquaporins in human knee articular cartilage with intact and early degenerative regions.  

PubMed

Aquaporins (AQPs), a family of water channel proteins expressed in various cells and tissues, serve as physiological pathways of water and small solute transport. Articular cartilage is avascular tissue with unique biomechanical structure, a major component of which is "water". Our objective is to investigate the immunolocalization and expression pattern changes of AQPs in articular cartilage with normal and early degenerative regions in the human knee joint, which is the joint most commonly involved in osteoarthritis (OA). Two isoforms (AQPs 1 and 3) of AQPs were examined by immunohistochemical analyses using isoform-specific antibodies with cartilage samples from OA patients undergoing total knee arthroplasty. AQP 1 and AQP 3 were expressed in human knee articular cartilage and were localized in chondrocytes, both in the intact and early degenerative cartilage regions. Compared to the intact cartilage, both AQP 1 and AQP 3 immunopositive cells were observed at the damaged surface area in the degenerative region. These findings suggest that these AQPs play roles in metabolic water regulation in articular cartilage of load bearing joints and that they are responsible for OA onset. PMID:23345027

Hagiwara, Keiichi; Shinozaki, Tetsuya; Matsuzaki, Toshiyuki; Takata, Kuniaki; Takagishi, Kenji

2013-01-24

183

Direct Activation of Mammalian Atrial Muscarinic Potassium Channels by GTP Regulatory Protein Gk  

Microsoft Academic Search

The mammalian heart rate is regulated by the vagus nerve, which acts via muscarinic acetylcholine receptors to cause hyperpolarization of atrial pacemaker cells. The hyperpolarization is produced by the opening of potassium channels and involves an intermediary guanosine triphosphate-binding regulatory (G) protein. Potassium channels in isolated, inside-out patches of membranes from atrial cells now are shown to be activated by

Atsuko Yatani; Juan Codina; Arthur M. Brown; Lutz Birnbaumer

1987-01-01

184

Inhibition by cocaine of G protein-activated inwardly rectifying K + channels expressed in Xenopus oocytes  

Microsoft Academic Search

Cocaine, a commonly abused psychostimulant, interacts with not only transporters for dopamine, serotonin and norepinephrine but also several receptors and channels. However, the molecular mechanisms underlying the various effects of cocaine remain to be clarified. Using the Xenopus oocyte expression assay, we investigated the effects of cocaine on G protein-activated inwardly rectifying K+ (GIRK) channels, which regulate neuronal excitability and

Toru Kobayashi; Daisuke Nishizawa; Tatsunori Iwamura; Kazutaka Ikeda

2007-01-01

185

G-protein-coupled inwardly rectifying potassium channels are targets of alcohol action  

Microsoft Academic Search

G-protein-coupled inwardly rectifying potassium channels (GIRKs) are important for regulation of synaptic transmission and neuronal firing rates. Because of their key role in brain function, we asked if these potassium channels are targets of alcohol action. Ethanol enhanced function of cerebellar granule cell GIRKs coupled to GABAB receptors. Enhancement of GIRK function by ethanol was studied in detail using Xenopus

Walter R. Wilson; R. Dayne Mayfield; Susan J. Brozowski; Richard A. Morrisett; R. Adron Harris; Joanne M. Lewohl

1999-01-01

186

Interactions of cyclic nucleotide-gated channel subunits and protein tyrosine kinase probed with genistein.  

PubMed

The cGMP sensitivity of cyclic nucleotide-gated (CNG) channels can be modulated by changes in phosphorylation catalyzed by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases. Previously, we used genistein, a PTK inhibitor, to probe the interaction between PTKs and homomeric channels comprised of alpha subunits (RETalpha) of rod photoreceptor CNG channels expressed in Xenopus oocytes. We showed that in addition to inhibiting phosphorylation, genistein triggers a noncatalytic interaction between PTKs and homomeric RETalpha channels that allosterically inhibits channel gating. Here, we show that native CNG channels from rods, cones, and olfactory receptor neurons also exhibit noncatalytic inhibition induced by genistein, suggesting that in each of these sensory cells, CNG channels are part of a regulatory complex that contains PTKs. Native CNG channels are heteromers, containing beta as well as alpha subunits. To determine the contributions of alpha and beta subunits to genistein inhibition, we compared the effect of genistein on native, homomeric (RETalpha and OLFalpha), and heteromeric (RETalpha+beta, OLFalpha+beta, and OLFalpha+RETbeta) CNG channels. We found that genistein only inhibits channels that contain either the RETalpha or the OLFbeta subunits. This finding, along with other observations about the maximal effect of genistein and the Hill coefficient of genistein inhibition, suggests that the RETalpha and OLFbeta subunits contain binding sites for the PTK, whereas RETbeta and OLFalpha subunits do not. PMID:10828243

Molokanova, E; Savchenko, A; Kramer, R H

2000-06-01

187

Particularities of the dynamics of river channel processes in the Khabarovsk water junction  

Microsoft Academic Search

The dynamics of river channel processes were analyzed in the region of complex floodplain-channel branching of the Amur River\\u000a near Khabarovsk using remote sensing data of the Earth’s surface. Zones of steady accumulation and long-term erosion of the\\u000a river channel are established within the Khabarovsk water junction over the period of 1964–2004. The main problems related\\u000a to restoring the Amur

V. I. Sinyukov; V. A. Glukhov; O. V. Rybas; A. N. Makhinov; V. I. Kim; N. V. Berdnikov

2008-01-01

188

Groundwater-surface water ecotones at the upstream part of confluences in former river channels  

Microsoft Academic Search

Two slow flowing former channels of the Rhône River, which are supplied by nutrient-poor groundwater and subject to backflows of nutrient-rich water from the Rhone, were studied in order to demonstrate the occurrence of an ecotone located upstream to their confluences with the main channel. In one of the channels, the long-term stability of the boundary zone compared to the

Gudrun Bornettel; Andrew R. G. Large

1995-01-01

189

On the circulation of bottom water in the region of the Vema Channel  

NASA Astrophysics Data System (ADS)

The circulation and transport of Antarctic Bottom Water ( ?4<45.87) in the region of the Vema Channel are studied along three WOCE hydrographic lines, the geostrophic velocities referenced to previously published direct current measurements. The primary supply of water to the deep Vema Channel is from the Argentine Basin's deep western boundary current, with no indication of an inflow from the southeast. In the northern Argentine Basin, detachment of lower North Atlantic Deep Water from the continental slope is associated with a deep thermohaline front near 34°S. To the north of this front, the upper part of the AABW bound for the Vema Channel ( ?4<46.01) exhibits a significant NADW influence. Further modification of the throughflow water occurs near 30°30'S, where the channel orientation changes by ˜50°. Southward flow of bottom water on the eastern flank of the Vema Channel, amounting to ˜1.5 Sv, represents a significant countercurrent to the deep channel transport. Inclusion of this countercurrent reduces the net flow of AABW through the Vema Channel from 3.2±0.7 to 1.7±1.1 Sv. Water properties imply that the near-zero net flow over the Santos Plateau results from a near-closed cyclonic circulation fed by the deep Vema Channel throughflow. A disruption of the northward boundary current in the upper AABW (lower circumpolar water) is required by this flow pattern. The extension of the cyclonic circulation on the Santos Plateau enters the Brazil Basin as a ˜1 Sv flow distinct from the outflow in the Vema Channel Extension (6.2 Sv). The high magnitude of the latter suggests a southward recirculation of bottom water near the western boundary to the north of the region of study.

McDonagh, Elaine L.; Arhan, Michel; Heywood, Karen J.

2002-07-01

190

Structure and chromosomal localization of a human water channel (AQP3) gene  

SciTech Connect

A cDNA encoding rat AQP3, a water channel and a member of the MIP family, that is expressed predominantly in kidney medulla and colon was cloned recently. To determine the structure, tissue distribution, and chromosomal localization of the human AQP3 gene, the authors screened a human kidney cDNA library with rat AQP3 probe and isolated a cDNA coding for human AQP3 protein. The deduced amino acid sequence of human AQP3 was 91% identical to rat AQP3. Human AQP3 mRNA was expressed in colon, kidney, liver, pancreas, lung, peripheral leukocytes, spleen, and prostate. The human AQP3 gene was mapped to 7q36.2-q36.3 by chromosome fluorescence in situ hybridization. 10 refs., 3 figs.

Ishibashi, Kenichi; Sasaki, Sei; Saito, Fumiko [Tokyo Medical and Dental Univ. (Japan)] [and others

1995-05-20

191

Distribution of mRNA encoding the FA-CHIP water channel in amphibian tissues: effects of salt adaptation.  

PubMed

A water channel, the frog aquaporin-CHIP (FA-CHIP) was recently cloned from Rana esculenta urinary bladder. The 28.9 kDa encoded protein shows 78.8%, 77.4%, 42.4% and 35.6% identity with rat CHIP28, human CHIP28, rat WCH-CD and gamma-TIP, other members of the new transmembrane water channel family (Aquaporin-CHIP). We have now studied membranes from different frog (R. esculenta) organs employing semiquantitative PCR using FA-CHIP specific primers and an internal standard to quantify the PCR products. The FA-CHIP mRNA was abundantly expressed in the frog urinary bladder, skin, lung and gall bladder, while a lower expression was detected in the colon, liver and oviduct. FA-CHIP mRNA was not detected in the frog kidney, erythrocytes and brain but its expression was observed in the toad (Bufo arenarum) urinary bladder and skin, showing that FA-CHIP is probably a general amphibian water channel. Salt acclimation is known to increase the water permeability of frog and toad epithelia. We have now observed that salt acclimation for 1, 3, 4 or 5 days markedly increased skin and urinary bladder FA-CHIP mRNA expression. It is generally accepted that water permeability is controlled in these tissues by the rate of water channel transfer from subapical vesicles (aggrephores) to the apical membrane. Our results indicate that water permeability is also regulated at the level of the FA-CHIP transcription. PMID:7539499

Abrami, L; Capurro, C; Ibarra, C; Parisi, M; Buhler, J M; Ripoche, P

1995-02-01

192

Bioluminescence methodology for the detection of protein-protein interactions within the voltage-gated sodium channel macromolecular complex.  

PubMed

Protein-protein interactions are critical molecular determinants of ion channel function and emerging targets for pharmacological interventions. Yet, current methodologies for the rapid detection of ion channel macromolecular complexes are still lacking. In this study we have adapted a split-luciferase complementation assay (LCA) for detecting the assembly of the voltage-gated Na+ (Nav) channel C-tail and the intracellular fibroblast growth factor 14 (FGF14), a functionally relevant component of the Nav channelosome that controls gating and targeting of Nav channels through direct interaction with the channel C-tail. In the LCA, two complementary N-terminus and C-terminus fragments of the firefly luciferase were fused, respectively, to a chimera of the CD4 transmembrane segment and the C-tail of Nav1.6 channel (CD4-Nav1.6-NLuc) or FGF14 (CLuc-FGF14). Co-expression of CLuc-FGF14 and CD4-Nav1.6-NLuc in live cells led to a robust assembly of the FGF14:Nav1.6 C-tail complex, which was attenuated by introducing single-point mutations at the predicted FGF14:Nav channel interface. To evaluate the dynamic regulation of the FGF14:Nav1.6 C-tail complex by signaling pathways, we investigated the effect of kinase inhibitors on the complex formation. Through a platform of counter screenings, we show that the p38/MAPK inhibitor, PD169316, and the I?B kinase inhibitor, BAY 11-7082, reduce the FGF14:Nav1.6 C-tail complementation, highlighting a potential role of the p38MAPK and the I?B/NF?B pathways in controlling neuronal excitability through protein-protein interactions. We envision the methodology presented here as a new valuable tool to allow functional evaluations of protein-channel complexes toward probe development and drug discovery targeting ion channels implicated in human disorders. PMID:22364545

Shavkunov, Alexander; Panova, Neli; Prasai, Anesh; Veselenak, Ron; Bourne, Nigel; Stoilova-McPhie, Svetla; Laezza, Fernanda

2012-02-24

193

Immunosuppressants Implicate Protein Phosphatase Regulation of K^+ Channels in Guard Cells  

Microsoft Academic Search

The elevation of Ca2+ levels in the cytoplasm inactivates inward-rectifying K^+ channels that play a central role in regulating the apertures of stomatal pores in higher plants. However, the mechanism for the Ca2+-mediated inhibition of K^+-channel function is unknown. Using patch-clamp techniques, we show that cyclophilin-cyclosporin A and FK506-binding protein-FK506 complexes, which are highly specific inhibitors of protein phosphatase 2B

Sheng Luan; Weiwei Li; Frank Rusnak; Sarah M. Assmann; Stuart L. Schreiber

1993-01-01

194

Inhibition of G Protein-Activated Inwardly Rectifying K+ Channels by Ifenprodil  

Microsoft Academic Search

G protein-activated inwardly rectifying K+ channels (GIRK, also known as Kir3) are regulated by various G-protein-coupled receptors. Activation of GIRK channels plays an important role in reducing neuronal excitability in most brain regions and the heart rate. Ifenprodil, which is a clinically used cerebral vasodilator, interacts with several receptors, such as ?1 adrenergic, N-methyl-D-aspartate, serotonin and ? receptors. However, the

Toru Kobayashi; Kazuo Washiyama; Kazutaka Ikeda

2006-01-01

195

Lens cell-to-cel channel protein: II. Conformational change in the presence of calmodulin  

Microsoft Academic Search

Summary Lens fibers are coupled by communicating junctions, clusters of cell-to-cell channels composed of a 28-kD intrinsic membrane protein (MIP26). Evidence suggests that these and other cell-to-cell channels may close as a result of protein conformational change induced by activated calmodulin. To test the validity of this hypothesis, we have measured the intrinsic fluorescence emission and far-ultraviolet circular dichroism of

S. J. Girsch; C. Peracchia

1985-01-01

196

Cellular and Subcellular Immunolocalization of Vasopressin-Regulated Water Channel in Rat Kidney  

Microsoft Academic Search

Vasopressin (antidiuretic hormone) regulates body water balance by controlling water permeability of the renal collecting ducts. The control mechanisms may involve alterations in the number or unit conductance of water channels in the apical plasma membrane of collecting-duct cells. How this occurs is unknown, but indirect evidence exists for the \\

Soren Nielsen; Susan R. Digiovanni; Erik Ilso Christensen; Mark A. Knepper; H. William Harris

1993-01-01

197

Cloning and expression of apical membrane water channel of rat kidney collecting tubule  

Microsoft Academic Search

CONCENTRATING urine is mandatory for most mammals to prevent water loss from the body. Concentrated urine is produced in response to vasopressin by the transepithelial recovery of water from the lumen of the kidney collecting tubule through highly water-permeable membranes1,2. In this nephron segment, vaso-pressin regulates water permeability by endo- and exocytosis of water channels from or to the apical

Kiyohide Fushimi; Shinichi Uchida; Yukichi Harat; Yukio Hirata; Fumiaki Marumo; Sei Sasaki

1993-01-01

198

Structural elements in the Girk1 subunit that potentiate G protein-gated potassium channel activity  

PubMed Central

G protein–gated inwardly rectifying K+ (Girk/KIR3) channels mediate the inhibitory effect of many neurotransmitters on excitable cells. Girk channels are tetramers consisting of various combinations of four mammalian Girk subunits (Girk1 to -4). Although Girk1 is unable to form functional homomeric channels, its presence in cardiac and neuronal channel complexes correlates with robust channel activity. This study sought to better understand the potentiating influence of Girk1, using the GABAB receptor and Girk1/Girk2 heteromer as a model system. Girk1 did not increase the protein levels or alter the trafficking of Girk2-containing channels to the cell surface in transfected cells or hippocampal neurons, indicating that its potentiating influence involves enhancement of channel activity. Structural elements in both the distal carboxyl-terminal domain and channel core were identified as key determinants of robust channel activity. In the distal carboxyl-terminal domain, residue Q404 was identified as a key determinant of receptor-induced channel activity. In the Girk1 core, three unique residues in the pore (P) loop (F137, A142, Y150) were identified as a collective potentiating influence on both receptor-dependent and receptor-independent channel activity, exerting their influence, at least in part, by enhancing mean open time and single-channel conductance. Interestingly, the potentiating influence of the Girk1 P-loop is tempered by residue F162 in the second membrane-spanning domain. Thus, discontinuous and sometime opposing elements in Girk1 underlie the Girk1-dependent potentiation of receptor-dependent and receptor-independent heteromeric channel activity.

Wydeven, Nicole; Young, Daniele; Mirkovic, Kelsey; Wickman, Kevin

2012-01-01

199

Localization of the FA-CHIP water channel in frog urinary bladder.  

PubMed

Like mammalian kidney collecting duct, the water permeability of frog urinary bladder epithelial cells is antidiuretic hormone (ADH)-sensitive. In kidney, this permeability is mediated by water channels named aquaporins. We recently reported the cloning of the frog aquaporin CHIP (FA-CHIP), a water channel from frog urinary bladder. FA-CHIP has 79% identity with rat Aquaporin 1 (AQP1) and only 42% identity with the kidney collecting duct Aquaporin 2 (AQP2). The purpose of this study was to examine the localization of FA-CHIP in frog urinary bladder. We raised antibodies against peptides of 15 to 17 residues, encompassing the N-ter and C-ter regions of FA-CHIP. Anti-FA-CHIP antibodies were used for Western blotting, indirect immunofluorescence microscopy and gold labeling electron microscopy in urinary bladder and other frog tissues. By Western blotting of frog urinary bladder total homogenate, the antibodies recognized a band of 29 kDa and glycosylated forms of the protein between 40 and 70 kDa. No signal was found on membrane preparations from epithelial cell homogenate. FA-CHIP was also found in frog skin, brain, gall bladder, and lung. In immunofluorescence microscopy on urinary bladder sections, FA-CHIP was localized to endothelial cells of blood capillaries and on mesothelial cells of the serosal face. Red blood cells, epithelial and basal cells were unstained. The localization of FA-CHIP in cell plasma membranes was confirmed by gold labeling electron microscopy. In other positive tissues, FA-CHIP was also localized to capillaries. In brain, plasma membranes of epithelial cells were also stained. In conclusion, like its mammalian homologue AQP1, FA-CHIP appears to be localized to constitutively water permeable cells of frog. Therefore, it belongs to the AQP1 family of proteins although unlike AQP1, FA-CHIP is absent from red blood cells and kidney. In frog urinary bladder and skin, FA-CHIP probably plays an important role in water transport across the barriers in series with the ADH-sensitive epithelial cells. PMID:9243182

Abrami, L; Gobin, R; Berthonaud, V; Thanh, H L; Chevalier, J; Ripoche, P; Verbavatz, J M

1997-07-01

200

Coronavirus E protein forms ion channels with functionally and structurally-involved membrane lipids.  

PubMed

Coronavirus (CoV) envelope (E) protein ion channel activity was determined in channels formed in planar lipid bilayers by peptides representing either the transmembrane domain of severe acute respiratory syndrome CoV (SARS-CoV) E protein, or the full-length E protein. Both of them formed a voltage independent ion conductive pore with symmetric ion transport properties. Mutations N15A and V25F located in the transmembrane domain prevented the ion conductivity. E protein derived channels showed no cation preference in non-charged lipid membranes, whereas they behaved as pores with mild cation selectivity in negatively-charged lipid membranes. The ion conductance was also controlled by the lipid composition of the membrane. Lipid charge also regulated the selectivity of a HCoV-229E E protein derived peptide. These results suggested that the lipids are functionally involved in E protein ion channel activity, forming a protein-lipid pore, a novel concept for CoV E protein ion channel entity. PMID:22832120

Verdiá-Báguena, Carmina; Nieto-Torres, Jose L; Alcaraz, Antonio; DeDiego, Marta L; Torres, Jaume; Aguilella, Vicente M; Enjuanes, Luis

2012-07-24

201

Physics of the Atmosphere: Response of the Water Vapor Channel of the Meteosat Satellite.  

National Technical Information Service (NTIS)

An accurate model of the atmospheric transmission function is used to obtain the relationship between the cloudless radiances measured by the 6-7 microns Meteosat radiometer (water vapor channel) and the numerical parameters associated to each point of an...

M. Roulleau M. M. Poc N. Scott A. Chedin

1980-01-01

202

Channel Bow in Boiling Water Reactors - Hot Cell Examination Results and Correlation to Measured Bow  

SciTech Connect

An increase in frequency of fuel channel-control blade interference has been observed in Boiling Water Reactors (BWR) in recent years. Many of the channels leading to interference were found to bow towards the control blade in a manner that was inconsistent with the expected bow due to other effects. The pattern of bow appeared to indicate a new channel bow mechanism that differed from the predominant bow mechanism caused by differential growth due to fast-fluence gradients. In order to investigate this new type of channel bow, coupons from several channels with varying degrees of bow were returned to the GE Vallecitos Nuclear Center (VNC) for Post-Irradiation Examination (PIE). This paper describes the characteristics of channel corrosion and hydrogen pickup observed, and relates the observations to the channel exposure level, control history, and measured channel bow. The channels selected for PIE had exposures in the range of 36-48 GWd/MTU and covered a wide range of measured bow. The coupons were obtained at 4 elevations from opposing channel sides adjacent and away from the control blade. The PIE performed on these coupons included visual examination, metallography, and hydrogen concentration measurements. A new mechanism of control-blade shadow corrosion-induced channel bow was found to correlate with differences in the extent of corrosion and corresponding differences in the hydrogen concentration between opposite sides of the channels. The increased corrosion on the control blade sides was found to be dependent on the level of control early in the life of the channel. The contributions of other potential factors leading to increased channel bow and channel-control blade interference are also discussed in this paper. (authors)

Mahmood, S.T. [Global Nuclear Fuel, GE Vallecitos Nuclear Center, 6705 Vallecitos Road, Sunol, CA 94586 (United States); Lin, Y.P.; Dubecky, M.A. [Global Nuclear Fuel, 3901 Castle Hayne Road, m/c H25, Wilmington, NC 28401 (United States); Edsinger, K. [Electric Power Research Institute, 3420 Hillview Avenue, Palo Alto, CA 94304 (United States); Mader, E.V. [Electric Power Research Institute, 1000 River Walk Dr. no. 340, Idaho Falls, ID 83402 (United States)

2007-07-01

203

Age-dependent axonal expression of potassium channel proteins during development in mouse hippocampus.  

PubMed

The development of the hippocampal network requires neuronal activity, which is shaped by the differential expression and sorting of a variety of potassium channels. Parallel to their maturation, hippocampal neurons undergo a distinct development of their ion channel profile. The age-dependent dimension of ion channel occurrence is of utmost importance as it is interdependently linked to network formation. However, data regarding the exact temporal expression of potassium channels during postnatal hippocampal development are scarce. We therefore studied the expression of several voltage-gated potassium channel proteins during hippocampal development in vivo and in primary cultures, focusing on channels that were sorted to the axonal compartment. The Kv1.1, Kv1.2, Kv1.4, and Kv3.4 proteins showed a considerable temporal variation of axonal localization among neuronal subpopulations. It is possible, therefore, that hippocampal neurons possess cell type-specific mechanisms for channel compartmentalization. Thus, age-dependent axonal sorting of the potassium channel proteins offers a new approach to functionally distinguish classes of hippocampal neurons and may extend our understanding of hippocampal circuitry and memory processing. PMID:20012645

Prüss, Harald; Grosse, Gisela; Brunk, Irene; Veh, Rüdiger W; Ahnert-Hilger, Gudrun

2009-12-12

204

Assembling viral channel forming proteins: Vpu from HIV-1.  

PubMed

Different routes of assembly are probed for the transmembrane domain (TMD) of the bitopic membrane protein Vpu from HIV-1. Vpu is responsible for the amplification of viral release from the host cell. The mode of action includes (i) heteroassembly with host factors and (ii) the formation of homo-oligomers, which are able to conduct ions across the lipid membrane. Two different routes of assembling short sequences of the N terminus, including the TMD of Vpu, Vpu1-32 , and Vpu8-26 , are presented by using a combination of classical molecular dynamics (MD) simulations combined with a docking approach. The rim of alanines (Ala-8, -11, -15, and -19) resembles an interlocking motif for the sequential assembly into a dimer and trimer. Simultaneous assembly results in oligomeric bundles (trimers to pentamers) with either tryptophans (Trp-23) or purely hydrophobic residues facing the center. Bundles, with serines facing the pore (Ser-24), are energetically not the lowest structures. For pentameric bundles with Ser-24 facing the pore, no water column develops during a short 25 ns MD simulation. © 2013 Wiley Periodicals, Inc. Biopolymers 99: 517-529, 2013. PMID:23712488

Li, Li-Hua; Hsu, Hao-Jen; Fischer, Wolfgang B

2013-08-01

205

G protein {beta}{gamma} gating confers volatile anesthetic inhibition to Kir3 channels.  

PubMed

G protein-activated inwardly rectifying potassium (GIRK or Kir3) channels are directly gated by the ?? subunits of G proteins and contribute to inhibitory neurotransmitter signaling pathways. Paradoxically, volatile anesthetics such as halothane inhibit these channels. We find that neuronal Kir3 currents are highly sensitive to inhibition by halothane. Given that Kir3 currents result from increased G?? available to the channels, we asked whether reducing available G?? to the channel would adversely affect halothane inhibition. Remarkably, scavenging G?? using the C-terminal domain of ?-adrenergic receptor kinase (c?ARK) resulted in channel activation by halothane. Consistent with this effect, channel mutants that impair G?? activation were also activated by halothane. A single residue, phenylalanine 192, occupies the putative G?? gate of neuronal Kir3.2 channels. Mutation of Phe-192 at the gate to other residues rendered the channel non-responsive, either activated or inhibited by halothane. These data indicated that halothane predominantly interferes with G??-mediated Kir3 currents, such as those functioning during inhibitory synaptic activity. Our report identifies the molecular correlate for anesthetic inhibition of Kir3 channels and highlights the significance of these effects in modulating neurotransmitter-mediated inhibitory signaling. PMID:21044958

Styer, Amanda M; Mirshahi, Uyenlinh L; Wang, Chuan; Girard, Laura; Jin, Taihao; Logothetis, Diomedes E; Mirshahi, Tooraj

2010-11-02

206

G Protein ?? Gating Confers Volatile Anesthetic Inhibition to Kir3 Channels*  

PubMed Central

G protein-activated inwardly rectifying potassium (GIRK or Kir3) channels are directly gated by the ?? subunits of G proteins and contribute to inhibitory neurotransmitter signaling pathways. Paradoxically, volatile anesthetics such as halothane inhibit these channels. We find that neuronal Kir3 currents are highly sensitive to inhibition by halothane. Given that Kir3 currents result from increased G?? available to the channels, we asked whether reducing available G?? to the channel would adversely affect halothane inhibition. Remarkably, scavenging G?? using the C-terminal domain of ?-adrenergic receptor kinase (c?ARK) resulted in channel activation by halothane. Consistent with this effect, channel mutants that impair G?? activation were also activated by halothane. A single residue, phenylalanine 192, occupies the putative G?? gate of neuronal Kir3.2 channels. Mutation of Phe-192 at the gate to other residues rendered the channel non-responsive, either activated or inhibited by halothane. These data indicated that halothane predominantly interferes with G??-mediated Kir3 currents, such as those functioning during inhibitory synaptic activity. Our report identifies the molecular correlate for anesthetic inhibition of Kir3 channels and highlights the significance of these effects in modulating neurotransmitter-mediated inhibitory signaling.

Styer, Amanda M.; Mirshahi, Uyenlinh L.; Wang, Chuan; Girard, Laura; Jin, Taihao; Logothetis, Diomedes E.; Mirshahi, Tooraj

2010-01-01

207

Optimization of 3D Poisson-Nernst-Planck model for fast evaluation of diverse protein channels.  

PubMed

We show the accuracy and applicability of our fast algorithmic implementation of a three-dimensional Poisson-Nernst-Planck (3D-PNP) flow model for characterizing different protein channels. Due to its high computational efficiency, our model can predict the full current-voltage characteristics of a channel within minutes, based on the experimental 3D structure of the channel or its computational model structure. Compared with other methods, such as Brownian dynamics, which currently needs a few weeks of the computational time, or even much more demanding molecular dynamics modeling, 3D-PNP is the only available method for a function-based evaluation of very numerous tentative structural channel models. Flow model tests of our algorithm and its optimal parametrization are provided for five native channels whose experimental structures are available in the protein data bank (PDB) in an open conductive state, and whose experimental current-voltage characteristics have been published. The channels represent very different geometric and structural properties, which makes it the widest test to date of the accuracy of 3D-PNP on real channels. We test whether the channel conductance, rectification, and charge selectivity obtained from the flow model, could be sufficiently sensitive to single-point mutations, related to unsignificant changes in the channel structure. Our results show that the classical 3D-PNP model, under proper parametrization, is able to achieve a qualitative agreement with experimental data for a majority of the tested characteristics and channels, including channels with narrow and irregular conductivity pores. We propose that although the standard PNP model cannot provide insight into complex physical phenomena due to its intrinsic limitations, its semiquantitative agreement is achievable for rectification and selectivity at a level sufficient for the bioinformatical purpose of selecting the best structural models with a great advantage of a very short computational time. Proteins 2013; 81:1802-1822. © 2013 Wiley Periodicals, Inc. PMID:23720356

Dyrka, Witold; Bartuzel, Maciej M; Kotulska, Malgorzata

2013-08-19

208

Akt regulates L-type Ca2+ channel activity by modulating Cav?1 protein stability  

PubMed Central

The insulin IGF-1–PI3K–Akt signaling pathway has been suggested to improve cardiac inotropism and increase Ca2+ handling through the effects of the protein kinase Akt. However, the underlying molecular mechanisms remain largely unknown. In this study, we provide evidence for an unanticipated regulatory function of Akt controlling L-type Ca2+ channel (LTCC) protein density. The pore-forming channel subunit Cav?1 contains highly conserved PEST sequences (signals for rapid protein degradation), and in-frame deletion of these PEST sequences results in increased Cav?1 protein levels. Our findings show that Akt-dependent phosphorylation of Cav?2, the LTCC chaperone for Cav?1, antagonizes Cav?1 protein degradation by preventing Cav?1 PEST sequence recognition, leading to increased LTCC density and the consequent modulation of Ca2+ channel function. This novel mechanism by which Akt modulates LTCC stability could profoundly influence cardiac myocyte Ca2+ entry, Ca2+ handling, and contractility.

Zhang, Deng-Hong; DeSantiago, Jaime; Aimond, Franck; Barbara, Guillaume; Chemin, Jean; Bonci, Desire; Picht, Eckard; Rusconi, Francesca; Dalton, Nancy D.; Peterson, Kirk L.; Richard, Sylvain; Bers, Donald M.; Brown, Joan Heller; Condorelli, Gianluigi

2009-01-01

209

Pressure-induced water transport in membrane channels studied by molecular dynamics.  

PubMed Central

A method is proposed to measure the water permeability of membrane channels by means of molecular dynamics simulations. By applying a constant force to the bulk water molecules and a counter force on the complementary system, a hydrostatic pressure difference across the membrane can be established, producing a net directional water flow. The hydraulic or osmotic permeability can then be determined by the ratio of the water flux and the pressure difference. The method is applied and tested on an aquaglyceroporin channel through a series of simulations totaling 5 ns in duration.

Zhu, Fangqiang; Tajkhorshid, Emad; Schulten, Klaus

2002-01-01

210

Protein translocation through anthrax toxin channels formed in planar lipid bilayers.  

PubMed

The 63-kDa fragment of the protective antigen (PA) component of anthrax toxin forms a heptameric channel, (PA63)7, in acidic endosomal membranes that leads to the translocation of edema factor (EF) and lethal factor (LF) to the cytosol. It also forms a channel in planar phospholipid bilayer membranes. What role does this channel play in the translocation of EF and LF? We report that after the 263-residue N-terminal piece of LF (LFN) binds to its receptor on the (PA63)7 channel and its N-terminal end enters the channel at small positive voltages to block it, LFN is translocated through the channel to the opposite side at large positive voltages, thereby unblocking it. Thus, all of the translocation machinery is contained in the (PA63)7 channel, and translocation does not require any cellular proteins. The kinetics of this translocation are S-shaped, voltage-dependent, and occur on a timescale of seconds. We suggest that the translocation process might be explained simply by electrophoresis of unfolded LFN through the channel, but the refolding of the N-terminal half of LFN as it emerges from the channel may also provide energy for moving the rest of the molecule through the channel. PMID:15377524

Zhang, Sen; Udho, Eshwar; Wu, Zhengyan; Collier, R John; Finkelstein, Alan

2004-09-17

211

Performance analysis of a LDPC coded OFDM communication system in shallow water acoustic channels  

NASA Astrophysics Data System (ADS)

Time-varying significant multipath interference is the major obstacle to reliable data communication in shallow water acoustic channels. In this paper, the performance of a low density parity check (LDPC) coded orthogonal frequency division multiplexing (OFDM) communication system is investigated for these channels. The initial message for LDPC, decoded by using the belief propagation (BP) algorithm, is deduced for OFDM underwater acoustic channels; based on this deduction, the noise thresholds of regular LDPC codes with different code rates are obtained by using the density evolution algorithm. Furthermore, a communication system model, developed with LDPC code, OFDM and channel interleaver for shallow water acoustic channels, is introduced. The effect of modulation and coding schemes on the LDPC codes performance is investigated by simulation. The results show that the system can achieve remarkable performance in shallow water acoustic channels, and the performance improves with increasing code length and decreasing code rate. The bit error rate (BER) of the system, under conditions with QPSK modulation, 1280-code length and 1/2-code rate, is less than 10-5 when the signal to noise ratio (SNR) is greater than 6.8dB. These values are obtained for a five-path shallow water acoustic channel of Xiamen harbor.

Liu, Shengxing; Xu, Xiaomei

2012-11-01

212

Sizing the Protein Translocation Pathway of Colicin Ia Channels  

PubMed Central

The bacterial toxin colicin Ia forms voltage-gated channels in planar lipid bilayers. The toxin consists of three domains, with the carboxy-terminal domain (C-domain) responsible for channel formation. The C-domain contributes four membrane-spanning segments and a 68-residue translocated segment to the open channel, whereas the upstream domains and the amino-terminal end of the C-domain stay on the cis side of the membrane. The isolated C-domain, lacking the two upstream domains, also forms channels; however, the amino terminus and one of the normally membrane-spanning segments can move across the membrane. (This can be observed as a drop in single-channel conductance.) In longer carboxy-terminal fragments of colicin Ia that include ?169 residues upstream from the C-domain, the entire upstream region is translocated. Presumably, a portion of the C-domain creates a pathway for the polar upstream region to move through the membrane. To determine the size of this translocation pathway, we have attached “molecular stoppers,” small disulfide-bonded polypeptides, to the amino terminus of the C-domain, and determined whether they could be translocated. We have found that the translocation rate is strongly voltage dependent, and that at voltages ?90 mV, even a 26-Å stopper is translocated. Upon reduction of their disulfide bonds, all of the stoppers are easily translocated, indicating that it is the folded structure, rather than some aspect of the primary sequence, that slows translocation of the stoppers. Thus, the pathway for translocation is ?26 Å in diameter, or can stretch to this value. This is large enough for an ?-helical hairpin to fit through.

Kienker, Paul K.; Jakes, Karen S.; Blaustein, Robert O.; Miller, Christopher; Finkelstein, Alan

2003-01-01

213

Heterogeneities in confined water and protein hydration water  

NASA Astrophysics Data System (ADS)

We report recent efforts to understand a broad range of experiments on confined water and protein hydration water, many initiated by a collaboration between workers at the University of Messina and MIT—the editors of this special issue. Preliminary calculations are not inconsistent with one tentative interpretation of these experiments as resulting from the system passing from the high-temperature high-pressure 'HDL' side of the Widom line (where the liquid might display non-Arrhenius behavior) to the low-temperature low-pressure 'LDL' side of the Widom line (where the liquid might display Arrhenius behavior). The Widom line—defined to be the line in the pressure-temperature plane where the correlation length has its maximum—arises if there is a critical point. Hence, interpreting the Messina-MIT experiments in terms of a Widom line is of potential relevance to testing, experimentally, the hypothesis that water displays a liquid-liquid critical point.

Stanley, H. E.; Kumar, P.; Han, S.; Mazza, M. G.; Stokely, K.; Buldyrev, S. V.; Franzese, G.; Mallamace, F.; Xu, L.

2009-12-01

214

Piezo proteins are pore-forming subunits of mechanically activated channels.  

PubMed

Mechanotransduction has an important role in physiology. Biological processes including sensing touch and sound waves require as-yet-unidentified cation channels that detect pressure. Mouse Piezo1 (MmPiezo1) and MmPiezo2 (also called Fam38a and Fam38b, respectively) induce mechanically activated cationic currents in cells; however, it is unknown whether Piezo proteins are pore-forming ion channels or modulate ion channels. Here we show that Drosophila melanogaster Piezo (DmPiezo, also called CG8486) also induces mechanically activated currents in cells, but through channels with remarkably distinct pore properties including sensitivity to the pore blocker ruthenium red and single channel conductances. MmPiezo1 assembles as a ?1.2-million-dalton homo-oligomer, with no evidence of other proteins in this complex. Purified MmPiezo1 reconstituted into asymmetric lipid bilayers and liposomes forms ruthenium-red-sensitive ion channels. These data demonstrate that Piezo proteins are an evolutionarily conserved ion channel family involved in mechanotransduction. PMID:22343900

Coste, Bertrand; Xiao, Bailong; Santos, Jose S; Syeda, Ruhma; Grandl, Jörg; Spencer, Kathryn S; Kim, Sung Eun; Schmidt, Manuela; Mathur, Jayanti; Dubin, Adrienne E; Montal, Mauricio; Patapoutian, Ardem

2012-02-19

215

Control of the Selectivity of the Aquaporin Water Channel Family by Global Orientational Tuning  

NASA Astrophysics Data System (ADS)

Aquaporins are transmembrane channels found in cell membranes of all life forms. We examine their apparently paradoxical property, facilitation of efficient permeation of water while excluding protons, which is of critical importance to preserving the electrochemical potential across the cell membrane. We have determined the structure of the Escherichia coli aquaglyceroporin GlpF with bound water, in native (2.7 angstroms) and in W48F/F200T mutant (2.1 angstroms) forms, and carried out 12-nanosecond molecular dynamics simulations that define the spatial and temporal probability distribution and orientation of a single file of seven to nine water molecules inside the channel. Two conserved asparagines force a central water molecule to serve strictly as a hydrogen bond donor to its neighboring water molecules. Assisted by the electrostatic potential generated by two half-membrane spanning loops, this dictates opposite orientations of water molecules in the two halves of the channel, and thus prevents the formation of a ``proton wire,'' while permitting rapid water diffusion. Both simulations and observations revealed a more regular distribution of channel water and an increased water permeability for the W48F/F200T mutant.

Tajkhorshid, Emad; Nollert, Peter; Jensen, Morten Ø.; Miercke, Larry J. W.; O'Connell, Joseph; Stroud, Robert M.; Schulten, Klaus

2002-04-01

216

Inactivation of Photosystems I and II in Response to Osmotic Stress in Synechococcus. Contribution of Water Channels1  

PubMed Central

The effects of osmotic stress due to sorbitol on the photosynthetic machinery were investigated in the cyanobacterium Synechococcus R-2. Incubation of cells in 1.0 m sorbitol inactivated photosystems I and II and decreased the intracellular solute space by 50%. These effects of sorbitol were reversible: Photosynthetic activity and cytoplasmic volume returned to the original values after removal of the osmotic stress. A blocker of water channels prevented the osmotic-stress-induced inactivation and shrinkage of the intracellular space. It also prevented the recovery of photosynthetic activity and cytoplasmic volume when applied just before release from osmotic stress. Inhibition of protein synthesis by lincomycin had no significant effects on the inactivation and recovery processes, an observation that suggests that protein synthesis was not involved in these processes. Our results suggest that osmotic stress decreased the amount of water in the cytoplasm via the efflux of water through water channels (aquaporins), with resultant increases in intracellular concentrations of ions and a decrease in photosynthetic activity.

Allakhverdiev, Suleyman I.; Sakamoto, Atsushi; Nishiyama, Yoshitaka; Murata, Norio

2000-01-01

217

Identification and characterisation of a functional aquaporin water channel (Anomala cuprea DRIP) in a coleopteran insect.  

PubMed

Water transport across the plasma membrane depends on the presence of the water channel aquaporin (AQP), which mediates the bulk movement of water through osmotic and pressure gradients. In terrestrial insects, which are solid and/or plant feeders, the entrance and exit of water is primarily executed along the alimentary tract, where the hindgut, particularly the rectum, is the major site of water conservation. A cDNA encoding the homologue of the water-specific Drosophila AQP [Drosophila integral protein (DRIP)] was identified through the RT-PCR of RNA isolated from the rectum of the cupreous chafer larvae, Anomala cuprea, a humus and plant root feeder. This gene (Anocu AQP1) has a predicted molecular mass of 26.471 kDa, similar to the DRIP clade of insect AQPs characterised from caterpillars, flies and several liquid-feeding insects. When expressed in Xenopus laevis oocytes, Anocu AQP1 showed the hallmarks of aquaporin-mediated water transport but no glycerol or urea permeability, and the reversible inhibition of elevated water transport through 1 mmol l(-1) HgCl2. This is the first experimental demonstration of the presence of a water-specific AQP, namely DRIP, in the Coleoptera. The genome of the model beetle Tribolium castaneum contains six putative AQP sequences, one of which (Trica-1a, XP_972862) showed the highest similarity to Anocu AQP1 (~60% amino acid identity). Anocu AQP1 is predominantly expressed in the rectum. Using a specific antibody raised against DRIP in the silkworm Bombyx mori (AQP-Bom1), Anocu AQP1 was localised to the apical plasma membrane of rectal epithelial cells, and lacking in the midgut and gastric caecal epithelia. Based on the BeetleBase prediction, there are three putative AQPs (Trica-3a, 3b, 3c: XP_970728, 970912, 970791) that are homologous to B. mori aquaglyceroporin [AQP-Bom2 (GLP)]. The immunocytochemical studies using the specific anti-peptide antibody against AQP-Bom2 revealed the presence of the GLP homologue at the apical plasma membrane of enterocytes in the midgut and gastric caeca. Thus, DRIP (Anocu AQP1) and the putative GLP share epithelial fluid-transporting roles along the alimentary tract in cupreous chafer larvae. PMID:23531819

Nagae, Tomone; Miyake, Seiji; Kosaki, Shiho; Azuma, Masaaki

2013-03-26

218

Water and sediment transport of channel-flat systems in a mesotidal mudflat: Willapa Bay, Washington  

NASA Astrophysics Data System (ADS)

The muddy tidal flats of southern Willapa Bay, Washington are tidally dominated and receive little direct freshwater input. We use data from instruments deployed in channels of different size and on their adjacent flats to investigate the hydrodynamics and sediment dynamics of each morphological setting under a range of seasonal and meteorological conditions, including rain and wind events. Interaction between the morphology of the channel/flat complex and tidal water-level variations produces well-defined velocity pulses during both flooding and ebbing tides. These pulses represent about 27% of the total along-channel water transport and 35% of the suspended-sediment transport of the system. Maintenance of continuity produces the velocity pulse, and pulse magnitude is determined by tidal range. Wind alters the flow regime in channels and on the flat, enhancing over-flat ebb flow in this study location while decreasing ebb-pulse intensity. Wind speed was positively correlated with minimum suspended-sediment concentration. Precipitation falling directly on flats was found to erode flat sediment, which subsequently formed a temporary deposit in the adjacent channel. Residual along-channel water transport in channels and on nearby flats was flood dominant under all seasonal conditions sampled, and sediment flux was flood dominant during winter and spring deployments.

Nowacki, Daniel J.; Ogston, Andrea S.

219

Partitioning of Water Discharge by Distributary Channels in the Prograding, Wax Lake Delta, Coastal Louisiana, USA  

NASA Astrophysics Data System (ADS)

How water and sediment is routed through distributary networks on river deltas is incompletely known and a topic of much active research. We have undertaken a study to determine the controls on partitioning of water and sediment discharge in distributary channels of the Wax Lake Delta and to connect these transport processes to the land building associated with the growth of islands that separate distributary channels from each other. Here we present first results from the field project that defines how water from the upstream primary channel is partitioned between the first set of five distributary channels. Measurements of water discharge and channel bathymetry were collected using a 22-ft research vessel equipped with an acoustic Doppler velocity profiler, a swath bathymetry profiler and dual differential GPS antennas. Wax Lake Delta is situated at the downstream end of Wax Lake Outlet, a man-made channel that diverts water and sediment from the lower Atchafalaya River, roughly 20 km upstream from Morgan City, LA. The subaerial delta has been building out into Atchafalaya Bay since roughly 1973 with a delta-front advance rate of about 0.27 km/yr. Associated with this growth has been development of a distributary network of channels that continues to evolve as the delta progrades seaward. Measurements collected in May, 2007 define properties of the upstream channel and the first set of five distributary channels. Characteristic width, depth and water discharge for the upstream channel are 420 m, 21.2 m, and 2900 m3/s. Characteristic values for width, depth and water discharge for the five distributary channels are 1) 270 m, 6.7 m, and 310 m3/s, 2) 300 m, 6.5 m, and 350 m3/s, 3) 650 m, 6.8 m, and 820 m3/s, 4) 395 m, 6.5 m, and 560 m3/s, and 5) 440 m, 6.0 m, and 440 m3/s. These data highlight a number of interesting points regarding the initial set of bifurcations. First, the transition from one to five channels is associated with a two-thirds reduction in characteristic flow depth and one-third reduction in characteristic flow velocity. Measured discharge in the five channels sums to 86% of the upstream channel. Based on field observations we propose that the remaining 14% is associated with shallow flow onto and across the weakly emergent islands. There is very little difference in characteristic channel depth even though widths of the five channels vary by greater than a factor of two. There is also very little difference in the spatially average velocity for the five channels; velocities range between 0.17-0.22 m/s. All of these channel properties will be discussed in the context of sediment transport and sedimentation within this active delta.

Buttles, J.; Mohrig, D.; Nittrouer, J.; McElroy, B.; Baitis, E.; Allison, M.; Paola, C.; Parker, G.; Kim, W.

2007-12-01

220

Effect of channel catfish stocking rate on yield and water quality in an intensive production system  

Technology Transfer Automated Retrieval System (TEKTRAN)

The effect of stocking rate on production of NWAC 103 strain channel catfish (Ictalurus punctatus) and water quality was investigated using a completely randomized design in an intensively managed biofloc raceway system. Each of the 9 HDPE-lined raceways (4.6 m x 9.2 m with a 0.9-m water depth; 42.2...

221

Control of the Selectivity of the Aquaporin Water Channel Family by Global Orientational Tuning  

Microsoft Academic Search

Aquaporins are transmembrane channels found in cell membranes of all life forms. We examine their apparently paradoxical property, facilitation of efficient permeation of water while excluding protons, which is of critical importance to preserving the electrochemical potential across the cell membrane. We have determined the structure of the Escherichia coli aquaglyceroporin GlpF with bound water, in native (2.7 angstroms) and

Emad Tajkhorshid; Peter Nollert; Morten Ø. Jensen; Larry J. W. Miercke; Joseph O'Connell; Robert M. Stroud; Klaus Schulten

2002-01-01

222

Acute toxicity of waters from the urban drainage channels of Santos (São Paulo, Brazil)  

Microsoft Academic Search

The objective of this study was to evaluate the toxicity of water which flows toward the beaches of Santos, SP, Brazil. Water samples were collected from eight urban drainage channels and a small creek, in March, April and August 2005. For each sample, some physical-chemical parameters were analyzed: pH, dissolved oxygen, temperature, salinity, presence of free chlorine and total ammonia

ANDRÉA PIMENTA AMBROZEVICIUS; DENIS MOLEDO DE SOUZA ABESSA

223

Generation of focused shock waves by multi-channel discharge in water  

Microsoft Academic Search

A new method for generation of focused shock waves in water has been developed where a cylindrical pressure wave is focused by a metallic, parabolic reflector. The pressure wave is created by a high voltage multi-channel discharge in water with an increased electrical conductivity. The discharge is formed on a composite anode consisting of a cylindrical metallic electrode covered by

P. Sunka; V. Babicky; A. Clupek; A. Fuciman; J. Schmidt; J. Benes

2001-01-01

224

Flow cytometry and sorting of amphibian bladder endocytic vesicles containing ADH-sensitive water channels  

Microsoft Academic Search

The water permeability of ADH target epithelial cells is believed to be regulated by a cycle of exo-endocytosis of vesicles containing functional water channels. These vesicles were selectively labeled in intact frog urinary bladders with an impermeant fluorescent marker, 6-carboxyfluorescein. Vesicle suspensions containing the labeled endosomes were obtained by homogenization and differential centrifugation of bladder epithelial cells. The osmotic permeability

F. G. Goot; A. Seigneur; J.-C. Gaucher; P. Ripoche

1992-01-01

225

Outflow Channels and Martian Climate: General Circulation Model (GCM) Simulations with Emplaced Water  

Microsoft Academic Search

The existence of past surface water on Mars has been inferred on the basis of geomorphologic interpretation of spacecraft images. Among the most intriguing signatures of surface water are large outflow channels believed to have been carved out by gigantic flood events in the late Noachian or Hesperian. We use the NASA Ames Mars General Circulation Model (MGCM) to study

D. Santiago; A. Colaprete; R. Haberle; E. Asphaug; L. Sloan

2005-01-01

226

The TMEM16 Protein Family: A New Class of Chloride Channels?  

PubMed Central

Abstract Cl? channels play important roles in many physiological processes, including transepithelial ion absorption and secretion, smooth and skeletal muscle contraction, neuronal excitability, sensory perception, and cell volume regulation. The molecular identity of many types of Cl? channels is still unknown. Recently, three research groups have arrived independently at the identification of TMEM16A (also known as anoctamin-1) as a membrane protein strongly related to the activity of Ca2+-activated Cl? channels (CaCCs). Site-specific mutagenesis of TMEM16A alters the properties of the channels, thus suggesting that TMEM16A forms, at least in part, the CaCC. TMEM16A is a member of a family that includes nine other membrane proteins. All TMEM16 proteins have a similar structure, with eight putative transmembrane domains and cytosolic amino- and carboxy-termini. TMEM16B expression also evokes the appearance of CaCCs, but with biophysical characteristics (voltage dependence, unitary conductance) different from those associated to TMEM16A. The roles of the other TMEM16 proteins are still unknown. The study of TMEM16 proteins may lead to identification of novel molecular mechanisms underlying ion transport and channel gating by voltage and Ca2+.

Galietta, Luis J.V.

2009-01-01

227

33 CFR 207.640 - Sacramento Deep Water Ship Channel Barge Lock and Approach Canals; use, administration, and...  

Code of Federal Regulations, 2013 CFR

33 Navigation and Navigable Waters 3 2013-07-01 2013-07-01 false Sacramento Deep Water Ship Channel Barge Lock and Approach Canals...Section 207.640 Navigation and Navigable Waters CORPS OF ENGINEERS, DEPARTMENT OF...

2013-07-01

228

Emerging concepts for G protein-gated inwardly rectifying potassium (GIRK) channels in health and disease  

PubMed Central

G protein-gated inwardly rectifying potassium (GIRK) channels hyperpolarize neurons in response to the activation of many G-protein coupled receptors and thus control the excitability of neurons through GIRK-mediated self-inhibition, slow synaptic potentials and volume transmission. GIRK channel function and trafficking are highly dependent on their subunit composition. Pharmacological investigations of GIRK channels and studies in animal models suggest that GIRK activity has an important role in physiological responses, including pain perception and memory modulation. Moreover, abnormal GIRK function has been implicated in altering neuronal excitability and cell death that may be important in the pathophysiology of human diseases such as epilepsy, Down’s syndrome, Parkinson’s disease and drug addiction. GIRK channels may therefore prove to be a valuable new therapeutic target for treating these health problems.

Luscher, Christian; Slesinger, Paul A.

2010-01-01

229

Outer membrane protein A of Escherichia coli forms temperature-sensitive channels in planar lipid bilayers.  

PubMed

The temperature dependence of single-channel conductance and open probability for outer membrane protein A (OmpA) of Escherichia coli were examined in planar lipid bilayers. OmpA formed two interconvertible conductance states, small channels, 36-140 pS, between 15 and 37 degrees C, and large channels, 115-373 pS, between 21 and 39 degrees C. Increasing temperatures had strong effects on open probabilities and on the ratio of large to small channels, particularly between 22 and 34 degrees C, which effected sharp increases in average conductance. The data infer that OmpA is a flexible temperature-sensitive protein that exists as a small pore structure at lower temperatures, but refolds into a large pore at higher temperatures. PMID:14644420

Zakharian, E; Reusch, R N

2003-12-01

230

Bioinformatic Characterization of the Trimeric Intracellular Cation-Specific Channel Protein Family  

Microsoft Academic Search

Trimeric intracellular cation-specific (TRIC) channels are integral to muscle excitation–contraction coupling. TRIC channels\\u000a provide counter-ionic flux when calcium is rapidly transported from intracellular stores to the cell cytoplasm. Until recently,\\u000a knowledge of the presence of these proteins was limited to animals. We analyzed the TRIC family and identified a profusion\\u000a of prokaryotic family members with topologies and motifs similar to

Abe L. F. Silverio; Milton H. Saier

2011-01-01

231

IUPHAR-DB: the IUPHAR database of G protein-coupled receptors and ion channels  

Microsoft Academic Search

The IUPHAR database (IUPHAR-DB) integrates peer- reviewed pharmacological, chemical, genetic, func- tional and anatomical information on the 354 non- sensory G protein-coupled receptors (GPCRs), 71 ligand-gated ion channel subunits and 141 voltage- gated-like ion channel subunits encoded by the human, rat and mouse genomes. These genes repre- sent the targets of approximately one-third of cur- rently approved drugs and are

Anthony J. Harmar; Rebecca A. Hills; Edward M. Rosser; Martin Jones; O. Peter Buneman; Donald R. Dunbar; Stuart D. Greenhill; Valerie A. Hale; Joanna L. Sharman; Tom I. Bonner; William A. Catterall; Anthony P. Davenport; Philippe Delagrange; Colin T. Dollery; Steven M. Foord; George A. Gutman; Vincent Laudet; Richard R. Neubig; Eliot H. Ohlstein; Richard W. Olsen; John Peters; Jean-philippe Pin; Robert R. Ruffolo; David B. Searls; Mathew W. Wright; Michael Spedding

2009-01-01

232

TMEM16A, A Membrane Protein Associated with Calcium-Dependent Chloride Channel Activity  

Microsoft Academic Search

Calcium-dependent chloride channels are required for normal electrolyte and fluid secretion, olfactory perception, and neuronal and smooth muscle excitability. The molecular identity of these membrane proteins is still unclear. Treatment of bronchial epithelial cells with interleukin-4 (IL-4) causes increased calcium-dependent chloride channel activity, presumably by regulating expression of the corresponding genes. We performed a global gene expression analysis to identify

Antonella Caputo; Emanuela Caci; Loretta Ferrera; Nicoletta Pedemonte; Cristina Barsanti; Elvira Sondo; Ulrich Pfeffer; Roberto Ravazzolo; Olga Zegarra-Moran; Luis J. V. Galietta

2008-01-01

233

Expression of G-protein inwardly rectifying potassium channels (GIRKs) in lung cancer cell lines  

Microsoft Academic Search

BACKGROUND: Previous data from our laboratory has indicated that there is a functional link between the ?-adrenergic receptor signaling pathway and the G-protein inwardly rectifying potassium channel (GIRK1) in human breast cancer cell lines. We wanted to determine if GIRK channels were expressed in lung cancers and if a similar link exists in lung cancer. METHODS: GIRK1-4 expression and levels

Howard K Plummer III; Madhu S Dhar; Maria Cekanova; Hildegard M Schuller

2005-01-01

234

Modulation of Mitochondrial ATP-Dependent K1 Channels by Protein Kinase C  

Microsoft Academic Search

Pharmacological openers of mitochondrial ATP-dependent K 1 (mitoKATP) channels mimic ischemic precondi- tioning, and such cardioprotection can be prevented by mitoKATP channel blockers. It is also known that protein kinase C (PKC) plays a key role in the induction and maintenance of preconditioning. To look for possible mechanistic links between these 2 sets of observations, we measured mitochondrial matrix redox

Toshiaki Sato; Brian O'Rourke; Eduardo Marban

235

Molecular Mechanisms Mediating Inhibition of G Protein-coupled Inwardly-rectifying K+ Channels  

Microsoft Academic Search

Neuronal G protein-coupled inwardly-rectifying po- tassium channels (GIRKs, Kir3.x) can be activated or inhibited by distinct classes of receptors (G?i\\/o and G?q\\/11-coupled, respectively), providing dynamic regulation of neuronal excitability.In this mini-review, we highlight findings from our laboratory in which we used a mammalian heterologous expression system to address mechanisms of GIRK channel regulation by G? and G?? subunits.We found that,

Qiubo Lei; Miller B. Jones; Edmund M. Talley; James C. Garrison; Douglas A. Bayliss

236

Membrane Incorporation, Channel Formation, and Disruption of Calcium Homeostasis by Alzheimer's ?-Amyloid Protein  

PubMed Central

Oligomerization, conformational changes, and the consequent neurodegeneration of Alzheimer's ?-amyloid protein (A?P) play crucial roles in the pathogenesis of Alzheimer's disease (AD). Mounting evidence suggests that oligomeric A?Ps cause the disruption of calcium homeostasis, eventually leading to neuronal death. We have demonstrated that oligomeric A?Ps directly incorporate into neuronal membranes, form cation-sensitive ion channels (“amyloid channels”), and cause the disruption of calcium homeostasis via the amyloid channels. Other disease-related amyloidogenic proteins, such as prion protein in prion diseases or ?-synuclein in dementia with Lewy bodies, exhibit similarities in the incorporation into membranes and the formation of calcium-permeable channels. Here, based on our experimental results and those of numerous other studies, we review the current understanding of the direct binding of A?P into membrane surfaces and the formation of calcium-permeable channels. The implication of composition of membrane lipids and the possible development of new drugs by influencing membrane properties and attenuating amyloid channels for the treatment and prevention of AD is also discussed.

Kawahara, Masahiro; Ohtsuka, Isao; Yokoyama, Shoko; Kato-Negishi, Midori; Sadakane, Yutaka

2011-01-01

237

Preparation of semi-solid aluminum alloy slurry poured through a water-cooled serpentine channel  

NASA Astrophysics Data System (ADS)

A water-cooled serpentine channel pouring process was invented to produce semi-solid A356 aluminum alloy slurry for rheocasting, and the effects of pouring temperature and circulating cooling water flux on the microstructure of the slurry were investigated. The results show that at the pouring temperature of 640-680°C and the circulating cooling water flux of 0.9 m3/h, the semi-solid A356 aluminum alloy slurry with spherical primary ?(Al) grains can be obtained, whose shape factors are between 0.78 and 0.86 and the grain diameter can reach 48-68 ?m. When the pouring temperatures are at 660-680°C, only a very thin solidified shell remains inside the serpentine channel and can be removed easily. When the serpentine channel is cooled with circulating water, the microstructure of the semi-solid slurry can be improved, and the serpentine channel is quickly cooled to room temperature after the completion of one pouring. In terms of the productivity of the special equipment, the water-cooled serpentine channel is economical and efficient.

Chen, Zheng-Zhou; Mao, Wei-Min; Wu, Zong-Chuang

2012-01-01

238

Mechanisms underlying the protein-kinase mediated regulation of the HERG potassium channel synthesis  

PubMed Central

The HERG (human ether-a-go-go related gene) potassium channel aids in repolarization of the cardiomyocyte membrane at the end of each action potential. We have previously shown that sustained protein kinase A or C (PKA and PKC) activity specifically enhances channel synthesis over the course of hours to days in heterologous expression and cardiac myocytes. The kinase-mediated augmentation of the channel is post-transcriptional and occurs near or at the endoplasmic reticulum. Here we report our further investigations into the mechanisms of kinase-mediated augmentation of HERG channel protein. We show that HERG channel phosphorylation alone is not sufficient for the PKA-dependent increase to occur. In vitro translation studies indicate that an additional factor is required for the process. Pharmacologic inhibitors suggest that the channel augmentation is not due to kinase-mediated alteration in proteasome or lysosome activity. PKA activation had no effect on stability of HERG mRNA and polyribosomal profiling showed that kinase activity did not elevate translation from low to high rates. Transcriptional inhibition results suggest that the additional cellular factor is a PKA-regulated protein. Together, these findings suggest that PKA-mediated augmentation of HERG abundance is more complex than previously appreciated involving enhancement of already active translation rates, phosphorylation of the channel protein and at least one other cAMP/PKA-responsive protein. Further exploration of molecular components of this regulatory pathway will be necessary to determine exact mechanism and the biomedical impact of this process in vivo.

Krishnan, Yamini; Li, Yan; Zheng, Renjian; Kanda, Vikram; McDonald, Thomas V.

2012-01-01

239

The use of dansyl-calmodulin to study interactions with channels and other proteins.  

PubMed

Steady-state fluorescence spectroscopy is a biophysical technique widely employed to characterize -interactions between proteins in vitro. Only a few proteins naturally fluoresce in cells, but by covalently attaching fluorophores virtually all proteins can be monitored. One of the first extrinsic fluorescent probes to be developed, and that is still in use, is dansyl chloride. We have used this method to monitor the interaction of a variety of proteins, including ion channels, with the Ca(2+)-dependent regulatory protein calmodulin. Here we describe the preparation and use of dansyl-calmodulin (D-CaM). PMID:23529433

Alaimo, Alessandro; Malo, Covadonga; Areso, Pilar; Aloria, Kerman; Millet, Oscar; Villarroel, Alvaro

2013-01-01

240

Boiling Water Reactor Fuel Cycle Optimization for Prevention of Channel-Blade Interference  

SciTech Connect

A formal optimization method for eliminating the potential of Boiling Water Reactor channel-blade interference is presented within the context of fuel cycle design. The method is based on the use of threshold constraints on blade force as penalty terms within an objective function that are employed as part of a search algorithm. Results demonstrate the effectiveness of the constraint formulation in eliminating channel-blade interference as part of the design of the core loading and operational strategy. (authors)

Kropaczek, David J.; Karve, Atul A.; Oyarzun, Christian C.; Asgari, Mehdi [Global Nuclear Fuel - Americas, P.O. Box 780, M/C F12, Wilmington, N.C. 28402 (United States); Tusar, James J. [Exelon Corporation, 200 Exelon Way, KSA 2-N, Kennett Square, PA 19348 (United States)

2006-07-01

241

Detection of tropical deep convective clouds from AMSU-B water vapor channels measurements  

Microsoft Academic Search

Methods to detect tropical deep convective clouds and convective overshooting from measurements at the three water vapor channels (183.3 +\\/- 1, 183.3 +\\/- 3, and 183.3 +\\/- 7 GHz) of the Advanced Microwave Sounding Unit-B (AMSU-B) are presented. Thresholds for the brightness temperature differences between the three channels are suggested as criterion to detect deep convective clouds, and an order

Gang Hong; Georg Heygster; Jungang Miao; Klaus Kunzi

2005-01-01

242

Detection of tropical deep convective clouds from AMSU-B water vapor channels measurements  

Microsoft Academic Search

Methods to detect tropical deep convective clouds and convective overshooting from measurements at the three water vapor channels (183.3 ± 1, 183.3 ± 3, and 183.3 ± 7 GHz) of the Advanced Microwave Sounding Unit-B (AMSU-B) are presented. Thresholds for the brightness temperature differences between the three channels are suggested as criterion to detect deep convective clouds, and an order

Gang Hong; Georg Heygster; Jungang Miao; Klaus Kunzi

2005-01-01

243

PEDV ORF3 encodes an ion channel protein and regulates virus production.  

PubMed

Several studies suggest that the open reading frame 3 (ORF3) gene of porcine epidemic diarrhea virus (PEDV) is related to viral infectivity and pathogenicity, but its function remains unknown. Here, we propose a structure model of the ORF3 protein consisting of four TM domains and forming a tetrameric assembly. ORF3 protein can be detected in PEDV-infected cells and it functions as an ion channel in both Xenopus laevis oocytes and yeast. Mutation analysis showed that Tyr170 in TM4 is important for potassium channel activity. Furthermore, viral production is reduced in infected Vero cells when ORF3 gene is silenced by siRNA. Interestingly, the ORF3 gene from an attenuated PEDV encodes a truncated protein with 49 nucleotide deletions, which lacks the ion channel activity. PMID:22245155

Wang, Kai; Lu, Wei; Chen, Jianfei; Xie, Shiqi; Shi, Hongyan; Hsu, Haojen; Yu, Wenjing; Xu, Ke; Bian, Chao; Fischer, Wolfgang B; Schwarz, Wolfgang; Feng, Li; Sun, Bing

2012-01-11

244

Pore waters regulate ion permeation in a calcium release-activated calcium channel.  

PubMed

The recent crystal structure of Orai, the pore unit of a calcium release-activated calcium (CRAC) channel, is used as the starting point for molecular dynamics and free-energy calculations designed to probe this channel's conduction properties. In free molecular dynamics simulations, cations localize preferentially at the extracellular channel entrance near the ring of Glu residues identified in the crystal structure, whereas anions localize in the basic intracellular half of the pore. To begin to understand ion permeation, the potential of mean force (PMF) was calculated for displacing a single Na(+) ion along the pore of the CRAC channel. The computed PMF indicates that the central hydrophobic region provides the major hindrance for ion diffusion along the permeation pathway, thereby illustrating the nonconducting nature of the crystal structure conformation. Strikingly, further PMF calculations demonstrate that the mutation V174A decreases the free energy barrier for conduction, rendering the channel effectively open. This seemingly dramatic effect of mutating a nonpolar residue for a smaller nonpolar residue in the pore hydrophobic region suggests an important role for the latter in conduction. Indeed, our computations show that even without significant channel-gating motions, a subtle change in the number of pore waters is sufficient to reshape the local electrostatic field and modulate the energetics of conduction, a result that rationalizes recent experimental findings. The present work suggests the activation mechanism for the wild-type CRAC channel is likely regulated by the number of pore waters and hence pore hydration governs the conductance. PMID:24101457

Dong, Hao; Fiorin, Giacomo; Carnevale, Vincenzo; Treptow, Werner; Klein, Michael L

2013-10-07

245

A mathematical model of water and sediment flow in open river channels  

Microsoft Academic Search

A one-dimensional mathematical model of water and sediment flow in open channels is proposed based on the forces influencing\\u000a a water stream and bottom and stream sediments. The equations of water and sediment flow are closed by the equations of continuity\\u000a of stream, velocity of particle motion in a stream, and the equation of balance of kinetic energy and moving

M. V. Shmakova; A. N. Kondrat’ev

2008-01-01

246

EFFECT OF WATER DEPTH AND AERATION ON A CONTACT MEDIA CHANNEL PURIFICATION PROCESS FOR WASTEWATER RECLAMATION  

Microsoft Academic Search

In this study, contact media channel purification process (CMCP) filled with honeycomb media was adopted to implement continuous flow experiments when aeration and water depth varied. The water depth was set at 0.2, 0.5 and 0.8 m, respectively. Three aeration values including 30, 50 and 70 m h-1 were operated at each water depth. The results indicated that the removal

Tzu-Yi Pai; Chwen-Jeng Tzeng; Chen-Lung Hsu; Yao-Sheng Tsai; Wen-Jui Hsu

247

The effect of protein dielectric coefficient on the ionic selectivity of a calcium channel  

NASA Astrophysics Data System (ADS)

Calcium-selective ion channels are known to have carboxylate-rich selectivity filters, a common motif that is primarily responsible for their high Ca2+ affinity. Different Ca2+ affinities ranging from micromolar (the L-type Ca channel) to millimolar (the ryanodine receptor channel) are closely related to the different physiological functions of these channels. To understand the physical mechanism for this range of affinities given similar amino acids in their selectivity filters, we use grand canonical Monte Carlo simulations to assess the binding of monovalent and divalent ions in the selectivity filter of a model Ca channel. We use a reduced model where the electolyte is modeled by hard-sphere ions embedded in a continuum dielectric solvent, while the interior of protein surrounding the channel is allowed to have a dielectric coefficient different from that of the electrolyte. The induced charges that appear on the protein/lumen interface are calculated by the induced charge computation method [Boda et al., Phys. Rev. E 69, 046702 (2004)]. It is shown that decreasing the dielectric coefficient of the protein attracts more cations into the pore because the protein's carboxyl groups induce negative charges on the dielectric boundary. As the density of the hard-sphere ions increases in the filter, Ca2+ is absorbed into the filter with higher probability than Na+ because Ca2+ provides twice the charge to neutralize the negative charge of the pore (both structural carboxylate oxygens and induced charges) than Na+ while occupying about the same space (the charge/space competition mechanism). As a result, Ca2+ affinity is improved an order of magnitude by decreasing the protein dielectric coefficient from 80 to 5. Our results indicate that adjusting the dielectric properties of the protein surrounding the permeation pathway is a possible way for evolution to regulate the Ca2+ affinity of the common four-carboxylate motif.

Boda, Dezs?; Valiskó, Mónika; Eisenberg, Bob; Nonner, Wolfgang; Henderson, Douglas; Gillespie, Dirk

2006-07-01

248

Studies on water retention and water release from some protein systems  

Microsoft Academic Search

The hydrogen-bond properties (WBI index), water retention and water release from the protein-water systems gluten-water, soya protein- water and casein-water, have been investigated using differential scanning calorimetry in the temperature range 223–423 K. The proteins were characterized by their isoelectric point, contents of carboxyl groups and sulfur-containing groups, and readiness of undergo chloromethylation. It was concluded that the marked difference

R. Silvonen; J. J. Lindberg; C. Seppälä; M. Ervasti; C. Hauta-Aho

1982-01-01

249

Structure and Energetics of Channel-Forming Protein-Polysaccharide Complexes Inferred via Computational Statistical Thermodynamics  

PubMed Central

The ion channel protein ?-hemolysin (?HL) forms supramolecular complexes with the polysaccharide ?-cyclodextrin (?CD). This system has potential uses in nanoscale device engineering. It has been found recently that ?CD formed longer- or shorter-lived complexes with some engineered ?HL mutants then with a wild type protein (Gu et al. J. Gen. Physiol. 2001, 118, 481–493). However, how changes in the protein sequence affect complex lifetime was not completely understood in part due to the lack of knowledge of structures of these metastable complexes. In this paper, we present an extensive molecular modeling study of the ?CD–?HL and selected mutant complexes to gain insights into the ?CD–?HL interaction mechanisms and to predict possible structures and energetics of the complexes. Thermodynamic integration (TI) and umbrella sampling (US) techniques (with the weighted histogram analysis method (WHAM)) were used to calculate the relative binding affinities of the complexes formed with the wild type ?HL and the M113N, M113E, M113A, and M113V mutants. Our results are in excellent agreement with experiment. While ?CD–M113N and ?CD–M113A complexes were stable in the configuration of the wild type complex, the equilibrium configuration of the ?CD–M113V and ?CD–M113E complexes was significantly different. In these cases, TI alone was insufficient to accurately calculate the corresponding free energy differences. By utilizing a TI/US combination in a novel manner, we were able to accurately calculate free energy changes in these flexible systems. The ?CD–M113A and ?CD–M113E complexes, which exhibited shorter lifetimes than other complexes in an experiment, in simulations exhibited greater flexibility and higher water solvation of the ?CD adapter. MD simulations of the ?CD–M113N complex with ?CD in a downward orientation were also performed.

Mamonova, Tatyana; Kurnikova, Maria

2007-01-01

250

Abscisic acid and 14-3-3 proteins control K channel activity in barley embryonic root.  

PubMed

Germination of seeds proceeds in general in two phases, an initial imbibition phase and a subsequent growth phase. In grasses like barley, the latter phase is evident as the emergence of the embryonic root (radicle). The hormone abscisic acid (ABA) inhibits germination because it prevents the embryo from entering and completing the growth phase. Genetic and physiological studies have identified many steps in the ABA signal transduction cascade, but how it prevents radicle elongation is still not clear. For elongation growth to proceed, uptake of osmotically active substances (mainly K(+)) is essential. Therefore, we have addressed the question of how the activity of K(+) permeable ion channels in the plasma membrane of radicle cells is regulated under conditions of slow (+ABA) and rapid germination (+fusicoccin). We found that ABA arrests radicle growth, inhibits net K(+) uptake and reduces the activity of K(+) (in) channels as measured with the patch-clamp technique. In contrast, fusicoccin (FC), a well-known stimulator of germination, stimulates radicle growth, net K(+) uptake and reduces the activity of K(+) (out) channels. Both types of channels are under the control of 14-3-3 proteins, known as integral components of signal transduction pathways and instrumental in FC action. Intriguingly, 14-3-3 affected both channels in an opposite fashion: whereas K(+) (in) channel activity was fully dependent upon 14-3-3 proteins, K(+) (out) channel activity was reduced by 14-3-3 proteins by 60%. Together with previous data showing that 14-3-3 proteins control the activity of the plasma membrane H(+)-ATPase, this makes 14-3-3 a prime candidate for molecular master regulator of the cellular osmo-pump. Regulation of the osmo-pump activity by ABA and FC is an important mechanism in controlling the growth of the embryonic root during seed germination. PMID:15610348

van den Wijngaard, Paul W J; Sinnige, Mark P; Roobeek, Ilja; Reumer, Annet; Schoonheim, Peter J; Mol, Jos N M; Wang, Mei; De Boer, Albertus H

2005-01-01

251

Effects of calcium channel blockers on stress protein synthesis in cardiac myocytes.  

PubMed

The detection of "stress proteins," certain protein groups of 70 or 30 kDa molecular weight synthesized de novo under stress conditions, serves as an assay for monitoring cellular toxicity. Typical toxins inducing stress protein formation in cardiac myocytes are CdCl2 and H2O2. The synthesis of 68, 71, and 30 kDa stress proteins is evoked by CdCl2, and H2O2 stimulates the formation of a 30 kDa protein. When fetal mouse myocardial cells are incubated first with CdCl2 and then with H2O2 or vice versa, an additive effect on stress protein synthesis can be documented. The calcium antagonists diltiazem, verapamil, and nifedipine, at concentrations above 0.05 mg/ml, stimulate the de novo synthesis of a 30 kDa stress protein. After preincubation of the cardiac myocytes with slow calcium channel blockers, the synthesis of the 70 kDa stress protein family evoked by CdCl2 is reduced. In contrast to the increased stress protein synthesis after heart cells are exposed to toxins, preincubation with calcium antagonists reduces the formation of certain stress proteins. These results indicate an interference of calcium channel blocking drugs with stress protein formation in cultured mouse myocardial cells. PMID:1713996

Löw-Friedrich, I; Schoeppe, W

1991-05-01

252

cDNA cloning of a functional water channel from toad urinary bladder epithelium.  

PubMed

A cDNA was cloned from the epithelium of toad (Bufo marinas) urinary bladder, based on homology to the mammalian aquaporins (AQP). The cDNA [947 base pairs (bp), identified as AQP-t1] encoded a 272-amino acid protein with 76% identity to mammalian aquaporin-1 (AQP-1) and 88% identity to frog water channel FA-CHIP. AQP-t1 cDNA was nearly identical to a fragment of a nonfunctional cDNA cloned recently from toad bladder ["AQP-TB"; J. Siner, A. Paredes, C. Hosselet, T. Hammond, K. Strange, and H.W. Harris, Am. J. Physiol. 270 (Cell Physiol. 39): C372-C381, 1996], except for reading frame shifts at bp 253, 264, and 682, two single amino acid deletions, a different 3'-coding sequence downstream from bp 786, and a different 5' sequence upstream from bp 9. Water permeability (Pf) in Xenopus laevis oocytes expressing AQP-t1 cRNA was strongly increased from (0.83 +/- 0.06) x 10(-3) cm/s (water-injected control) to (17 +/- 4) x 10(-3) cm/s, with 80% inhibition by 0.3 mM HgCl2; glycerol and urea permeabilities were not increased. Northern blot analysis showed a single AQP-t1 mRNA of 2.8 kb in eye > lung > urinary bladder > skin > stomach approximately heart, brain, and intestine. AQP-t1 mRNA expression was not changed by a 3-day dehydration of toads or an 8-h stimulation of Pf in isolated bladders by forskolin. These results indicate that the epithelium of toad urinary bladder expresses a functional homologue of AQP-1 and FA-CHIP that is probably not vasopressin regulated. PMID:8944654

Ma, T; Yang, B; Verkman, A S

1996-11-01

253

H^- and D^- channels of Dissociative Electron Attachment to water molecules  

NASA Astrophysics Data System (ADS)

A COLTRIM technique is modified to measure the kinetic energy and angular distribution of H^- and D^- ions arising from dissociative electron attachment to water and heavy water molecules. A low energy pulsed electron, an effusive water target, a pulsed extraction plate are used in combination with the COLTRIMS spectrometer. The spectrometer carries an electrostatic lens system to compensate the effusiveness of the target. This technique is applied to study the H^- and D^- channels in the three Feshbach resonances of water and heavy water anion. The measured kinetic energy release will give the energy partitioning among the fragments, and the means to identify the two-body and three-body breakup channels. The angular distribution of the H^-(D^-) ions with respect to the electron beam is found to reflect well the breakup dynamics of the H2O^- at the dissociation. The experimental results are compared with the theoretical predictions.

Adaniya, Hidehito; Rudek, Benedikt; Osipov, Timur; Lee, Sun; Weber, Thorsten; Hertlein, Marcus; Schoeffler, Markus; Prior, Mike; Belkacem, Ali

2009-05-01

254

A virus-encoded potassium ion channel is a structural protein in the chlorovirus Paramecium bursaria chlorella virus 1 virion.  

PubMed

Most chloroviruses encode small K(+) channels, which are functional in electrophysiological assays. The experimental finding that initial steps in viral infection exhibit the same sensitivity to channel inhibitors as the viral K(+) channels has led to the hypothesis that the channels are structural proteins located in the internal membrane of the virus particles. This hypothesis was questioned recently because proteomic studies failed to detect the channel protein in virions of the prototype chlorovirus Paramecium bursaria chlorella virus 1 (PBCV-1). Here, we used a mAb raised against the functional K(+) channel from chlorovirus MA-1D to search for the viral K(+) channel in the virus particle. The results showed that the antibody was specific and bound to the tetrameric channel on the extracellular side. The antibody reacted in a virus-specific manner with protein extracts from chloroviruses that encoded channels similar to that from MA-1D. There was no cross-reactivity with chloroviruses that encoded more diverse channels or with a chlorovirus that lacked a K(+) channel gene. Together with electron microscopic imaging, which revealed labelling of individual virus particles with the channel antibody, these results establish that the viral particles contain an active K(+) channel, presumably located in the lipid membrane that surrounds the DNA in the mature virions. PMID:23918407

Romani, Giulia; Piotrowski, Adrianna; Hillmer, Stefan; Gurnon, James; Van Etten, James L; Moroni, Anna; Thiel, Gerhard; Hertel, Brigitte

2013-08-05

255

The protein-conducting channel in the membrane of the endoplasmic reticulum is open laterally toward the lipid bilayer  

Microsoft Academic Search

Lipids and proteins were found to contact a nascent type II membrane protein, as well as a nascent secretory protein, during their insertion into the membrane of the endoplasmic reticulum. This suggests that the protein-conducting channel is open laterally toward the lipid bilayer during an early stage of protein insertion. Contact to lipids was confined to the hydrophobic core region

Bruno Martoglio; Michael W. Hofmann; Josef Brunner; Bernhard Dobberstein

1995-01-01

256

Activation of protein kinase C inhibits calcium-activated potassium channels in rat pituitary tumour cells.  

PubMed

1. The regulation of large-conductance, calcium- and voltage-dependent potassium (BK) channels by protein kinase C (PKC) was investigated in clonal rat anterior pituitary cells (GH4C1), which were voltage clamped at -40 mV in a physiological potassium gradient through amphotericin-perforated patches. 2. Maximal activation of PKC by 100 nM phorbol 12, 13-dibutyrate (PdBu) almost completely inhibited the voltage-activated outward current through BK channels. In contrast PdBu had no significant effect on the residual outward current after block of BK channels with 2 mM TEA or 30 nM charybdotoxin. In single-channel recordings from cell-attached patches, PdBu reduced the open probability of BK channels more than eightfold with no significant effect on mean open lifetime or unitary conductance. 3. The effects of PdBu on BK channels were not mimicked by the 4 alpha-isomer, which does not activate PKC, and were blocked almost completely by 25 microM chelerythrine, a specific, noncompetitive PKC inhibitor. 4. PdBu had no significant effect on the amplitude of the pharmacologically isolated, high voltage-activated calcium current. 5. Inhibition of BK channel activity by PKC provides the first molecular mechanism linking hormonal activation of phospholipase C to sustained excitability in pituitary cells. PMID:8799890

Shipston, M J; Armstrong, D L

1996-06-15

257

Vertical arrival structure of shipping noise in deep water channels  

Microsoft Academic Search

In passive sonar systems, knowledge of low-frequency shipping noise is significant for target detection performance. However, an accurate model for the shipping noise structure is difficult to obtain, because of the varying distributions of ships and complicated underwater environment. This work characterizes low-frequency distant shipping noise observed in deep water environments as a function of receiver depth and vertical arrival

Zizheng Li; Lisa M. Zurk; Barry Ma

2010-01-01

258

Inhibition of G protein-activated inwardly rectifying K+ channels by fluoxetine (Prozac)  

PubMed Central

The effects of fluoxetine, a commonly used antidepressant drug, on G protein-activated inwardly rectifying K+ channels (GIRK, Kir3) were investigated using Xenopus oocyte expression assays. In oocytes injected with mRNAs for GIRK1/GIRK2, GIRK2 or GIRK1/GIRK4 subunits, fluoxetine reversibly reduced inward currents through the basal GIRK activity. The inhibition by fluoxetine showed a concentration-dependence, a weak voltage-dependence and a slight time-dependence with a predominant effect on the instantaneous current elicited by voltage pulses and followed by slight further inhibition. Furthermore, in oocytes expressing GIRK1/2 channels and the cloned Xenopus A1 adenosine receptor, GIRK current responses activated by the receptor were inhibited by fluoxetine. In contrast, ROMK1 and IRK1 channels in other Kir channel subfamilies were insensitive to fluoxetine. The inhibitory effect on GIRK channels was not obtained by intracellularly applied fluoxetine, and not affected by extracellular pH, which changed the proportion of the uncharged to protonated fluoxetine, suggesting that fluoxetine inhibits GIRK channels from the extracellular side. The GIRK currents induced by ethanol were also attenuated in the presence of fluoxetine. We demonstrate that fluoxetine, at low micromolar concentrations, inhibits GIRK channels that play an important role in the inhibitory regulation of neuronal excitability in most brain regions and the heart rate through activation of various G-protein-coupled receptors. The present results suggest that inhibition of GIRK channels by fluoxetine may contribute to some of its therapeutic effects and adverse side effects, particularly seizures in overdose, observed in clinical practice.

Kobayashi, Toru; Washiyama, Kazuo; Ikeda, Kazutaka

2003-01-01

259

A kinetic analysis of protein transport through the anthrax toxin channel  

PubMed Central

Anthrax toxin is composed of three proteins: a translocase heptameric channel, (PA63)7, formed from protective antigen (PA), which allows the other two proteins, lethal factor (LF) and edema factor (EF), to translocate across a host cell’s endosomal membrane, disrupting cellular homeostasis. (PA63)7 incorporated into planar phospholipid bilayer membranes forms a channel capable of transporting LF and EF. Protein translocation through the channel can be driven by voltage on a timescale of seconds. A characteristic of the translocation of LFN, the N-terminal 263 residues of LF, is its S-shaped kinetics. Because all of the translocation experiments reported in the literature have been performed with more than one LFN molecule bound to most of the channels, it is not clear whether the S-shaped kinetics are an intrinsic characteristic of translocation kinetics or are merely a consequence of the translocation in tandem of two or three LFNs. In this paper, we show both in macroscopic and single-channel experiments that even with only one LFN bound to the channel, the translocation kinetics are S shaped. As expected, the translocation rate is slower with more than one LFN bound. We also present a simple electrodiffusion model of translocation in which LFN is represented as a charged rod that moves subject to both Brownian motion and an applied electric field. The cumulative distribution of first-passage times of the rod past the end of the channel displays S-shaped kinetics with a voltage dependence in agreement with experimental data.

Kienker, Paul K.; Briggs, Stephen W.; Finkelstein, Alan

2011-01-01

260

Engineering of an E. coli outer membrane protein FhuA with increased channel diameter  

PubMed Central

Background Channel proteins like FhuA can be an alternative to artificial chemically synthesized nanopores. To reach such goals, channel proteins must be flexible enough to be modified in their geometry, i.e. length and diameter. As continuation of a previous study in which we addressed the lengthening of the channel, here we report the increasing of the channel diameter by genetic engineering. Results The FhuA ?1-159 diameter increase has been obtained by doubling the amino acid sequence of the first two N-terminal ?-strands, resulting in variant FhuA ?1-159 Exp. The total number of ?-strands increased from 22 to 24 and the channel surface area is expected to increase by ~16%. The secondary structure analysis by circular dichroism (CD) spectroscopy shows a high ?-sheet content, suggesting the correct folding of FhuA ?1-159 Exp. To further prove the FhuA ?1-159 Exp channel functionality, kinetic measurement using the HRP-TMB assay (HRP = Horse Radish Peroxidase, TMB = 3,3',5,5'-tetramethylbenzidine) were conducted. The results indicated a 17% faster diffusion kinetic for FhuA ?1-159 Exp as compared to FhuA ?1-159, well correlated to the expected channel surface area increase of ~16%. Conclusion In this study using a simple "semi rational" approach the FhuA ?1-159 diameter was enlarged. By combining the actual results with the previous ones on the FhuA ?1-159 lengthening a new set of synthetic nanochannels with desired lengths and diameters can be produced, broadening the FhuA ?1-159 applications. As large scale protein production is possible our approach can give a contribution to nanochannel industrial applications.

2011-01-01

261

GABA B Receptor Coupling to G-proteins and Ion Channels  

Microsoft Academic Search

GABAB receptors have been found to play a key role in regulating membrane excitability and synaptic transmission in the brain. The GABAB receptor is a G-protein coupled receptor (GPCR) that associates with a subset of G-proteins (pertussis toxin sensitive Gi\\/o family), that in turn regulate specific ion channels and trigger cAMP cascades. In this review, we describe the relationships between

Claire L. Padgett; Paul A. Slesinger

2010-01-01

262

Intrinsically disordered proteins aggregate at fungal cell-to-cell channels and regulate intercellular connectivity  

PubMed Central

Like animals and plants, multicellular fungi possess cell-to-cell channels (septal pores) that allow intercellular communication and transport. Here, using a combination of MS of Woronin body-associated proteins and a bioinformatics approach that identifies related proteins based on composition and character, we identify 17 septal pore-associated (SPA) proteins that localize to the septal pore in rings and pore-centered foci. SPA proteins are not homologous at the primary sequence level but share overall physical properties with intrinsically disordered proteins. Some SPA proteins form aggregates at the septal pore, and in vitro assembly assays suggest aggregation through a nonamyloidal mechanism involving mainly ?-helical and disordered structures. SPA loss-of-function phenotypes include excessive septation, septal pore degeneration, and uncontrolled Woronin body activation. Together, our data identify the septal pore as a complex subcellular compartment and focal point for the assembly of unstructured proteins controlling diverse aspects of intercellular connectivity.

Lai, Julian; Koh, Chuan Hock; Tjota, Monika; Pieuchot, Laurent; Raman, Vignesh; Chandrababu, Karthik Balakrishna; Yang, Daiwen; Wong, Limsoon; Jedd, Gregory

2012-01-01

263

Molecular Linkage of TRP Proteins to Smooth Muscle Receptor-Operated Ca 2+ Permeable Cationic Channels  

Microsoft Academic Search

The molecular mechanisms underlying Ca2+ entry evoked by cell surface receptors in smooth muscle have long been enigmatic, but an important breakthrough has been made by recent investigations on mammalian homologues of Drosophila transient receptor potential (TRP) protein. There is now growing evidence that TRPC6 plays an integrative role in vascular tone regulation, Ca2+ entry channels activated by the sympathetic

Ryuji Inoue

2003-01-01

264

REST: A mammalian silencer protein that restricts sodium channel gene expression to neurons  

Microsoft Academic Search

Expression of the type II voltage-dependent sodium channel gene is restricted to neurons by a silencer element active in nonneuronal cells. We have cloned cDNA coding for a transcription factor (REST) that binds to this silencer element. Expression of a recombinant REST protein confers the ability to silence type II reporter genes in neuronal cell types lacking the native REST

Jayhong A Chong; José Tapia-Ramirez; Sandra Kim; Juan J Toledo-Aral; Yingcong Zheng; Michael C Boutros; Yelena M Altshuller; Michael A Frohman; Susan D Kraner; Gail Mandel

1995-01-01

265

Rapid beta Adrenergic Modulation of Cardiac Calcium Channel Currents by a Fast G Protein Pathway  

Microsoft Academic Search

beta -Adrenergic agonists activate the G protein, Gs, which stimulates cardiac calcium currents by both cytoplasmic, indirect and membrane-delimited, direct pathways. To test whether beta -adrenergic agonists might use both pathways in the heart, isoproterenol was rapidly applied to cardiac myocytes, resulting in a biphasic increase in cardiac calcium channel currents that had time constants of 150 milliseconds and 36

Atsuko Yatani; Arthur M. Brown

1989-01-01

266

The alpha Subunit of the GTP Binding Protein Gk Opens Atrial Potassium Channels  

Microsoft Academic Search

Guanine nucleotide binding (G) proteins (subunit composition alpha beta gamma ) dissociate on activation with guanosine triphosphate (GTP) analogs and magnesium to give alpha -guanine nucleotide complexes and free beta gamma subunits. Whether the opening of potassium channels by the recently described Gk in isolated membrane patches from mammalian atrial myocytes was mediated by the alpha k subunit or beta

Juan Codina; Atsuko Yatani; Dagoberto Grenet; Arthur M. Brown; Lutz Birnbaumer

1987-01-01

267

Inhibition of G Protein-Activated Inwardly Rectifying K+ Channels by Different Classes of Antidepressants  

Microsoft Academic Search

Various antidepressants are commonly used for the treatment of depression and several other neuropsychiatric disorders. In addition to their primary effects on serotonergic or noradrenergic neurotransmitter systems, antidepressants have been shown to interact with several receptors and ion channels. However, the molecular mechanisms that underlie the effects of antidepressants have not yet been sufficiently clarified. G protein-activated inwardly rectifying K+

Toru Kobayashi; Kazuo Washiyama; Kazutaka Ikeda

2011-01-01

268

Signal variability in shallow-water sound channels  

Microsoft Academic Search

Coherence of broad-band acoustic waves for mid-to-high frequencies (0.6-18 kHz) is obtained for a very shallow-water (15-m-deep) waveguide over a wide band of environmental conditions and for a source-receiver range of 387 m. Temporal behavior is sampled at two different rates: one that resolves at fractions of a second over intermittent periods of 40 s and another that resolves at

M. Badiey; Yongke Mu; J. A. Simmen; S. E. Forsythe

2000-01-01

269

Do zebrafish Rh proteins act as dual ammonia-CO2 channels?  

PubMed

Transfer of the small gaseous molecules CO2 and NH3 across biological membranes, long thought to occur solely by simple diffusion, is now known to be facilitated by members of two multigene families: aquaporins (AQP) and rhesus (Rh) proteins. Although it is accepted that AQP1 and Rh proteins are involved in CO2 and NH3 transfer, respectively, the idea that a single channel can exhibit selectivity for both gases is controversial. Indeed, studies using the same in vitro model (human red blood cells) have provided evidence both for and against a role for Rh proteins as CO2 channels. Thus, this study was initiated to provide in vivo evidence for a dual function of Rh proteins as ammonia and CO2 channels. Here, we show that in zebrafish (Danio rerio), direct ammonia-CO2 competition experiments in adults or translational knockdowns of Rh proteins in larvae affects both ammonia and CO2 excretion. These results suggest that Rh proteins in zebrafish may be common pathways for transport of ammonia and CO2. PMID:20683854

Perry, Steve F; Braun, Marvin H; Noland, Marie; Dawdy, John; Walsh, Patrick J

2010-11-01

270

THE ROLE OF WATER IN PROTEIN-DNA RECOGNITION  

Microsoft Academic Search

? Abstract Is it by design or by default that water molecules are observed at the interfaces of some protein-DNA complexes? Both experimental and theoretical studies on the thermodynamics of protein-DNA binding overwhelmingly support the extended hydrophobic view that water release from interfaces favors binding. Structural and en- ergy analyses indicate that the waters that remain at the interfaces of

B. Jayaram; Tarun Jain

2004-01-01

271

Expression and immunolocalization of the aquaporin-8 water channel in rat gastrointestinal tract.  

PubMed

A remarkable amount, of water is transported in the gastrointestinal (GI) organs to fulfil the secretory and absorptive functions of the GI tract. However, the molecular basis of water movement in the GI epithelial barriers is still poorly known. Important clues about the mechanisms by which water is transported in the GI tract were provided by the recent identification of multiple aquaporin water channels expressed in GI tissues. Here we define the mRNA and protein expression and the cellular and subcellular distribution of aquaporin-8 (AQP8) in the rat GI tract. By semi-quantitative RT-PCR the AQP8 mRNA was detected in duodenum, proximal jejunum, proximal colon, rectum, pancreas and liver and, to a lesser extent, in stomach and distal colon. Immunohistochemistry using affinity-purified antibodies revealed AQP8 staining in the absorptive epithelial cells of duodenum, proximal jejunum, proximal colon and rectum where labeling was largely intracellular and confined to the subapical cytoplasm. Confirming previous results, AQP8 staining was seen at the apical pole of pancreatic acinar cells. Interestingly, both light and immunoelectron microscopy analyses showed AQP8 reactivity in liver where labeling was associated to hepatocyte intracellular vesicles and over the plasma membrane delimiting the bile canaliculi. A complex pattern was observed by immunoblotting with total membranes of the above GI organs incubated with affinity-purified anti-AQP8 antibodies which revealed multiple bands with molecular masses ranging between 28 and 45 kDa. This immunoblotting pattern was not modified after deglycosylation with N-glycosidase F except the 34-kDa band of liver that, as already reported, was partially down-shifted to 28 kDa. No bands were detected after preadsorption of the anti-AQP8 antibodies with the immunizing peptide. The cellular and subcellular distribution of AQP8 suggest physiological roles for this aquaporin in the absorption of water in the intestine and the secretion of bile and pancreatic juice in liver and pancreas, respectively. The large intracellular expression of AQP8 may indicate its recycling between the cytoplasmic compartment and the plasma membrane. The cytoplasmic localization observed may also relate to the involvement of AQP8 in processes of intracellular osmoregulation. PMID:11824790

Calamita, G; Mazzone, A; Bizzoca, A; Cavalier, A; Cassano, G; Thomas, D; Svelto, M

2001-11-01

272

Properties of channels reconstituted from the major intrinsic protein of lens fiber membranes.  

PubMed

Detergent-solubilized plasma membrane protein of either adult bovine or calf lens and high-performance liquid chromatography-purified major intrinsic protein (MIP) of the lens were reconstituted into unilamellar vesicles and planar lipid bilayers. Freeze-fracture studies showed that the density of intramembrane particles in the vesicles was proportional to the protein/lipid ratio. At high ratios, these particles crystallized into tetragonal arrays as does MIP in lens fibers. Channels induced by either purified MIP or detergent-solubilized protein had essentially identical properties. The conductance of multichannel membranes was maximal near 0 mV and decreased to 0.49 +/- 0.08 of the maximum value at voltages greater than 80 mV. The dependence of the conductance on voltage was well fit by a two-state Boltzmann distribution. Voltage steps greater than 30 mV elicited an ohmic current step followed by a slow (seconds) biexponential decrease. The amplitudes and time constants depended on the magnitude but not the sign of the voltage. Steps from 100 mV to voltages less than 30 mV caused the channels to open exponentially with a millisecond time constant. Analysis of latency to first closure after a voltage step gave nearly the same time constants as multichannel kinetics. Single-channel conductance is proportional to salt concentration from 0.1 to 1.0 M in KCl. In 0.1M KCl, the channel had two preferred conductance states with amplitudes of 380 and 160 pS, as well as three additional substates. Multi- and single-channel data suggest that the channel has two kinetically important open states. The channel is slightly anion selective. The properties of the channel do not vary appreciably from pH 7.4 to 5.8 or from pCa 7 to 2. We propose that a channel with these properties could contribute to maintenance of lens transparency and fluid balance. PMID:1700061

Ehring, G R; Zampighi, G; Horwitz, J; Bok, D; Hall, J E

1990-09-01

273

G-Protein Inhibition of N- and P\\/Q-Type Calcium Channels: Distinctive Elementary Mechanisms and Their Functional Impact  

Microsoft Academic Search

Voltage-dependent G-protein inhibition of presynaptic Ca 21 channels is a key mechanism for regulating synaptic efficacy. G-protein bg subunits produce such inhibition by binding to and shifting channel opening patterns from high to low open probability regimes, known respectively as \\

Henry M. Colecraft; David L. Brody; David T. Yue

2000-01-01

274

Induction of aquaporin-4 water channel mRNA after focal cerebral ischemia in rat  

Microsoft Academic Search

Aquaporin-4 (AQP4) is a member of a water-selective channel aquaporin-family and mainly expressed in the several structures of the brain and in the collecting duct of the kidney. Here we show its functional involvement in the water homeostasis of the ischemic brain. The expression of AQP4–mRNA is increased in the peri-infarcted cortex during the observation period (?7 days) after MCA-occlusion,

Masaaki Taniguchi; Toshihide Yamashita; Eiji Kumura; Michio Tamatani; Akihiro Kobayashi; Takashi Yokawa; Motohiko Maruno; Amami Kato; Takanori Ohnishi; Eiji Kohmura; Masaya Tohyama; Toshiki Yoshimine

2000-01-01

275

Biogas production from water hyacinth and channel grass used for phytoremediation of industrial effluents  

Microsoft Academic Search

The paper reports on the biogas production from water hyacinth (Eichhornia crassipes) and channel grass (Vallisneria spiralis) employed separately for phytoremediation of lignin and metal-rich pulp and paper mill and highly acidic distillery effluents. These plants eventually grow well in diluted effluent up to 40% (i.e., 2.5-times dilution with deionized water) and often take up metals and toxic materials from

V Singhal; J. P. N Rai

2003-01-01

276

Probing the water permeability of ROMK1 and amphotericin B channels using Xenopus oocytes  

Microsoft Academic Search

Water permeability of ion channels in the plasma membrane of Xenopus oocytes was studied by simultaneously measuring the membrane conductance under two-electrode voltage-clamp and the cell size by video-imaging technique. The basal level of osmotic water permeability of oocyte plasma membrane was 15.9±0.98?m\\/s (SE, n=5). Extracellular application of pore-forming antibiotic amphotericin B at 5?M developed macroscopic conductance of 995±70?S (n=5)

Ravshan Z Sabirov; Shigeru Morishima; Yasunobu Okada

1998-01-01

277

Basolateral targeting and microtubule-dependent transcytosis of the aquaporin-2 water channel.  

PubMed

The aquaporin-2 (AQP2) water channel relocates mainly to the apical plasma membrane of collecting duct principal cells after vasopressin (VP) stimulation. AQP2 transport to this membrane domain is assumed to be a direct route involving recycling of intracellular vesicles. However, basolateral plasma membrane expression of AQP2 is observed in vivo in principal cells. Here, we asked whether there is a transcytotic pathway of AQP2 trafficking between apical and basolateral membranes. We used MDCK cells in which AQP2 normally accumulates apically after VP exposure. In contrast, both site-specific biotinylation and immunofluorescence showed that AQP2 is strongly accumulated in the basolateral membrane, along with the endocytic protein clathrin, after a brief cold shock (4°C). This suggests that AQP2 may be constitutively targeted to basolateral membranes and then retrieved by clathrin-mediated endocytosis at physiological temperatures. Rab11 does not accumulate in basolateral membranes after cold shock, suggesting that the AQP2 in this location is not associated with Rab11-positive vesicles. After rewarming (37°C), basolateral AQP2 staining is diminished and it subsequently accumulates at the apical membrane in the presence of VP/forskolin, suggesting that transcytosis can be followed by apical insertion of AQP2. This process is inhibited by treatment with colchicine. Our data suggest that the cold shock procedure reveals the presence of microtubule-dependent AQP2 transcytosis, which represents an indirect pathway of apical AQP2 delivery in these cells. Furthermore, our data indicate that protein polarity data obtained from biotinylation assays, which require cells to be cooled to 4°C during the labeling procedure, should be interpreted with caution. PMID:23015545

Yui, Naofumi; Lu, Hua A J; Chen, Ying; Nomura, Naohiro; Bouley, Richard; Brown, Dennis

2012-09-26

278

Regulation of the ABA-sensitive Arabidopsis potassium channel gene GORK in response to water stress  

Microsoft Academic Search

The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we

D. Becker; S. Hoth; P. Ache; S. Wenkel; M. R. G. Roelfsema; O. Meyerhoff; W. Hartung; R. Hedrich

2003-01-01

279

Modification of cardiac sodium channels by carboxyl reagents. Trimethyloxonium and water-soluble carbodiimide  

Microsoft Academic Search

In TFX-sensitive nerve and skeletal muscle Na + channels, selective modification of external carboxyl groups with trimethyloxonium (TMO) or water- soluble carbodiimide (WSC) prevents voltage-dependent Ca z+ block, reduces uni- tary conductance, and decreases guanidinium toxin affinity. In the case of TMO, it has been suggested that all three effects result from modification of a single carboxyl group, which causes

SAMUEL C. DUDLEY; CLIVE M. BAUMGARTEN

1993-01-01

280

Impact of multiple submarine channels on the descent of dense water at high latitudes  

Microsoft Academic Search

A three-dimensional numerical hydrodynamic model is applied to examine the impact of multiple submarine channels (<10 km across, <100 m deep), common to most continental margins of the ocean, on the descent of dense water at high latitudes. The model consists of an ocean bottom layer of constant height that follows variable bottom topography under constant vertical grid spacing. An

Jochen Kämpf

2000-01-01

281

Effects of Channel Catfish Farming on Water Quality and Flow in an Alabama Stream  

Microsoft Academic Search

Big Prairie Creek, Hale County, Alabama, receives overflow and draining effluent from about 5,000 ha of channel catfish, Ictalurus punctatus, ponds. Tributary streams receiving effluent directly from ponds were higher in concentrations of suspended solids, turbidity, nutrients, and biochemical oxygen demand than Big Prairie Creek, and these variables increased from upstream to downstream stations in Big Prairie Creek. Nevertheless, water

Orawan Silapajarn; Claude E. Boyd

2005-01-01

282

Gating of the TrkH Ion Channel by its Associated RCK Protein, Trka  

PubMed Central

TrkH belongs to a superfamily of K+ transport proteins required for growth of bacteria in low external K+ concentrations. The crystal structure of TrkH from Vibrio parahaemolyticus showed that TrkH resembles a K+ channel, and may have a gating mechanism substantially different from K+ channels. TrkH assembles with TrkA, a cytosolic protein comprising two Regulate-the-Conductance-of-K+, or RCK domains, which are found in certain K+ channels and control their gating. However, fundamental questions on whether TrkH is an ion channel and how it is regulated by TrkA remain unresolved. Here we show single-channel activity of TrkH that is upregulated by ATP via TrkA. We report two structures of the tetrameric TrkA ring, one in complex with TrkH and one in isolation, in which the ring assumes two dramatically different conformations. These results suggest a mechanism for how ATP increases TrkH activity by inducing conformational changes in TrkA.

Cao, Yu; Pan, Yaping; Huang, Hua; Jin, Xiangshu; Levin, Elena J.; Kloss, Brian; Zhou, Ming

2013-01-01

283

Integration of thermal and osmotic regulation of water homeostasis: the role of TRPV channels.  

PubMed

Maintenance of body water homeostasis is critical for preventing hyperthermia, because evaporative cooling is the most efficient means of dissipating excess body heat. Water homeostasis is achieved by regulation of water intake and water loss by the kidneys. The former is achieved by sensations of thirst that motivate water acquisition, whereas the latter is regulated by the antidiuretic action of vasopressin. Vasopressin secretion and thirst are stimulated by increases in the osmolality of the extracellular fluid as well as decreases in blood pressure and/or blood volume, signals that are precipitated by water depletion associated with the excess evaporative water loss required to prevent hyperthermia. In addition, they are stimulated by increases in body temperature. The sites and molecular mechanisms involved in integrating thermal and osmotic regulation of thirst and vasopressin secretion are reviewed here with a focus on the role of the thermal and mechanosensitive transient receptor potential-vanilloid (TRPV) family of ion channels. PMID:23883678

Sladek, Celia D; Johnson, Alan Kim

2013-07-24

284

Tetrameric assembly of CHIP28 water channels in liposomes and cell membranes: a freeze-fracture study  

PubMed Central

Channel forming integral protein of 28 kD (CHIP28) functions as a water channel in erythrocytes, kidney proximal tubule and thin descending limb of Henle. CHIP28 morphology was examined by freeze-fracture EM in proteoliposomes reconstituted with purified CHIP28, CHO cells stably transfected with CHIP28k cDNA, and rat kidney tubules. Liposomes reconstituted with HPLC-purified CHIP28 from human erythrocytes had a high osmotic water permeability (Pf0.04 cm/s) that was inhibited by HgCl2. Freeze-fracture replicas showed a fairly uniform set of intramembrane particles (IMPs); no IMPs were observed in liposomes without incorporated protein. By rotary shadowing, the IMPs had a diameter of 8.5 +/- 1.3 nm (mean +/- SD); many IMPs consisted of a distinct arrangement of four smaller subunits surrounding a central depression. IMPs of similar size and appearance were seen on the P-face of plasma membranes from CHIP28k-transfected (but not mock-transfected) CHO cells, rat thin descending limb (TDL) of Henle, and S3 segment of proximal straight tubules. A distinctive network of complementary IMP imprints was observed on the E-face of CHIP28-containing plasma membranes. The densities of IMPs in the size range of CHIP28 IMPs, determined by non-linear regression, were (in IMPs/microns 2): 2,494 in CHO cells, 5,785 in TDL, and 1,928 in proximal straight tubules; predicted Pf, based on the CHIP28 single channel water permeability of 3.6 x 10(-14) cm3/S (10 degrees C), was in good agreement with measured Pf of 0.027 cm/S, 0.075 cm/S, and 0.031 cm/S, respectively, in these cell types. Assuming that each CHIP28 monomer is a right cylindrical pore of length 5 nm and density 1.3 g/cm3, the monomer diameter would be 3.2 nm; a symmetrical arrangement of four cylinders would have a greatest diameter of 7.2 nm, which after correction for the thickness of platinum deposit, is similar to the measured IMP diameter of approximately 8.5 nm. These results provide a morphological signature for CHIP28 water channels and evidence for a tetrameric assembly of CHIP28 monomers in reconstituted proteoliposomes and cell membranes.

1993-01-01

285

Effect of channel catfish stocking rate on yield and water quality in an intensive, mixed suspended-growth production system  

Technology Transfer Automated Retrieval System (TEKTRAN)

This study was conducted to determine the effect of channel catfish (Ictalurus punctatus) stocking rate on yield and water quality in a mixed suspended-growth production system (bio-floc) with zero water exchange. Channel catfish (National Warmwater Aquaculture Center 103 strain; average weight = 13...

286

Water table and overbank flow frequency changes due to suburbanization-induced channel incision, Virginia Coastal Plain, USA  

Microsoft Academic Search

Channel incision is a widely observed response to increased flow in urbanized watersheds, but the effects of channel lowering on riparian water tables is not well documented. In a rapidly incising suburban stream in the Virginia Coastal Plain, we hypothesize that incision has lowered floodplain water tables and decreased the overbank flow frequency, and suggest these changes impact vegetation distribution

G. Hancock; N. Mattell; E. Christianson; J. Wacksman

2004-01-01

287

Computational Analysis of the Soluble Form of the Intracellular Chloride Ion Channel Protein CLIC1  

PubMed Central

The chloride intracellular channel (CLIC) family of proteins has the remarkable property of maintaining both a soluble form and an integral membrane form acting as an ion channel. The soluble form is structurally related to the glutathione-S-transferase family, and CLIC can covalently bind glutathione via an active site cysteine. We report approximately 0.6??s of molecular dynamics simulations, encompassing the three possible ligand-bound states of CLIC1, using the structure of GSH-bound human CLIC1. Noncovalently bound GSH was rapidly released from the protein, whereas the covalently ligand-bound protein remained close to the starting structure over 0.25??s of simulation. In the unliganded state, conformational changes in the vicinity of the glutathione-binding site resulted in reduced reactivity of the active site thiol. Elastic network analysis indicated that the changes in the unliganded state are intrinsic to the protein architecture and likely represent functional transitions. Overall, our results are consistent with a model of CLIC function in which covalent binding of glutathione does not occur spontaneously but requires interaction with another protein to stabilise the GSH binding site and/or transfer of the ligand. The results do not indicate how CLIC1 undergoes a radical conformational change to form a transmembrane chloride channel but further elucidate the mechanism by which CLICs are redox controlled.

Jones, Peter M.; Curmi, Paul M. G.; Valenzuela, Stella M.; George, Anthony M.

2013-01-01

288

Small Heat Shock Protein ?A-crystallin Regulates Epithelial Sodium Channel Expression*  

PubMed Central

Integral membrane proteins are synthesized on the cytoplasmic face of the endoplasmic reticulum (ER). After being translocated or inserted into the ER, they fold and undergo post-translational modifications. Within the ER, proteins are also subjected to quality control checkpoints, during which misfolded proteins may be degraded by proteasomes via a process known as ER-associated degradation. Molecular chaperones, including the small heat shock protein ?A-crystallin, have recently been shown to play a role in this process. We have now found that ?A-crystallin is expressed in cultured mouse collecting duct cells, where apical Na+ transport is mediated by epithelial Na+ channels (ENaC). ENaC-mediated Na+ currents in Xenopus oocytes were reduced by co-expression of ?A-crystallin. This reduction in ENaC activity reflected a decrease in the number of channels expressed at the cell surface. Furthermore, we observed that the rate of ENaC delivery to the cell surface of Xenopus oocytes was significantly reduced by co-expression of ?A-crystallin, whereas the rate of channel retrieval remained unchanged. We also observed that ?A-crystallin and ENaC co-immunoprecipitate. These data are consistent with the hypothesis that small heat shock proteins recognize ENaC subunits at ER quality control checkpoints and can target ENaC subunits for ER-associated degradation.

Kashlan, Ossama B.; Mueller, Gunhild M.; Qamar, Mohammad Z.; Poland, Paul A.; Ahner, Annette; Rubenstein, Ronald C.; Hughey, Rebecca P.; Brodsky, Jeffrey L.; Kleyman, Thomas R.

2008-01-01

289

Expression of the AQP-1 water channel in normal human tissues: a semiquantitative study using tissue microarray technology.  

PubMed

Aquaporin water channels are a family of membrane proteins that facilitate water movement across biological membranes. Aquaporin-1 (AQP-1) has been found to be important in osmotic water movement across cell membranes of epithelial and endothelial barriers. However, the distribution of AQP-1 in many normal human tissues is still unknown. The aim of this study was to use immunohistochemistry and semiquantitative histomorphometric analysis to determine the tissue distribution and relative expression of AQP-1 in normal human tissues using tissue microarray (TMA) technology. The normal human TMAs employed in this study included cardiovascular, respiratory, gastrointestinal, hepatic and pancreatobiliary, oral, salivary, nasal, mammary, fetal, endocrine, genital tract, central and peripheral nervous systems, urinary tract, skin, cartilage, and other soft connective tissues. Immunohistochemistry and semiquantitative histomorphometric analysis confirmed the presence of AQP-1 in endothelial barriers of almost all tissues and in many epithelial barriers. AQP-1 was highly expressed in the renal cortex, choroid plexus, and pancreatic ducts. AQP-1 expression levels were surprisingly high in the anus, gallbladder, and liver; moderate expression was also detected in the hippocampus and ependymal cells of the central nervous system. This is the first report of AQP-1 protein distribution in normal human TMAs. These findings confirm the presence of AQP-1 in human endothelia and selected water-transporting epithelia and several new locations, including mammary epithelium, articular chondrocytes, synoviocytes, and synovial microvessels where AQP-1 may be involved in milk production, chondrocyte volume regulation, synovial fluid secretion, and homeostasis, respectively. PMID:14592814

Mobasheri, A; Marples, D

2003-10-30

290

Hydrogen-Bonding Dynamics between Adjacent Blades in G-Protein ?-Subunit Regulates GIRK Channel Activation  

PubMed Central

Functionally critical domains in the ??-subunits of the G-protein (G??) do not undergo large structural rearrangements upon binding to other proteins. Here we show that a region containing Ser67 and Asp323 of G?? is a critical determinant of G-protein-gated inwardly rectifying K+ (GIRK) channel activation and undergoes only small structural changes upon mutation of these residues. Using an interactive experimental and computational approach, we show that mutants that form a hydrogen-bond between positions 67 and 323 do not activate a GIRK channel. We also show that in the absence of hydrogen-bonding between these positions, other factors, such as the displacement of the crucial G? residues Pro60 and Phe61, can impair G??-mediated GIRK channel activation. Our results imply that the dynamic nature of the hydrogen-bonding pattern in the wild-type serves an important functional role that regulates GIRK channel activation by G?? and that subtle changes in the flexibility of critical domains could have substantial functional consequences. Our results further strengthen the notion that the dynamic regulation of multiple interactions between G?? and effectors provides for a complex regulatory process in cellular functions.

Mirshahi, Tooraj; Logothetis, Diomedes E.; Rosenhouse-Dantsker, Avia

2006-01-01

291

The small envelope protein of porcine reproductive and respiratory syndrome virus possesses ion channel protein-like properties  

SciTech Connect

The small envelope (E) protein of porcine reproductive and respiratory syndrome virus (PRRSV) is a hydrophobic 73 amino acid protein encoded in the internal open reading frame (ORF) of the bicistronic mRNA2. As a first step towards understanding the biological role of E protein during PRRSV replication, E gene expression was blocked in a full-length infectious clone by mutating the ATG translational initiation to GTG, such that the full-length mutant genomic clone was unable to synthesize the E protein. DNA transfection of PRRSV-susceptible cells with the E gene knocked-out genomic clone showed the absence of virus infectivity. P129-{delta}E-transfected cells however produced virion particles in the culture supernatant, and these particles contained viral genomic RNA, demonstrating that the E protein is essential for PRRSV infection but dispensable for virion assembly. Electron microscopy suggests that the P129-{delta}E virions assembled in the absence of E had a similar appearance to the wild-type particles. Strand-specific RT-PCR demonstrated that the E protein-negative, non-infectious P129-{delta}E virus particles were able to enter cells but further steps of replication were interrupted. The entry of PRRSV has been suggested to be via receptor-mediated endocytosis, and lysomotropic basic compounds and known ion-channel blocking agents both inhibited PRRSV replication effectively during the uncoating process. The expression of E protein in Escherichia coli-mediated cell growth arrests and increased the membrane permeability. Cross-linking experiments in cells infected with PRRSV or transfected with E gene showed that the E protein was able to form homo-oligomers. Taken together, our data suggest that the PRRSV E protein is likely an ion-channel protein embedded in the viral envelope and facilitates uncoating of virus and release of the genome in the cytoplasm.

Lee, Changhee [Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, N1G 2W1 (Canada); Yoo, Dongwan [Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, N1G 2W1 (Canada)]. E-mail: dyoo@uoguelph.ca

2006-11-10

292

Helix-Coil Kinetics of Individual Polyadenylic Acid Molecules in a Protein Channel  

NASA Astrophysics Data System (ADS)

Helix-coil transition kinetics of polyadenylic acid [poly(A)] inside a small protein channel is investigated for the first time, at the single molecule level. The confinement of a RNA molecule inside the channel slows its kinetics by nearly 3 orders of magnitude as compared to bulk measurements of free poly(A). These findings are related to the interaction energy of the RNA structure with the interior of the pore, explained by a simple two-state model. These results shed light on the way intermolecular interactions alter nucleic acid kinetics.

Lin, Jianxun; Kolomeisky, Anatoly; Meller, Amit

2010-04-01

293

Differential modulation of Cav2.1 channels by calmodulin and Ca2+-binding protein 1  

Microsoft Academic Search

Cav2.1 channels, which mediate P\\/Q-type Ca2+ currents, undergo Ca2+\\/calmodulin (CaM)-dependent inactivation and facilitation that can significantly alter synaptic efficacy. Here we report that the neuronal Ca2+-binding protein 1 (CaBP1) modulates Cav2.1 channels in a manner that is markedly different from modulation by CaM. CaBP1 enhances inactivation, causes a depolarizing shift in the voltage dependence of activation, and does not support

Amy Lee; Ruth E. Westenbroek; Françoise Haeseleer; Krzysztof Palczewski; Todd Scheuer; William A. Catterall

2002-01-01

294

Visualizing water molecules in transmembrane proteins using radiolytic labeling methods†  

PubMed Central

Essential to cells and their organelles, water is both shuttled to where it is needed and trapped within cellular compartments and structures. Moreover, ordered waters within protein structures often co-localize with strategically placed polar or charged groups critical for protein function. Yet it is unclear if these ordered water molecules provide structural stabilization, mediate conformational changes in signaling, neutralize charged residues, or carry out a combination of all these functions. Structures of many integral membrane proteins, including G protein-coupled receptors (GPCRs), reveal the presence of ordered water molecules that may act like prosthetic groups in a manner quite unlike bulk water. Identification of ‘ordered’ waters within a crystalline protein structure requires sufficient occupancy of water to enable its detection in the protein's X-ray diffraction pattern and thus the observed waters likely represent a subset of tightly-bound functional waters. In this review, we highlight recent studies that suggest the structures of ordered waters within GPCRs are as conserved (and thus as important) as conserved side chains. In addition, methods of radiolysis, coupled to structural mass spectrometry (protein footprinting), reveal dynamic changes in water structure that mediate transmembrane signaling. The idea of water as a prosthetic group mediating chemical reaction dynamics is not new in fields such as catalysis. However, the concept of water as a mediator of conformational dynamics in signaling is just emerging, owing to advances in both crystallographic structure determination and new methods of protein footprinting. Although oil and water do not mix, understanding the roles of water is essential to understanding the function of membrane proteins.

Orban, Tivadar; Gupta, Sayan; Palczewski, Krzysztof; Chance, Mark R.

2010-01-01

295

Visualizing Water Molecules in Transmembrane Proteins Using Radiolytic Labeling Methods  

SciTech Connect

Essential to cells and their organelles, water is both shuttled to where it is needed and trapped within cellular compartments and structures. Moreover, ordered waters within protein structures often colocalize with strategically placed polar or charged groups critical for protein function, yet it is unclear if these ordered water molecules provide structural stabilization, mediate conformational changes in signaling, neutralize charged residues, or carry out a combination of all these functions. Structures of many integral membrane proteins, including G protein-coupled receptors (GPCRs), reveal the presence of ordered water molecules that may act like prosthetic groups in a manner quite unlike bulk water. Identification of 'ordered' waters within a crystalline protein structure requires sufficient occupancy of water to enable its detection in the protein's X-ray diffraction pattern, and thus, the observed waters likely represent a subset of tightly bound functional waters. In this review, we highlight recent studies that suggest the structures of ordered waters within GPCRs are as conserved (and thus as important) as conserved side chains. In addition, methods of radiolysis, coupled to structural mass spectrometry (protein footprinting), reveal dynamic changes in water structure that mediate transmembrane signaling. The idea of water as a prosthetic group mediating chemical reaction dynamics is not new in fields such as catalysis. However, the concept of water as a mediator of conformational dynamics in signaling is just emerging, because of advances in both crystallographic structure determination and new methods of protein footprinting. Although oil and water do not mix, understanding the roles of water is essential to understanding the function of membrane proteins.

Orban, T.; Gupta, S; Palczewski, K; Chance, M

2010-01-01

296

Constitutively active G-protein-gated inwardly rectifying K+ channels in dendrites of hippocampal CA1 pyramidal neurons.  

PubMed

A diversity of ion channels contributes to the active properties of neuronal dendrites. From the apical dendrites of hippocampal CA1 pyramidal neurons, we recorded inwardly rectifying K+ channels with a single-channel conductance of 33 pS. The inwardly rectifying K+ channels were constitutively active at the resting membrane potential. The amount of constitutive channel activity was significantly larger in the apical dendrites than in the soma. Activities of these inwardly rectifying K+ channels were inhibited by Ba2+ (200 microM) and tertiapin (10 nM), both of which are believed to block G-protein-coupled inwardly rectifying K+ (GIRK) channels. Intracellularly applied GTPgammaS (20 microM) during dual dendritic recordings significantly increased constitutive channel activity. Baclofen (20 microM), an agonist for the G-protein-coupled GABA(B) receptor, also significantly increased the level of channel activity. Therefore, these channels are GIRK channels, which are constitutively active at rest in the apical dendrites of CA1 pyramidal neurons and can be further activated via G-protein-coupled neurotransmitter receptors. PMID:15829630

Chen, Xixi; Johnston, Daniel

2005-04-13

297

Use of optical biosensors to detect modulation of Slack potassium channels by G protein-coupled receptors.  

PubMed

Ion channels control the electrical properties of neurons and other excitable cell types by selectively allowing ion to flow through the plasma membrane. To regulate neuronal excitability, the biophysical properties of ion channels are modified by signaling proteins and molecules, which often bind to the channels themselves to form a heteromeric channel complex. Traditional assays examining the interaction between channels and regulatory proteins generally provide little information on the time-course of interactions in living cells. We have now used a novel label-free technology to detect changes in the distribution of mass close to the plasma membrane following modulation of potassium channels by G protein-coupled receptors (GPCRs). This technology uses optical sensors embedded in microplates to detect changes in the refractive index at the surface of cells. Although the activation of GPCRs has been studied with this system, protein-protein interactions due to modulation of ion channels have not yet been characterized. Here we present data that the characteristic pattern of mass distribution following GPCR activation is significantly modified by the presence of a sodium-activated potassium channel, Slack-B, a channel that is known to be potently modulated by activation of these receptors. PMID:19640220

Fleming, Matthew R; Kaczmarek, Leonard K

2009-01-01

298

The Structure and Transport of Water and Hydrated Ions Within Hydrophobic, Nanoscale Channels  

SciTech Connect

The purpose of this project includes an experimental and modeling investigation into water and hydrated ion structure and transport at nanomaterials interfaces. This is a topic relevant to understanding the function of many biological systems such as aquaporins that efficiently shuttle water and ion channels that permit selective transport of specific ions across cell membranes. Carbon nanotubes (CNT) are model nanoscale, hydrophobic channels that can be functionalized, making them artificial analogs for these biological channels. This project investigates the microscopic properties of water such as water density distributions and dynamics within CNTs using Nuclear Magnetic Resonance (NMR) and the structure of hydrated ions at CNT interfaces via X-ray Absorption Spectroscopy (XAS). Another component of this work is molecular simulation, which can predict experimental measurables such as the proton relaxation times, chemical shifts, and can compute the electronic structure of CNTs. Some of the fundamental questions this work is addressing are: (1) what is the length scale below which nanoscale effects such as molecular ordering become important, (2) is there a relationship between molecular ordering and transport?, and (3) how do ions interact with CNT interfaces? These are questions of interest to the scientific community, but they also impact the future generation of sensors, filters, and other devices that operate on the nanometer length scale. To enable some of the proposed applications of CNTs as ion filtration media and electrolytic supercapacitors, a detailed knowledge of water and ion structure at CNT interfaces is critical.

Holt, J K; Herberg, J L; Wu, Y; Schwegler, E; Mehta, A

2009-06-15

299

Groundwater-surface water interaction in the riparian zone of an incised channel, Walnut Creek, Iowa  

USGS Publications Warehouse

Riparian zones of many incised channels in agricultural regions are cropped to the channel edge leaving them unvegetated for large portions of the year. In this study we evaluated surface and groundwater interaction in the riparian zone of an incised stream during a spring high flow period using detailed stream stage and hydraulic head data from six wells, and water quality sampling to determine whether the riparian zone can be a source of nitrate pollution to streams. Study results indicated that bank storage of stream water from Walnut Creek during a large storm water runoff event was limited to a narrow 1.6 m zone immediately adjacent to the channel. Nitrate concentrations in riparian groundwater were highest near the incised stream where the unsaturated zone was thickest. Nitrate and dissolved oxygen concentrations and nitrate-chloride ratios increased during a spring recharge period then decreased in the latter portion of the study. We used MODFLOW and MT3DMS to evaluate dilution and denitrification processes that would contribute to decreasing nitrate concentrations in riparian groundwater over time. MT3DMS model simulations were improved with a denitrification rate of 0.02 1/d assigned to the floodplain sediments implying that denitrification plays an important role in reducing nitrate concentrations in groundwater. We conclude that riparian zones of incised channels can potentially be a source of nitrate to streams during spring recharge periods when the near-stream riparian zone is largely unvegetated. ?? 2005 Elsevier B.V. All rights reserved.

Schilling, K. E.; Li, Z.; Zhang, Y. -K.

2006-01-01

300

Ser123 Is Essential for the Water Channel Activity of McPIP2;1 from Mesembryanthemum crystallinum*  

PubMed Central

The increased expression of McPIP2;1 (MipC), a root-specific aquaporin (AQP) from Mesembryanthemum crystallinum, under salt stress has suggested a role for this AQP in the salt tolerance of the plant. However, whether McPIP2;1 transports water or another solute and how its activity is regulated are so far unknown. Therefore, wild type (wt) or mutated McPIP2;1 protein was expressed in Xenopus laevis oocytes. Then, the osmotic water permeability (Pf) of the oocytes membrane was assessed by hypotonic challenges. Selectivity of McPIP2;1 to water was determined by radiolabeled glycerol or urea uptake assays. Moreover, swelling and in vitro phosphorylation assays revealed that both water permeation and phosphorylation status of McPIP2;1 were significantly increased by the phosphorylation agonists okadaic acid (OA), phorbol myristate acetate (PMA), and 8-Br-cAMP, and markedly decreased by the inhibitory peptides PKI 14-22 and PKC 20-28, inhibitors of protein kinases A (PKA) and C (PKC), respectively. Substitution of Ser123 or both, Ser123 and Ser282, abolished the water channel activity of McPIP2;1 while substitution of Ser282 only partially inhibited it (51.9% inhibition). Despite lacking Ser123 and/or Ser282, the McPIP2;1 mutant forms were still phosphorylated in vitro, which suggests that phosphorylation may have a dual role on this AQP. Our results indicate that McPIP2;1 water permeability depends completely on Ser123 and is positively regulated by PKA- and PKC-mediated phosphorylation. Regulation of the phosphorylation status of McPIP2;1 may contribute to control water transport through root cells when the plant is subjected to high salinity conditions.

Amezcua-Romero, Julio C.; Pantoja, Omar; Vera-Estrella, Rosario

2010-01-01

301

Ser123 is essential for the water channel activity of McPIP2;1 from Mesembryanthemum crystallinum.  

PubMed

The increased expression of McPIP2;1 (MipC), a root-specific aquaporin (AQP) from Mesembryanthemum crystallinum, under salt stress has suggested a role for this AQP in the salt tolerance of the plant. However, whether McPIP2;1 transports water or another solute and how its activity is regulated are so far unknown. Therefore, wild type (wt) or mutated McPIP2;1 protein was expressed in Xenopus laevis oocytes. Then, the osmotic water permeability (P(f)) of the oocytes membrane was assessed by hypotonic challenges. Selectivity of McPIP2;1 to water was determined by radiolabeled glycerol or urea uptake assays. Moreover, swelling and in vitro phosphorylation assays revealed that both water permeation and phosphorylation status of McPIP2;1 were significantly increased by the phosphorylation agonists okadaic acid (OA), phorbol myristate acetate (PMA), and 8-Br-cAMP, and markedly decreased by the inhibitory peptides PKI 14-22 and PKC 20-28, inhibitors of protein kinases A (PKA) and C (PKC), respectively. Substitution of Ser(123) or both, Ser(123) and Ser(282), abolished the water channel activity of McPIP2;1 while substitution of Ser(282) only partially inhibited it (51.9% inhibition). Despite lacking Ser(123) and/or Ser(282), the McPIP2;1 mutant forms were still phosphorylated in vitro, which suggests that phosphorylation may have a dual role on this AQP. Our results indicate that McPIP2;1 water permeability depends completely on Ser(123) and is positively regulated by PKA- and PKC-mediated phosphorylation. Regulation of the phosphorylation status of McPIP2;1 may contribute to control water transport through root cells when the plant is subjected to high salinity conditions. PMID:20332086

Amezcua-Romero, Julio C; Pantoja, Omar; Vera-Estrella, Rosario

2010-03-23

302

Changes of calcium channel mRNA, protein and current in NG108-15 cells after cell differentiation.  

PubMed

Based on the characteristics of differentiated NG108-15 cells (cell membrane excitability, acetylcholine release, and activities of choline acetyltransferase and acetylcholinesterase), NG108-15 cells are extensively used to explore neuronal functions as a cholinergic cell line. In the present study, differentiation-induced alterations of voltage-gated Ca(2+) channel mRNA, protein, and current were investigated in the NG108-15 cells. Real-time PCR, Western blot, and whole-cell patch-clamp data showed that differentiation caused mRNA, protein, and ion current changes of all Ca(2+) channel subunits. However, the changes of mRNA, protein, and ion current are inconsistent in all Ca(2+) channel subunits. Especially, P/Q- and R-type Ca(2+) channel proteins do not form the functional P/Q- and R-type Ca(2+) channels even if the mRNA and protein of P/Q- and R-type Ca(2+) channels can be detected in NG108-15 cells. These results indicate that differentiation can modulate gene transcription, protein translation, and post-translation of the Ca(2+) channels to induce the alteration of the Ca(2+) ion currents in NG108-15 cells. From these data, we understand that combining real-time PCR, Western blot, and patch-clamp techniques can comprehensively unveil the modulation of the Ca(2+) channels. PMID:22627136

Liu, Jinxu; Tu, Huiyin; Zhang, Dongze; Li, Yu-Long

2012-05-22

303

Effect of channelization of Rio Puerto Nuevo on ground-water levels in the San Juan metropolitan area, Puerto Rico  

USGS Publications Warehouse

Channelization and concrete lining of the Rio Puerto Nuevo and its tributaries in the San Juan Metropolitan area has been proposed to control flooding in low lying areas adjacent to the stream. Concern about the effect of these channel modifications on the ground-water system prompted the U.S. Geological Survey in cooperation with the U.S. Army Corps of Engineers to conduct an investigation of surface-water and ground-water interactions in the Rio Puerto Nuevo basin in 1988. A principal objective of this investigation was to determine the potential effect of channelization of the Rio Puerto Nuevo on ground-water levels.

Padilla, Ingrid

1991-01-01

304

Protein arginine methyl transferases-3 and -5 increase cell surface expression of cardiac sodium channel.  

PubMed

The ?-subunit of the cardiac voltage-gated sodium channel (NaV1.5) plays a central role in cardiomyocyte excitability. We have recently reported that NaV1.5 is post-translationally modified by arginine methylation. Here, we aimed to identify the enzymes that methylate NaV1.5, and to describe the role of arginine methylation on NaV1.5 function. Our results show that protein arginine methyl transferase (PRMT)-3 and -5 methylate NaV1.5 in vitro, interact with NaV1.5 in human embryonic kidney (HEK) cells, and increase NaV1.5 current density by enhancing NaV1.5 cell surface expression. Our observations are the first evidence of regulation of a voltage-gated ion channel, including calcium, potassium, sodium and TRP channels, by arginine methylation. PMID:23912080

Beltran-Alvarez, Pedro; Espejo, Alexsandra; Schmauder, Ralf; Beltran, Carlos; Mrowka, Ralf; Linke, Thomas; Batlle, Montserrat; Pérez-Villa, Félix; Pérez, Guillermo J; Scornik, Fabiana S; Benndorf, Klaus; Pagans, Sara; Zimmer, Thomas; Brugada, Ramon

2013-07-31

305

Hypomyelination and increased activity of voltage-gated K+ channels in mice lacking protein tyrosine phosphatase ?  

PubMed Central

Protein tyrosine phosphatase epsilon (PTP?) is strongly expressed in the nervous system; however, little is known about its physiological role. We report that mice lacking PTP? exhibit hypomyelination of sciatic nerve axons at an early post-natal age. This occurs together with increased activity of delayed- rectifier, voltage-gated potassium (Kv) channels and with hyperphosphorylation of Kv1.5 and Kv2.1 Kv channel ?-subunits in sciatic nerve tissue and in primary Schwann cells. PTP? markedly reduces Kv1.5 or Kv2.1 current amplitudes in Xenopus oocytes. Kv2.1 associates with a substrate-trapping mutant of PTP?, and PTP? profoundly reduces Src- or Fyn-stimulated Kv2.1 currents and tyrosine phosphorylation in transfected HEK 293 cells. In all, PTP? antagonizes activation of Kv channels by tyrosine kinases in vivo, and affects Schwann cell function during a critical period of Schwann cell growth and myelination.

Peretz, A.; Gil-Henn, H.; Sobko, A.; Shinder, V.; Attali, B.; Elson, A.

2000-01-01

306

Molecular properties of neuronal G-protein-activated inwardly rectifying K+ channels.  

PubMed

Four cDNA-encoding G-activated inwardly rectifying K+ channels have been cloned recently (Kubo, Y., Reuveny, E., Slesinger, P. A., Jan, Y. N., and Jan, L. Y. (1993) Nature 364, 802-806; Lesage, F., Duprat, F., Fink, M., Guillemare, E., Coppola, T., Lazdunski, M., and Hugnot, J. P. (1994) FEBS Lett. 353, 37-42; Krapivinsky, G., Gordon, E. A., Wickman, K., Velimirovic, B., Krapivinsky, L., and Clapham, D. E. (1995) Nature 374, 135-141). We report the cloning of a mouse GIRK2 splice variant, noted mGIRK2A. Both channel proteins are functionally expressed in Xenopus oocytes upon injection of their cRNA, alone or in combination with the GIRK1 cRNA. Three GIRK channels, mGIRK1-3, are shown to be present in the brain. Colocalization in the same neurons of mGIRK1 and mGIRK2 supports the hypothesis that native channels are made by an heteromeric subunit assembly. GIRK3 channels have not been expressed successfully, even in the presence of the other types of subunits. However, GIRK3 chimeras with the amino- and carboxyl-terminal of GIRK2 are functionally expressed in the presence of GIRK1. The expressed mGIRK2 and mGIRK1, -2 currents are blocked by Ba2+ and Cs+ ions. They are not regulated by protein kinase A and protein kinase C. Channel activity runs down in inside-out excised patches, and ATP is required to prevent this rundown. Since the nonhydrolyzable ATP analog AMP-PCP is also active and since addition of kinases A and C as well as alkaline phosphatase does not modify the ATP effect, it is concluded that ATP hydrolysis is not required. An ATP binding process appears to be essential for maintaining a functional state of the neuronal inward rectifier K+ channel. A Na+ binding site on the cytoplasmic face of the membrane acts in synergy with the ATP binding site to stabilize channel activity. PMID:7499385

Lesage, F; Guillemare, E; Fink, M; Duprat, F; Heurteaux, C; Fosset, M; Romey, G; Barhanin, J; Lazdunski, M

1995-12-01

307

Circulation, Water Temperature, and Larval Settlement Over the Inner Continental Shelves of the Santa Barbara Channel, California  

Microsoft Academic Search

We use seven-year time series of wind stress, water velocity, and temperature in 15-18 m water depth to describe the circulation and water temperature over the inner continental shelves of the Channel Islands and California mainland in the Santa Barbara Basin. This area is strongly influenced by the California Current upwelling system. In turn, the water circulation in the Santa

M. R. Fewings; L. Washburn; C. Ohlmann; C. Blanchette; J. Caselle; C. Gotschalk

2008-01-01

308

Synergistic Activation of G Protein-gated Inwardly Rectifying Potassium Channels by the betagamma Subunits of G Proteins and Na+ and Mg2+ Ions  

Microsoft Academic Search

Native and recombinant G protein-gated inwardly rectifying potassium (GIRK) channels are directly activated by the bg subunits of GTP-binding (G) proteins. The presence of phosphatidylinositol-bis-phosphate (PIP 2 ) is required for G protein activation. Formation (via hydrolysis of ATP) of endogenous PIP 2 or application of exogenous PIP 2 increases the mean open time of GIRK channels and sensitizes them

Jérôme Petit-Jacques; Jin Liang Sui; Diomedes E. Logothetis

1999-01-01

309

Using Ion Channel-Forming Peptides to Quantify Protein-Ligand Interactions  

PubMed Central

This paper proposes a method for sensing affinity interactions by triggering disruption of self-assembly of ion channel-forming peptides in planar lipid bilayers. It shows that the binding of a derivative of alamethicin carrying a covalently attached sulfonamide ligand to carbonic anhydrase II (CA II) resulted in the inhibition of ion channel conductance through the bilayer. We propose that the binding of the bulky CA II protein (MW ~30 kD) to the ion channel-forming peptides (MW ~2.5 kD) either reduced the tendency of these peptides to self-assemble into a pore, or extracted them from the bilayer altogether. In both outcomes, the interactions between the protein and the ligand lead to a disruption of self-assembled pores. Addition of a competitive inhibitor – 4-carboxybenzenesulfonamide – to the solution released CA II from the alamethicin-sulfonamide conjugate and restored the current flow across the bilayer by allowing reassembly of the ion channels in the bilayer. Time-averaged recordings of the current over discrete time intervals made it possible to quantify this monovalent ligand binding interaction. This method gave a dissociation constant of ~2 µM for the binding of CA II to alamethicin-sulfonamide in the bilayer recording chamber: this value is consistent with a value obtained independently with CA II and a related sulfonamide derivative by isothermal titration calorimetry.

Mayer, Michael; Semetey, Vincent; Gitlin, Irina; Yang, Jerry; Whitesides, George M.

2008-01-01

310

Inhibition of Ca2+ Channels and Adrenal Catecholamine Release by G Protein Coupled Receptors  

PubMed Central

Catecholamines and other transmitters released from adrenal chromaffin cells play central roles in the “fight-or-flight” response and exert profound effects on cardiovascular, endocrine, immune, and nervous system function. As such, precise regulation of chromaffin cell exocytosis is key to maintaining normal physiological function and appropriate responsiveness to acute stress. Chromaffin cells express a number of different G protein coupled receptors (GPCRs) that sense the local environment and orchestrate this precise control of transmitter release. The primary trigger for catecholamine release is Ca2+ entry through voltage-gated Ca2+ channels, so it makes sense that these channels are subject to complex regulation by GPCRs. In particular G protein ?? heterodimers (G??) bind to and inhibit Ca2+ channels. Here I review the mechanisms by which GPCRs inhibit Ca2+ channels in chromaffin cells and how this might be altered by cellular context. This is related to the potent autocrine inhibition of Ca2+ entry and transmitter release seen in chromaffin cells. Recent data that implicate an additional inhibitory target of G?? on the exocytotic machinery and how this might fine tune neuroendocrine secretion are also discussed.

2011-01-01

311

Mutation of a putative S-nitrosylation site of TRPV4 protein facilitates the channel activates  

PubMed Central

The transient receptor potential vanilloid 4 (TRPV4) cation channel, a member of the TRP vanilloid subfamily, is expressed in a broad range of tissues. Nitric oxide (NO) as a gaseous signal mediator shows a variety of important biological effects. In many instances, NO has been shown to exhibit its activities via a protein S-nitrosylation mechanism in order to regulate its protein functions. With functional assays via site-directed mutagenesis, we demonstrate herein that NO induces the S-nitrosylation of TRPV4 Ca2+ channel on the Cys853 residue, and the S-nitrosylation of Cys853 reduced its channel sensitivity to 4-? phorbol 12,13-didecanoate and the interaction between TRPV4 and calmodulin. A patch clamp experiment and Ca2+ image analysis show that the S-nitrosylation of Cys853 modulates the TRPV4 channel as an inhibitor. Thus, our data suggest a novel regulatory mechanism of TRPV4 via NO-mediated S-nitrosylation on its Cys853 residue.

Lee, Eun Jeoung; Shin, Sung Hwa; Hyun, Sunghee; Chun, Jaesun; Kang, Sang Sun

2011-01-01

312

Polyester modification of the mammalian TRPM8 channel protein: implications for structure and function.  

PubMed

The TRPM8 ion channel is expressed in sensory neurons and is responsible for sensing environmental cues, such as cold temperatures and chemical compounds, including menthol and icilin. The channel functional activity is regulated by various physical and chemical factors and is likely to be preconditioned by its molecular composition. Our studies indicate that the TRPM8 channel forms a structural-functional complex with the polyester poly-(R)-3-hydroxybutyrate (PHB). We identified by mass spectrometry a number of PHB-modified peptides in the N terminus of the TRPM8 protein and in its extracellular S3-S4 linker. Removal of PHB by enzymatic hydrolysis and site-directed mutagenesis of both the serine residues that serve as covalent anchors for PHB and adjacent hydrophobic residues that interact with the methyl groups of the polymer resulted in significant inhibition of TRPM8 channel activity. We conclude that the TRPM8 channel undergoes posttranslational modification by PHB and that this modification is required for its normal function. PMID:23850286

Cao, Chike; Yudin, Yevgen; Bikard, Yann; Chen, Wei; Liu, Tong; Li, Hong; Jendrossek, Dieter; Cohen, Alejandro; Pavlov, Evgeny; Rohacs, Tibor; Zakharian, Eleonora

2013-07-11

313

Structure of a complex of the ATPase SecA and the protein-translocation channel  

SciTech Connect

Most proteins are secreted from bacteria by the interaction of the cytoplasmic SecA ATPase with a membrane channel, formed by the heterotrimeric SecY complex. Here we report the crystal structure of SecA bound to the SecY complex, with a maximum resolution of 4.5 {angstrom}, obtained for components from Thermotoga maritima. One copy of SecA in an intermediate state of ATP hydrolysis is bound to one molecule of the SecY complex. Both partners undergo important conformational changes on interaction. The polypeptide-cross-linking domain of SecA makes a large conformational change that could capture the translocation substrate in a 'clamp'. Polypeptide movement through the SecY channel could be achieved by the motion of a 'two-helix finger' of SecA inside the cytoplasmic funnel of SecY, and by the coordinated tightening and widening of SecA's clamp above the SecY pore. SecA binding generates a 'window' at the lateral gate of the SecY channel and it displaces the plug domain, preparing the channel for signal sequence binding and channel opening.

Zimmer, Jochen; Nam, Yunsun; Rapoport, Tom A. (Harvard-MED)

2009-01-23

314

Carbon nanotube sensors integrated inside a microfluidic channel for water quality monitoring  

NASA Astrophysics Data System (ADS)

Single-walled carbon nanotubes (SWNTs) with their unique electrical properties and large surface area are remarkable materials for detecting low concentration of toxic and hazardous chemicals (both from the gaseous and liquid phases). Ionic adsorbates in water will attach on to SWNTs and drastically alter their electrical properties. Several SWNTs based pH and chemical sensors have been demonstrated. However, most of them require external components to test and analyze the response of SWNTs to ions inside the liquid samples. Here, we report a water quality monitoring sensor composed of SWNTs integrated inside microfluidic channels and on-chip testing components with a wireless transmission board. To detect multiple analytes in water requires the functionalization of SWNTs with different chemistries. In addition, microfluidic channels are used to guide liquid samples to individual nanotube sensors in an efficient manner. Furthermore, the microfluidic system enables sample mixing and separation before testing. To realize the nanosensors, first microelectrodes were fabricated on an oxidized silicon substrate. Next, PDMS micro channels were fabricated and bonded on the substrate. These channels can be incorporated with a microfluidic system which can be designed to manipulate different analytes for specific molecule detection. Low temperature, solution based Dielectrophoretic (DEP) assembly was conducted inside this microfluidic system which successfully bridged SWNTs between the microelectrodes. The SWNTs sensors were next characterized with different pH buffer solutions. The resistance of SWNTs had a linearly increase as the pH values ranged from 5 to 8. The nanosensor incorporated within the microfluidic system is a versatile platform and can be utilized to detect numerous water pollutants, including toxic organics and microorganisms down to low concentrations. On-chip processing and wireless transmission enables the realization of a full autonomous system for real time monitoring of water quality.

Liu, Yu; Li, Xinghui; Dokmeci, Mehmet R.; Wang, Ming L.

2011-03-01

315

A ubiquitous 64-kDa protein is a component of a chloride channel of plasma and intracellular membranes.  

PubMed Central

Chloride channels are present in the plasma and intracellular membranes of most cells. Previously, using the ligand indanyloxyacetic acid (IAA), we purified four major proteins from bovine kidney cortex membrane vesicles. These proteins gave rise to chloride channel activity when reconstituted into phospholipid vesicles. Two of these proteins (97 and 27 kDa) were found to be drug-binding proteins by N-terminal sequence analysis. Antibodies raised to the 64-kDa protein stained only this protein on immunoblots, and only this protein was present after purification on an immunoaffinity column. In addition, these same antibodies were able to deplete IAA-94 inhibitable chloride channel activity from solubilized kidney membranes. Of fractions obtained from the gel filtration of solubilized kidney membranes, only those containing this 64-kDa protein exhibited measurable chloride channel activity. Immunoblots of a variety of species and cell types, both epithelial and nonepithelial, revealed that this protein is ubiquitous and highly conserved. Immunocytochemistry in CFPAC-1 cells revealed staining for this protein on the apical plasma membrane and in the membranes of intracellular organelles. These results demonstrate that the integral membrane protein p64 is a component of chloride channels present in both epithelial plasma membrane and the membranes of intracellular organelles. Images

Redhead, C R; Edelman, A E; Brown, D; Landry, D W; al-Awqati, Q

1992-01-01

316

Differential Occurrence of Reluctant Openings in G-Protein-Inhibited N- and P/Q-Type Calcium Channels  

PubMed Central

Voltage-dependent inhibition of N- and P/Q-type calcium channels by G proteins is crucial for presynaptic inhibition of neurotransmitter release, and may contribute importantly to short-term synaptic plasticity. Such calcium-channel modulation could thereby impact significantly the neuro-computational repertoire of neural networks. The differential modulation of N and P/Q channels could even further enrich their impact upon synaptic tuning. Here, we performed in-depth comparison of the G-protein inhibition of recombinant N and P/Q channels, expressed in HEK 293 cells with the m2 muscarinic receptor. While both channel types display classic features of G-protein modulation (kinetic slowing of activation, prepulse facilitation, and voltage dependence of inhibition), we confirmed previously reported quantitative differences, with N channels displaying stronger inhibition and greater relief of inhibition by prepulses. A more fundamental, qualitative difference in the modulation of these two channels was revealed by a modified tail-activation paradigm, as well as by a novel “slope” analysis method comparing time courses of slow activation and prepulse facilitation. The stark contrast in modulatory behavior can be understood within the context of the “willing–reluctant” model, in which binding of G-protein ?? subunits to channels induces a reluctant mode of gating, where stronger depolarization is required for opening. Our experiments suggest that only N channels could be opened in the reluctant mode, at voltages normally spanned by neuronal action potentials. By contrast, P/Q channels appear to remain closed, especially over these physiological voltages. Further, the differential occurrence of reluctant openings is not explained by differences in the rate of G-protein unbinding from the two channels. These two scenarios predict very different effects of G-protein inhibition on the waveform of Ca2+ entry during action potentials, with potentially important consequences for the timing and efficacy of synaptic transmission.

Colecraft, Henry M.; Patil, Parag G.; Yue, David T.

2000-01-01

317

Increased Asynchronous Release and Aberrant Calcium Channel Activation in Amyloid Precursor Protein Deficient Neuromuscular Synapses  

PubMed Central

Despite the critical roles of the amyloid precursor protein (APP) in Alzheimer's disease pathogenesis, its physiological function remains poorly established. Our previous studies implicated a structural and functional activity of the APP family of proteins in the developing neuromuscular junction (NMJ). Here we performed comprehensive analyses of neurotransmission in mature neuromuscular synapse of APP deficient mice. We found that APP deletion led to reduced paired-pulse facilitation and increased depression of synaptic transmission with repetitive stimulation. Readily releasable pool size and total releasable vesicles were not affected, but probability of release was significantly increased. Strikingly, the amount of asynchronous release, a measure sensitive to presynaptic calcium concentration, was dramatically increased, and pharmacological studies revealed that it was attributed to aberrant activation of N- and L-type Ca2+ channels. We propose that APP modulates synaptic transmission at the NMJ by ensuring proper Ca2+ channel function.

Yang, Li; Wang, Baiping; Long, Cheng; Wu, Gangyi; Zheng, Hui

2007-01-01

318

Reaction enthalpies along the two channels of geminate electron recombination in liquid-to-supercritical water  

NASA Astrophysics Data System (ADS)

Ionizing radiation or UV light produces electrons and H2O+ ions in water. These species transform into hydrated electron, e-aq, hydrated H3O+ ion, and ·OH radical in each other's neighborhood much faster than any forthcoming chemical transformation. Part of the electrons escapes their geminate partners. There exists two possible paths for the remaining fraction to react: H3O++e-aq=H3O· [channel (A)] and ·OH+e-aq=OH- [channel (B)]. We devised two thermodynamic cycles for the computation of the reaction enthalpies of both channels. Channel (A) was found to be endothermic with an enthalpy of 3.61 eV at room temperature. The enthalpy is seen to be almost constant up to 500 K, to increase at 600 K and to drop abruptly around 650 K, i.e. in the region where the dielectric constant is below 20. Channel (B) was found to be exothermic with an enthalpy of -2.33 eV at room temperature. It is becoming gradually less exothermic with increasing temperature the variation becoming fast around 650 K. The tendency of these thermochemical results parallel with recent kinetic calculations by Torres-Alacan et al. (J. Torres-Alacan, S. Kratz, P. Vöhringer, 2011. Phys. Chem. Chem. Phys. 13, 20806-20819)

Schiller, Robert; Horváth, Ákos

2013-11-01

319

The roles of G proteins in the activation of TRPC4 and TRPC5 transient receptor potential channels.  

PubMed

TRPC4 and TRPC5 channels are important regulators of electrical excitability in both gastrointestinal myocytes and neurons. Much is known regarding the assembly and function of these channels including TRPC1 as a homotetramer or a heteromultimer and the roles that their interacting proteins play in controlling these events. Further, they are one of the best-studied targets of G protein-coupled receptors and growth factors in general and G?q protein coupled receptor or epidermal growth factor in particular. However, our understanding of the roles of G?i/o proteins on TRPC4/5 channels is still rudimentary. We discuss potential roles for G?i/o proteins in channel activation in addition to their known role in cellular signaling. PMID:22878724

Kim, Hana; Kim, Jinsung; Jeon, Jae-Pyo; Myeong, Jongyun; Wie, Jinhong; Hong, Chansik; Kim, Hyun Jin; Jeon, Ju-Hong; So, Insuk

2012-08-10

320

The roles of G proteins in the activation of TRPC4 and TRPC5 transient receptor potential channels  

PubMed Central

TRPC4 and TRPC5 channels are important regulators of electrical excitability in both gastrointestinal myocytes and neurons. Much is known regarding the assembly and function of these channels including TRPC1 as a homotetramer or a heteromultimer and the roles that their interacting proteins play in controlling these events. Further, they are one of the best-studied targets of G protein-coupled receptors and growth factors in general and G?q protein coupled receptor or epidermal growth factor in particular. However, our understanding of the roles of G?i/o proteins on TRPC4/5 channels is still rudimentary. We discuss potential roles for G?i/o proteins in channel activation in addition to their known role in cellular signaling.

Kim, Hana; Kim, Jinsung; Jeon, Jae-Pyo; Myeong, Jongyun; Wie, Jinhong; Hong, Chansik; Kim, Hyun Jin; Jeon, Ju-Hong; So, Insuk

2012-01-01

321

Capacitative calcium entry and TRPC channel proteins are expressed in rat distal pulmonary arterial smooth muscle.  

PubMed

Mammalian homologs of transient receptor potential (TRP) genes in Drosophila encode TRPC proteins, which make up cation channels that play several putative roles, including Ca2+ entry triggered by depletion of Ca2+ stores in endoplasmic reticulum (ER). This capacitative calcium entry (CCE) is thought to replenish Ca2+ stores and contribute to signaling in many tissues, including smooth muscle cells from main pulmonary artery (PASMCs); however, the roles of CCE and TRPC proteins in PASMCs from distal pulmonary arteries, which are thought to be the major site of pulmonary vasoreactivity, remain uncertain. As an initial test of the possibility that TRPC channels contribute to CCE and Ca2+ signaling in distal PASMCs, we measured [Ca2+]i by fura-2 fluorescence in primary cultures of myocytes isolated from rat intrapulmonary arteries (>4th generation). In cells perfused with Ca2+-free media containing cyclopiazonic acid (10 microM) and nifedipine (5 microM) to deplete ER Ca2+ stores and block voltage-dependent Ca2+ channels, restoration of extracellular Ca2+ (2.5 mM) caused marked increases in [Ca2+]i whereas MnCl2 (200 microM) quenched fura-2 fluorescence, indicating CCE. SKF-96365, LaCl3, and NiCl2, blocked CCE at concentrations that did not alter Ca2+ responses to 60 mM KCl (IC50 6.3, 40.4, and 191 microM, respectively). RT-PCR and Western blotting performed on RNA and protein isolated from distal intrapulmonary arteries and PASMCs revealed mRNA and protein expression for TRPC1, -4, and -6, but not TRPC2, -3, -5, or -7. Our results suggest that CCE through TRPC-encoded Ca2+ channels could contribute to Ca2+ signaling in myocytes from distal intrapulmonary arteries. PMID:14672922

Wang, Jian; Shimoda, L A; Sylvester, J T

2003-12-12

322

Cotranslational Partitioning of Nascent Prion Protein into Multiple Populations at the Translocation Channel  

Microsoft Academic Search

The decisive events that direct a single polypeptide such as the prion protein (PrP) to be synthesized at the endoplasmic reticulum in both fully translocated and transmembrane forms are poorly understood. In this study, we demonstrate that the topological heterogeneity of PrP is determined cotranslationally, while at the translocation channel. By evaluating sequential inter- mediates during PrP topogenesis, we find

Soo Jung Kim; Ramanujan S. Hegde

2002-01-01

323

Heart Rate Regulation by G Proteins Acting on the Cardiac Pacemaker Channel  

Microsoft Academic Search

Heart rate is determined by pacemaker currents, of which the most important is the hyperpolarization-activated current I_f. Heart rate and I_f are increased by beta-adrenergic agonists and decreased by muscarinic agonists released from cardiac sympathetic and vagal nerves, respectively. The hypothesis that the receptors for each agonist are directly coupled to I_f channels by G proteins was tested. Under substrate-free

A. Yatani; K. Okabe; J. Codina; L. Birnbaumer; A. M. Brown

1990-01-01

324

Prion channel proteins and their role in vacuolation and neurodegenerative diseases  

Microsoft Academic Search

The prion encephalopathies, which are characterized by neuropathological changes that include vacuolation, astrocytosis, the development of amyloid plaques and neuronal loss, are associated with the conversion of a normal cellular isoform of prion protein (PrPc) to an abnormal pathologic scrapie isoform (PrPSc). The use of PrP[106-126] and its isoforms in studies of channels in lipid bilayers has revealed that it

Joseph I. Kourie

2002-01-01

325

TMEM16A Protein: A New Identity for Ca2+-Dependent Cl? Channels  

NSDL National Science Digital Library

Ca+-dependent Cl? channels (CaCCs) play a variety of physiological roles in different organs and tissues, including transepithelial Cl? secretion, smooth muscle contraction, regulation of neuronal excitability, and transduction of sensory stimuli. The recent identification of TMEM16A protein as an important component of CaCCs should allow a better understanding of their physiological role, structure-function relationship, and regulatory mechanisms.

Loretta Ferrera (Istituto Giannina Gaslini); Antonella Caputo (Istituto Giannina Gaslini); Luis Galietta (Istituto Giannina Gaslini)

2010-12-01

326

The G protein-gated atrial K+ channel is stimulated by three distinct GIalpha-subunits  

Microsoft Academic Search

The gunanine nucleotide-binding protein, Gi, which inhibits adenylyl cyclase, has recently been shown to have three subtypes of the a-subunit, termed Gialpha-1, Gialpha-2 and Gialpha-3. They share 87-94% amino-acid sequence homology1-10 and so are difficult to separate from one another. Among other functions11,12-14, purified preparations activate K+ channels15-21 but there is confusion over which of the subtypes activates the muscarinic

Atsuko Yatani; Rafael Mattera; Juan Codina; Rolf Graf; Kouji Okabe; Elena Padrell; Ravi Iyengar; Arthur M. Brown; Lutz Birnbaumer

1988-01-01

327

Deuterium NMR of water in immobilized protein systems.  

PubMed Central

Deuterium NMR spectra are reported for lysozyme crystals, powders, and frozen solutions. At high water contents the spectrum is a superposition of a narrow central component and a quadrupole doublet. The quadrupole splitting and the relaxation rates of both components, monitored as a function of water content and temperature, are discussed in terms of models for the water-protein interaction. The anisotropy of the water molecule motion is clearly demonstrated by the deuterium quadrupole splitting observed in the protein single crystal, but such splittings were not found in protein powders and frozen protein solutions. We therefore suggest that the most useful view of such data is to consider the water-protein interactions at the surface to be mixed rapidly and that a distribution of interactions be invoked rather than an oversimplified view often taken of a two or n-site mixing where n is small.

Borah, B; Bryant, R G

1982-01-01

328

Strong Flows of Bottom Water in Abyssal Channels of the Atlantic  

NASA Astrophysics Data System (ADS)

Analysis of bottom water transport through the abyssal channels of the Atlantic Ocean is presented. The study is based on recent observations in the Russian expeditions and historical data. A strong flow of Antarctic Bottom Water from the Argentine Basin to the Brazil Basin through the Vema Channel is observed on the basis of lowered profilers and anchored buoys with current meters. The further flow of bottom water in the Brazil Basin splits in the northern part of the basin. Part of the bottom water flows to the East Atlantic through the Romanche and Chain fracture zones. The other part follows the bottom topography and flows to the northwester into the North American Basin. Part of the northwesterly flow propagates through the Vema Fracture Zone into the Northeastern Atlantic. This flow generally fills the bottom layer in the Northeastern Atlantic basins. The flows of bottom waters through the Romanche and Chain fracture zones do not spread to the Northeast Atlantic due to strong mixing in the equatorial zone and enhanced transformation of bottom water properties.

Morozov, E. G.

329

Manipulating L-type calcium channels in cardiomyocytes using split-intein protein transsplicing.  

PubMed

Manipulating expression of large genes (>6 kb) in adult cardiomyocytes is challenging because these cells are only efficiently transduced by viral vectors with a 4-7 kb packaging capacity. This limitation impedes understanding structure-function mechanisms of important proteins in heart. L-type calcium channels (LTCCs) regulate diverse facets of cardiac physiology including excitation-contraction coupling, excitability, and gene expression. Many important questions about how LTCCs mediate such multidimensional signaling are best resolved by manipulating expression of the 6.6 kb pore-forming ?1C-subunit in adult cardiomyocytes. Here, we use split-intein-mediated protein transsplicing to reconstitute LTCC ?1C-subunit from two distinct halves, overcoming the difficulty of expressing full-length ?1C in cardiomyocytes. Split-intein-tagged ?1C fragments encoding dihydropyridine-resistant channels were incorporated into adenovirus and reconstituted in cardiomyocytes. Similar to endogenous LTCCs, recombinant channels targeted to dyads, triggered Ca(2+) transients, associated with caveolin-3, and supported ?-adrenergic regulation of excitation-contraction coupling. This approach lowers a longstanding technical hurdle to manipulating large proteins in cardiomyocytes. PMID:24003157

Subramanyam, Prakash; Chang, Donald D; Fang, Kun; Xie, Wenjun; Marks, Andrew R; Colecraft, Henry M

2013-09-03

330

Large-scale fabrication of 4-nm-channel vertical protein-based ambipolar transistors.  

PubMed

We suggest a universal method for the mass production of nanometer-sized molecular transistors. This vertical-type device was fabricated using conventional photolithography and self-assembly methods and was processed in parallel fashion. We used this transistor to investigate the transport properties of a single layer of bovine serum albumin protein. This 4-nm-channel device exhibits low operating voltages, ambipolar behavior, and high gate sensitivity. The operation mechanism of this new device is suggested, and the charge transfer through the protein layer was explored. PMID:19265394

Mentovich, Elad D; Belgorodsky, Bogdan; Kalifa, Itsik; Cohen, Hagai; Richter, Shachar

2009-04-01

331

Highlights from recently determined structures of membrane proteins: a focus on channels and transporters  

PubMed Central

After decades of absent or lackluster growth, recent years have at long last witnessed an exponential growth in the number of novel membrane protein structures determined. Every single achievement has had a tremendous impact on the scientific community, typically providing an unprecedented wealth of information that only an atomic resolution structure can contribute to our molecular understanding of how a protein functions. Presented here is a review of some of the most exciting novel structures of channels and transporters determined by X-ray crystallography in the last two years, and a discussion of their analogies, differences and mechanistic implications.

Sciara, Giuliano; Mancia, Filippo

2012-01-01

332

Iterative Receiver in Time--Frequency Domain for Shallow Water Acoustic Channel  

NASA Astrophysics Data System (ADS)

Inter-symbol interference (ISI) caused by multi-path propagation, especially in shallow water channel, degrades the performance of underwater acoustic (UWA) communication systems. In this paper, we combine soft minimum mean squared error (MMSE) equalization and the serially concatenated trellis coded modulation (SCTCM) decoding to develop an iterative receiver in time--frequency domain (TFD) for underwater acoustic point to point communications. Based on sound speed profile (SSP) measured in the lake and finite-element ray (FER) tracing method (Bellhop), the shallow water channel is constructed to evaluate the performance of the proposed iterative receiver. The results suggest that the proposed iterative receiver can reduce the calculation complexity of the equalizer and obtain better performance using less receiving elements.

Zhao, Liang; Ge, Jianhua

2012-03-01

333

Water-soluble proteins of the human red cell membrane  

Microsoft Academic Search

Summary Procedures were developed for preparation of red cell membranes almost free of hemoglobin but with minimal loss of membrane proteins. Two water-soluble protein fractions are described, each constituting about 25% of the ghost protein. The first is ionically bonded and can be solubilized in water rapidly at pH 7.0 and more slowly at higher ionic strength solutions, with a

J. Th. Hoogeveen; R. Juliano; J. Coleman; A. Rothstein

1970-01-01

334

Lipid-Protein Interaction of the MscS Mechanosensitive Channel Examined by Scanning Mutagenesis  

PubMed Central

The mechanosensitive channel of small conductance (MscS) is a bacterial mechanosensitive channel that opens in response to rapid hypoosmotic stress. Since MscS can be opened solely by membrane stretch without help from any accessory protein, the lipid-protein interface must play a crucial role in sensing membrane tension. In this study, the hydrophobic residues in the lipid-protein interface were substituted one by one with a hydrophilic amino acid, asparagine, to modify the interaction between the protein and the lipid. Function of the mutant MscSs was examined by patch-clamp and hypoosmotic shock experiments. An increase in the gating threshold and a decrease in the viability on hypoosmotic shock were observed when the hydrophobic residues near either end of the first or the second transmembrane helix (TM1 or TM2) were replaced with asparagine. This observation indicates that the lipid-protein interaction at the ends of both helices (TM1 and TM2) is essential to MscS function.

Nomura, Takeshi; Sokabe, Masahiro; Yoshimura, Kenjiro

2006-01-01

335

Peptide and Protein Binding in the Axial Channel of Hsp104  

PubMed Central

The AAA+ molecular chaperone Hsp104 mediates the extraction of proteins from aggregates by unfolding and threading them through its axial channel in an ATP-driven process. An Hsp104-binding peptide selected from solid phase arrays enhanced the refolding of a firefly luciferase-peptide fusion protein. Analysis of peptide binding using tryptophan fluorescence revealed two distinct binding sites, one in each AAA+ module of Hsp104. As a further indication of the relevance of peptide binding to the Hsp104 mechanism, we found that it competes with the binding of a model unfolded protein, reduced carboxymethylated ?-lactalbumin. Inactivation of the pore loops in either AAA+ module prevented stable peptide and protein binding. However, when the loop in the first AAA+ was inactivated, stimulation of ATPase turnover in the second AAA+ module of this mutant was abolished. Drawing on these data, we propose a detailed mechanistic model of protein unfolding by Hsp104 in which an initial unstable interaction involving the loop in the first AAA+ module simultaneously promotes penetration of the substrate into the second axial channel binding site and activates ATP turnover in the second AAA+ module.

Lum, Ronnie; Niggemann, Monika; Glover, John R.

2008-01-01

336

Heat shock proteins and p53 play a critical role in K + channel-mediated tumor cell proliferation and apoptosis  

Microsoft Academic Search

Plasma membrane potassium (K+) channels are required for tumor cell proliferation and apoptosis. However, the signal transduction mechanisms underlying\\u000a K+ channel-dependent tumor cell proliferation or apoptosis remains elusive. Using HeLa and A2780 cells as study models, we tested\\u000a the hypothesis that apoptotic proteins are linked with K+ channel-dependent tumor cell cycle and apoptosis. The patch-clamping study using the whole-cell mode

Xiaobing Han; Fang Wang; Weixing Yao; Hui Xing; Danhui Weng; Xiaohong Song; Gang Chen; Ling Xi; Tao Zhu; Jianfeng Zhou; Gang Xu; Shixuan Wang; Li Meng; Costantino Iadecola; Gang Wang; Ding Ma

2007-01-01

337

Lattice Boltzmann model for shallow water flows in curved and meandering channels  

Microsoft Academic Search

Meandering channel flows are simulated using two-dimensional lattice Boltzmann models (LBM) for the shallow water equations. A boundary approach is designed for curved boundary treatment, which is applicable to no-slip, semi-slip and slip boundaries at a second-order accuracy. The large eddy simulation model is added in the lattice Boltzmann model, so that the turbulence can be taken into account and

Haifei Liu; Guo Jian Zhou; Richard Burrows

2009-01-01

338

Simultaneous Iterative Water-Filling for Gaussian Frequency-Selective Interference Channels  

Microsoft Academic Search

The sequential iterative water-filling algorithm (IWFA) proposed by Yu et al. is by now a popular low-complexity algorithm to compute the Nash equilibrium point of the power allocation game in a Gaussian frequency-selective multiuser interference channel. The algorithm is based on a distributed sequential updating where, at each iteration, the users choose their power allocation, one after the other. However,

Gesualdo Scutari; Daniel P. Palomar; Sergio Barbarossa

2006-01-01

339

Gas-discharge probe microscopy of water-carrying channels in wood  

NASA Astrophysics Data System (ADS)

We have used a gas-discharge imaging technique to study the water transport channels (tracheids) in wood samples. Results obtained for the samples of bitch and aspen show features of this variant of the probe microscopy and show its additional possibilities as compared to optical microscopy. It is concluded that gas-discharge probe microscopy can be used for additional diagnostics of the structure of plant and animal tissues.

Ivanov-Omskii, V. I.; Ivanova, E. I.

2012-04-01

340

Increased migration and metastatic potential of tumor cells expressing aquaporin water channels  

Microsoft Academic Search

Aquaporin (AQP) water channels are expressed in high-grade tumor cells of different tissue origins. Based on the involvement of AQPs in angio- genesis and cell migration, we tested whether AQP expression in tumor cells might enhance their migra- tion and metastatic potential. Transfection of B16F10 and 4T1 tumor cells with AQP1 did not affect their appearance, size, growth, or substrate

Jie Hu; A. S. Verkman

2006-01-01

341

Impact of Salt and Water on Protein Structural Dynamics  

NASA Astrophysics Data System (ADS)

Water is known as the lubricant of life. Without water, most proteins would lose their biological functions. Extensive studies have been carried out on how high concentration salts (dissolved in water) alter the stability and solubility of proteins. Such effects are thought to be mediated via salt-water interactions and water-protein interactions. This classic research field is known as the Hofmeister Series. We report the effects of Hofmeister Salts on the structural dynamics of proteins. Photoactive yellow protein (PYP), a bacterial blue light photoreceptor protein, is employed as a model system in this study. Time-resolved FTIR spectroscopic techniques allow us to probe the structural changes in proteins. Our data reveal that high concentration salt solutions alter the proton transfer pathway and suppress conformational changes in PYP upon photo-excitation. This study opens up a new dimension in the field of Hofmeister series. Further theoretical and experimental studies are needed in order to understand the dynamic properties of salt-water interactions and water-protein interactions.

Thubagere, Anu; Kelemen, Lorand; Nie, Beining; Kaledhonkar, Sandip; Xie, Aihua

2008-03-01

342

Cloning and characterization of a zebrafish homologue of human AQP1: a bifunctional water and gas channel  

PubMed Central

The mammalian aquaporins AQP1, AQP4, and AQP5 have been shown to function not only as water channels but also as gas channels. Zebrafish have two genes encoding an AQP1 homologue, aqp1a and aqp1b. In the present study, we cloned the cDNA that encodes the zebrafish protein Aqp1a from the 72-h postfertilization (hpf) embryo of Danio rerio, as well as from the swim bladder of the adult. The deduced amino-acid sequence of aqp1a consists of 260 amino acids and is 59% identical to human AQP1. By analyzing the genomic DNA sequence, we identified four exons in the aqp1a gene. By in situ hybridization, aqp1a is expressed transiently in the developing vasculature and in erythrocytes from 16 to 48 h of development. Later, at 72 hpf, aqp1a is expressed in dermal ionocytes and in the swim bladder. Western blot analysis of adult tissues reveals that Aqp1a is most highly expressed in the eye and swim bladder. Xenopus oocytes expressing aqp1a have a channel-dependent (*) osmotic water permeability (Pf*) that is indistinguishable from that of human AQP1. On the basis of the magnitude of the transient change in surface pH (?pHS) that were recorded as the oocytes were exposed to either CO2 or NH3, we conclude that zebrafish Aqp1a is permeable to both CO2 and NH3. The ratio (?pHS*)CO2/Pf* is about half that of human AQP1, and the ratio (?pHS*)NH3/Pf* is about one-quarter that of human AQP1. Thus, compared with human AQP1, zebrafish Aqp1a has about twice the selectivity for CO2 over NH3.

Chen, Li-Ming; Zhao, Jinhua; Musa-Aziz, Raif; Pelletier, Marc F.; Drummond, Iain A.

2010-01-01

343

Unstructured to structured transition of an intrinsically disordered protein peptide in coupling Ca2+-sensing and SK channel activation  

PubMed Central

Most proteins, such as ion channels, form well-organized 3D structures to carry out their specific functions. A typical voltage-gated potassium channel subunit has six transmembrane segments (S1–S6) to form the voltage-sensing domain and the pore domain. Conformational changes of these domains result in opening of the channel pore. Intrinsically disordered (ID) proteins/peptides are considered equally important for the protein functions. However, it is difficult to explore the structural features underlying the functions of ID proteins/peptides by conventional methods, such as X-ray crystallography, because of the flexibility of their secondary structures. Unlike voltage-gated potassium channels, families of small- and intermediate-conductance Ca2+-activated potassium (SK/IK) channels with important roles in regulating membrane excitability are activated exclusively by Ca2+-bound calmodulin (CaM). Upon binding of Ca2+ to CaM, a 2 × 2 structure forms between CaM and the CaM-binding domain. A channel fragment that connects S6 and the CaM-binding domain is not visible in the protein crystal structure, suggesting that this fragment is an ID fragment. Here we show that the conformation of the ID fragment in SK channels becomes readily identifiable in the presence of NS309, the most potent compound that potentiates the channel activities. This well-defined conformation of the ID fragment, stabilized by NS309, increases the channel open probability at a given Ca2+ concentration. Our results demonstrate that the ID fragment, itself a target for drugs modulating SK channel activities, plays a unique role in coupling Ca2+ sensing by CaM and mechanical opening of SK channels.

Zhang, Miao; Pascal, John M.; Zhang, Ji-Fang

2013-01-01

344

AMP-activated protein kinase in BK-channel regulation and protection against hearing loss following acoustic overstimulation.  

PubMed

The energy-sensing AMP-activated serine/threonine protein kinase (AMPK) confers cell survival in part by stimulation of cellular energy production and limitation of cellular energy utilization. AMPK-sensitive functions further include activities of epithelial Na+ channel ENaC and voltage-gated K+ channel KCNE1/KCNQ1. AMPK is activated by an increased cytosolic Ca2+ concentration. The present study explored whether AMPK regulates the Ca2+-sensitive large conductance and voltage-gated potassium (BK) channel. cRNA encoding BK channel was injected into Xenopus oocytes with and without additional injection of wild-type AMPK (AMPK?1+AMPK?1+AMPK?1), constitutively active AMPK?R70Q, or inactive AMPK?K45R. BK-channel activity was determined utilizing the 2-electrode voltage-clamp. Moreover, BK-channel protein abundance in the cell membrane was determined by confocal immunomicroscopy. As BK channels are expressed in outer hair cells (OHC) of the inner ear and lack of BK channels increases noise vulnerability, OHC BK-channel expression was examined by immunohistochemistry and hearing function analyzed by auditory brain stem response measurements in AMPK?1-deficient mice (ampk-/-) and in wild-type mice (ampk+/+). As a result, coexpression of AMPK or AMPK?R70Q but not of AMPK?K45R significantly enhanced BK-channel-mediated currents and BK-channel protein abundance in the oocyte cell membrane. BK-channel expression in the inner ear was lower in ampk-/- mice than in ampk+/+ mice. The hearing thresholds prior to and immediately after an acoustic overexposure were similar in ampk-/- and ampk+/+ mice. However, the recovery from the acoustic trauma was significantly impaired in ampk-/- mice compared to ampk+/+ mice. In summary, AMPK is a potent regulator of BK channels. It may thus participate in the signaling cascades that protect the inner ear from damage following acoustic overstimulation. PMID:22767231

Föller, Michael; Jaumann, Mirko; Dettling, Juliane; Saxena, Ambrish; Pakladok, Tatsiana; Munoz, Carlos; Ruth, Peter; Sopjani, Mentor; Seebohm, Guiscard; Rüttiger, Lukas; Knipper, Marlies; Lang, Florian

2012-07-05

345

Modulation of proton transfer in the water wire of dioxolane-linked gramicidin channels by lipid membranes.  

PubMed Central

Proton conductance (g(H)) in single SS stereoisomers of dioxolane-linked gramicidin A (gA) channels were measured in different phospholipid bilayers at different HCl concentrations. In particular, measurements were obtained in bilayers made of 1,2-diphytanoyl 3-phosphocholine (DiPhPC) or its ethylated derivative 1,2-diphytanoyl 3-ethyl-phosphocholine (et-DiPhPC,). The difference between these phospholipids is that in et-DiPhPC one of the phosphate oxygens is covalently linked to an ethyl group and cannot be protonated. In relatively dilute acid solutions, g(H) in DiPhPC is significantly higher than in et-DiPhPC. At high acid concentrations, g(H) is the same in both diphytanoyl bilayers. Such differences in g(H) can be accounted for by surface charge effects at the membrane/solution interfaces. In the linear portion of the log g(H)-log [H] relationship, g(H) values in diphytanoyl bilayers were significantly larger (approximately 10-fold) than in neutral glyceryl monooleate (GMO) membranes. The slopes of the linear log-log relationships between g(H) and [H] in diphytanoyl and GMO bilayers are essentially the same (approximately 0.76). This slope is significantly lower than the slope of the log-log plot of proton conductivity versus proton concentration in aqueous solutions (approximately 1.00). Because the chemical composition of the membrane-channel/solution interface is strikingly different in GMO and diphytanoyl bilayers, the reduced slope in g(H)-[HCl] relationships may be a characteristic of proton transfer in the water wire inside the SS channel. Values of g(H) in diphytanoyl bilayers were also significantly larger than in membranes made of the more common biological phospholipids 1-palmitoyl 2-oleoyl phosphocholine (POPC) or 1-palmitoyl 2-oleoyl phosphoethanolamine (POPE). These differences, however, cannot be accounted for by different surface charge effects or by different internal dipole potentials. On the other hand, maximum g(H) measured in the SS channel does not depend on the composition of the bilayer and is determined essentially by the reduced mobility of protons in concentrated acid solutions. Finally, no experimental evidence was found in support of a lateral proton movement at the phospholipid/solution interface contributing to g(H) in single SS channels. Protein-lipid interactions are likely to modulate g(H) in the SS channel.

de Godoy, C M; Cukierman, S

2001-01-01

346

Water dynamics at protein interfaces: ultrafast optical Kerr effect study.  

PubMed

The behavior of water molecules surrounding a protein can have an important bearing on its structure and function. Consequently, a great deal of attention has been focused on changes in the relaxation dynamics of water when it is located at the protein surface. Here we use the ultrafast optical Kerr effect to study the H-bond structure and dynamics of aqueous solutions of proteins. Measurements are made for three proteins as a function of concentration. We find that the water dynamics in the first solvation layer of the proteins are slowed by up to a factor of 8 in comparison to those in bulk water. The most marked slowdown was observed for the most hydrophilic protein studied, bovine serum albumin, whereas the most hydrophobic protein, trypsin, had a slightly smaller effect. The terahertz Raman spectra of these protein solutions resemble those of pure water up to 5 wt % of protein, above which a new feature appears at ~80 cm(-1), which is assigned to a bending of the protein amide chain. PMID:21988177

Mazur, Kamila; Heisler, Ismael A; Meech, Stephen R

2011-10-11

347

A caveolin-binding domain in the HCN4 channels mediates functional interaction with caveolin proteins.  

PubMed

Pacemaker (HCN) channels have a key role in the generation and modulation of spontaneous activity of sinoatrial node myocytes. Previous work has shown that compartmentation of HCN4 pacemaker channels within caveolae regulates important functions, but the molecular mechanism responsible is still unknown. HCN channels have a conserved caveolin-binding domain (CBD) composed of three aromatic amino acids at the N-terminus; we sought to evaluate the role of this CBD in channel-protein interaction by mutational analysis. We generated two HCN4 mutants with a disrupted CBD (Y259S, F262V) and two with conservative mutations (Y259F, F262Y). In CHO cells expressing endogenous caveolin-1 (cav-1), alteration of the CBD shifted channels activation to more positive potentials, slowed deactivation and made Y259S and F262V mutants insensitive to cholesterol depletion-induced caveolar disorganization. CBD alteration also caused a significant decrease of current density, due to a weaker HCN4-cav-1 interaction and accumulation of cytoplasmic channels. These effects were absent in mutants with a preserved CBD. In caveolin-1-free fibroblasts, HCN4 trafficking was impaired and current density reduced with all constructs; the activation curve of F262V was not altered relative to wt, and that of Y259S displayed only half the shift than in CHO cells. The conserved CBD present in all HCN isoforms mediates their functional interaction with caveolins. The elucidation of the molecular details of HCN4-cav-1 interaction can provide novel information to understand the basis of cardiac phenotypes associated with some forms of caveolinopathies. PMID:22659290

Barbuti, Andrea; Scavone, Angela; Mazzocchi, Nausicaa; Terragni, Benedetta; Baruscotti, Mirko; Difrancesco, Dario

2012-05-31

348

Inhibition of G protein-activated inwardly rectifying K+ channels by different classes of antidepressants.  

PubMed

Various antidepressants are commonly used for the treatment of depression and several other neuropsychiatric disorders. In addition to their primary effects on serotonergic or noradrenergic neurotransmitter systems, antidepressants have been shown to interact with several receptors and ion channels. However, the molecular mechanisms that underlie the effects of antidepressants have not yet been sufficiently clarified. G protein-activated inwardly rectifying K(+) (GIRK, Kir3) channels play an important role in regulating neuronal excitability and heart rate, and GIRK channel modulation has been suggested to have therapeutic potential for several neuropsychiatric disorders and cardiac arrhythmias. In the present study, we investigated the effects of various classes of antidepressants on GIRK channels using the Xenopus oocyte expression assay. In oocytes injected with mRNA for GIRK1/GIRK2 or GIRK1/GIRK4 subunits, extracellular application of sertraline, duloxetine, and amoxapine effectively reduced GIRK currents, whereas nefazodone, venlafaxine, mianserin, and mirtazapine weakly inhibited GIRK currents even at toxic levels. The inhibitory effects were concentration-dependent, with various degrees of potency and effectiveness. Furthermore, the effects of sertraline were voltage-independent and time-independent during each voltage pulse, whereas the effects of duloxetine were voltage-dependent with weaker inhibition with negative membrane potentials and time-dependent with a gradual decrease in each voltage pulse. However, Kir2.1 channels were insensitive to all of the drugs. Moreover, the GIRK currents induced by ethanol were inhibited by sertraline but not by intracellularly applied sertraline. The present results suggest that GIRK channel inhibition may reveal a novel characteristic of the commonly used antidepressants, particularly sertraline, and contributes to some of the therapeutic effects and adverse effects. PMID:22164246

Kobayashi, Toru; Washiyama, Kazuo; Ikeda, Kazutaka

2011-12-02

349

Inhibition of G Protein-Activated Inwardly Rectifying K+ Channels by Different Classes of Antidepressants  

PubMed Central

Various antidepressants are commonly used for the treatment of depression and several other neuropsychiatric disorders. In addition to their primary effects on serotonergic or noradrenergic neurotransmitter systems, antidepressants have been shown to interact with several receptors and ion channels. However, the molecular mechanisms that underlie the effects of antidepressants have not yet been sufficiently clarified. G protein-activated inwardly rectifying K+ (GIRK, Kir3) channels play an important role in regulating neuronal excitability and heart rate, and GIRK channel modulation has been suggested to have therapeutic potential for several neuropsychiatric disorders and cardiac arrhythmias. In the present study, we investigated the effects of various classes of antidepressants on GIRK channels using the Xenopus oocyte expression assay. In oocytes injected with mRNA for GIRK1/GIRK2 or GIRK1/GIRK4 subunits, extracellular application of sertraline, duloxetine, and amoxapine effectively reduced GIRK currents, whereas nefazodone, venlafaxine, mianserin, and mirtazapine weakly inhibited GIRK currents even at toxic levels. The inhibitory effects were concentration-dependent, with various degrees of potency and effectiveness. Furthermore, the effects of sertraline were voltage-independent and time-independent during each voltage pulse, whereas the effects of duloxetine were voltage-dependent with weaker inhibition with negative membrane potentials and time-dependent with a gradual decrease in each voltage pulse. However, Kir2.1 channels were insensitive to all of the drugs. Moreover, the GIRK currents induced by ethanol were inhibited by sertraline but not by intracellularly applied sertraline. The present results suggest that GIRK channel inhibition may reveal a novel characteristic of the commonly used antidepressants, particularly sertraline, and contributes to some of the therapeutic effects and adverse effects.

Kobayashi, Toru; Washiyama, Kazuo; Ikeda, Kazutaka

2011-01-01

350

Laser-induced acoustic wave generation\\/propagation\\/interaction in water in various internal channels  

Microsoft Academic Search

Short pulsed laser-induced single acoustic wave generation, propagation, interaction within a water-filled internal channel\\u000a are experimentally and numerically studied. A large-area, short-duration, single-plane acoustic wave was generated by the\\u000a thermoelastic interaction of a homogenized nanosecond pulsed laser beam with a liquid–solid interface and propagated at the\\u000a speed of sound in water. Laser flash Schlieren photography was used to visualize the

Seung Hwan Ko; Daeho Lee; Heng Pan; Sang-Gil Ryu; Costas P. Grigoropoulos; Nick Kladias; Elias Panides; Gerald A. Domoto

2010-01-01

351

Channeling of aminoacyl-tRNA for protein synthesis in vivo  

SciTech Connect

Channeling, the direct transfer of metabolic intermediates from one enzyme to another in a pathway, has received increased attention as an explanation for the high efficiency of cellular processes. The known structural organization of the protein biosynthetic machinery, and a recent suggestion that aminoacyl-tRNAs may be channeled, has led us to devise a direct test of this possibility. By employing the technique of electroporation, conditions were established for the introduction of aminoacyl-tRNAs into Chinese hamster ovary (CHO) cells. We show, by coelectroporation of various combinations of free {sup 14}C amino acids and {sup 3}H aminoacyl-tRNAs, that whereas the free amino acids serve as effective precursors for protein synthesis, the exogenous aminoacyl-tRNAs are utilized poorly, if at all. The lack of incorporation into protein from added aminoacyl-tRNAs is not due to their leakage from the cell, to their instability, or to their damage during electroporation. Furthermore, in contrast to the findings with intact cells, extracts of CHO cells incorporate both free amino acids and aminoacyl-tRNAs into protein with similar efficiencies. Based on these observations, the authors conclude that the inability of exogenous aminoacyl-tRNAs to serve as precursors for protein synthesis is due to the structural organization of intact cells that leads to channeling of this substrate in vivo. Thus, they propose that endogenously synthesized aminoacyl-tRNA is directly transferred from aminoacyl-tRNA synthetase to elongation factor to ribosome without dissociation into the cell fluid, and as a consequence, usage of exogenously introduced molecules is precluded.

Negrutskii, B.S.; Deutscher, M.P. (Department of Biochemistry, University of Connecticut Health Center, Farmington (USA))

1991-06-01

352

Cytoplasmic Unsaturated Free Fatty Acids Inhibit ATP-dependent Gating of the G Protein-gated K+ Channel  

Microsoft Academic Search

This study reports the identification of an endogenous inhibitor of the G protein-gated (K ACh ) chan- nel and its effect on the K ACh channel kinetics. In the presence of acetylcholine in the pipette, K ACh channels in in- side-out atrial patches were activated by applying GTP to the cytoplasmic side of the membrane. In these patches, addition of

Donghee Kim; Apisate Pleumsamran

2000-01-01

353

Patients with autosomal nephrogenic diabetes insipidus homozygous for mutations in the aquaporin 2 water-channel gene  

SciTech Connect

Mutations in the X-chromosomal V2 receptor gene are known to cause nephrogenic diabetes insipidus (NDI). Besides the X-linked form, an autosomal mode of inheritance has been described. Recently, mutations in the autosomal gene coding for water-channel aquaporin 2 (AQP2) of the renal collecting duct were reported in an NDI patient. In the present study, missense mutations and a single nucleotide deletion in the aquaporin 2 gene of three NDI patients from consanquineous matings are described. Expression studies in Xenopus oocytes showed that the missense AQP2 proteins are nonfunctional. These results prove that mutations in the AQP2 gene cause autosomal recessive NDI. 32 refs., 4 figs.

Lieburg, A.F. van; Verdijk, M.A.J.; Knoers, V.V.A.M.; Monnens, L.A.H.; Oost, B.A. van; Os, C.H. van; Deen, P.M.T. [Univ. of Nijmegen (Netherlands); Essen, A.J. van [Univ. of Groningen (Netherlands); Proesmans, W. [Univ. of Leuven (Belgium); Mallmann, R. [Univ. of Bonn (Germany)

1994-10-01

354

Inhibition of synaptic transmission and G protein modulation by synthetic CaV2.2 Ca2+ channel peptides  

PubMed Central

Abstract Modulation of presynaptic voltage-dependent Ca2+ channels is a major means of controlling neurotransmitter release. The CaV2.2 Ca2+ channel subunit contains several inhibitory interaction sites for G?? subunits, including the amino terminal (NT) and I–II loop. The NT and I–II loop have also been proposed to undergo a G protein-gated inhibitory interaction, whilst the NT itself has also been proposed to suppress CaV2 channel activity. Here, we investigate the effects of an amino terminal (CaV2.2[45–55]) ‘NT peptide’ and a I–II loop alpha interaction domain (CaV2.2[377–393]) ‘AID peptide’ on synaptic transmission, Ca2+ channel activity and G protein modulation in superior cervical ganglion neurones (SCGNs). Presynaptic injection of NT or AID peptide into SCGN synapses inhibited synaptic transmission and also attenuated noradrenaline-induced G protein modulation. In isolated SCGNs, NT and AID peptides reduced whole-cell Ca2+ current amplitude, modified voltage dependence of Ca2+ channel activation and attenuated noradrenaline-induced G protein modulation. Co-application of NT and AID peptide negated inhibitory actions. Together, these data favour direct peptide interaction with presynaptic Ca2+ channels, with effects on current amplitude and gating representing likely mechanisms responsible for inhibition of synaptic transmission. Mutations to residues reported as determinants of Ca2+ channel function within the NT peptide negated inhibitory effects on synaptic transmission, Ca2+ current amplitude and gating and G protein modulation. A mutation within the proposed QXXER motif for G protein modulation did not abolish inhibitory effects of the AID peptide. This study suggests that the CaV2.2 amino terminal and I–II loop contribute molecular determinants for Ca2+ channel function; the data favour a direct interaction of peptides with Ca2+ channels to inhibit synaptic transmission and attenuate G protein modulation.

Bucci, Giovanna; Mochida, Sumiko; Stephens, Gary J

2011-01-01

355

Controls on the Basal Water Pressure in Subglacial Channels Near the Margin of the Greenland Ice Sheet  

Microsoft Academic Search

Assuming a channelized drainage system in steady state, we investigate the influence of enhanced surface melting on the water pressure in subglacial channels, compared to that of changes in conduit geometry, ice rheology and catchment variations. The analysis is carried out for a specific part of the western Greenland ice-sheet margin between 66 degrees N and 66 degrees 30' N

Andreas P. Ahlstrøm; Johan J. Mohr; Niels Reeh; Erik Lintz Christensen; Roger Le B. Hooke

2005-01-01

356

Modulation of glycine-activated ion channel function by G-protein betagamma subunits.  

PubMed

Glycine receptors (GlyRs), together with GABA(A) and nicotinic acetylcholine (ACh) receptors, form part of the ligand-activated ion channel superfamily and regulate the excitability of the mammalian brain stem and spinal cord. Here we report that the ability of the neurotransmitter glycine to gate recombinant and native ionotropic GlyRs is modulated by the G protein betagamma dimer (Gbetagamma). We found that the amplitude of the glycine-activated Cl- current was enhanced after application of purified Gbetagamma or after activation of a G protein-coupled receptor. Overexpression of three distinct G protein alpha subunits (Galpha), as well as the Gbetagamma scavenger peptide ct-GRK2, significantly blunted the effect of G protein activation. Single-channel recordings from isolated membrane patches showed that Gbetagamma increased the GlyR open probability (nP(o)). Our results indicate that this interaction of Gbetagamma with GlyRs regulates both motor and sensory functions in the central nervous system. PMID:12858180

Yevenes, Gonzalo E; Peoples, Robert W; Tapia, Juan C; Parodi, Jorge; Soto, Ximena; Olate, Juan; Aguayo, Luis G

2003-08-01

357

Crystal Structure of the Mammalian GIRK2 K + Channel and Gating Regulation by G Proteins, PIP 2, and Sodium  

Microsoft Academic Search

G protein-gated K{sup +} channels (Kir3.1--Kir3.4) control electrical excitability in many different cells. Among their functions relevant to human physiology and disease, they regulate the heart rate and govern a wide range of neuronal activities. Here, we present the first crystal structures of a G protein-gated K{sup +} channel. By comparing the wild-type structure to that of a constitutively active

Roderick MacKinnon

2011-01-01

358

Physiological Roles and Diseases of Tmem16 / Anoctamin Proteins: Are They All Chloride Channels?  

PubMed Central

The Tmem16 gene family was first identified by bioinformatic analysis in 2004. In 2008, it was shown independently by 3 laboratories that the first two members (Tmem16A and Tmem16B) of this 10-gene family are Ca2+-activated Cl- channels. Because these proteins are thought to have 8 transmembrane domains and be anion-selective channels, the alternative name, Anoctamin (anion and octa=8), has been proposed. However, it remains unclear whether all members of this family are, in fact, anion channels or have the same 8-transmembrane domain topology. Since 2008, there have been nearly 100 papers published on this family. The excitement about Tmem16 proteins has been enhanced by the finding that Ano1 has been linked to cancer, mutations in Ano5 are linked to several forms of muscular dystrophy (LGMDL2 and MMD-3), mutations in Ano10 are linked to autosomal recessive spinocerebellar ataxia, and mutations in Ano6 are linked to Scott Syndrome, a rare bleeding disorder. Here we review some of the recent developments in understanding the physiology and structure-function of the Tmem16 family.

Duran, Charity; Hartzell, H. Criss

2013-01-01

359

Pentameric Assembly of Potassium Channel Tetramerization Domain-Containing Protein 5 (KCTD5)  

PubMed Central

We report the X-ray crystal structure of human potassium channel tetramerization domain-containing protein 5 (KCTD5), the first member of the family to be so characterized. Four findings were unexpected. First, the structure reveals assemblies of five subunits while tetramers were anticipated; pentameric stoichiometry is observed also in solution by scanning transmission electron microscopy mass analysis and analytical ultracentrifugation. Second, the same Bric-a-brac, Tramtrack, Broad Complex (BTB) domain surface mediates assembly of five KCTD5 and four voltage-gated potassium (Kv) channel subunits; four amino acid differences appear crucial. Third, KCTD5 complexes have well-defined N- and C-terminal modules separated by a flexible linker that swivels ~30°; the C-module shows a new fold and is required to bind Golgi re-assembling stacking protein 55 with ~1 ?M affinity as judged by surface plasmon resonance and ultracentrifugation. Fourth, despite the homology reflected in its name, KCTD5 does not impact operation of Kv4.2, Kv3.4, Kv2.1 or Kv1.2 channels.

Dementieva, Irina S.; Tereshko, Valentina; McCrossan, Zoe A.; Solomaha, Elena; Araki, Daniel; Xu, Chen; Grigorieff, Nikolaus; Goldstein, Steve A. N.

2009-01-01

360

Constructed molecular sensor to enhance metal detection by bacterial ribosomal switch-ion channel protein interaction.  

PubMed

Molecular biosensors are useful tools that detect metal ions or other potentially toxic chemicals. However, the efficiency of conventional sensors is limited in mixed metals substrates, which is the common way they are found in nature. The use of biosensors constructed from genetically modified living microbial systems has the potential of providing sensitive detection systems for specific toxic targets. Consequently, our investigation was aimed at assembling different genetic building blocks to produce a focused microbial biosensor with the ability to detect specific metals. This objective was achieved by using a synthetic biology approach. Our genetic building blocks, including a synchronized ribosomal switch-iron ion channel, along with sequences of promoters, metal-binding proteins (Fe, Pb), ribosomal binding sites, yellow fluorescence reporter protein (YFRP), and terminators, were constructed within the same biobrick in Escherichia coli. We used an rpoS ribosomal switch containing an aptamer, which responds to the specific metal ligands, in synchronization with an iron ion channel, TonB. This switch significantly stimulates translation, as expressed by higher fluorescence, number of colonies, and concentration of RNA in E. coli. The positive results show the effectiveness of using genetically tailored synchronized ribosomal switch-ion channels to construct microbial biosensors to detect specific metals, as tested in iron solutions. PMID:22300511

Cuero, Raul; Lilly, J; McKay, David S

2012-01-24

361

Pentameric assembly of potassium channel tetramerization domain-containing protein 5.  

PubMed

We report the X-ray crystal structure of human potassium channel tetramerization domain-containing protein 5 (KCTD5), the first member of the family to be so characterized. Four findings were unexpected. First, the structure reveals assemblies of five subunits while tetramers were anticipated; pentameric stoichiometry is observed also in solution by scanning transmission electron microscopy mass analysis and analytical ultracentrifugation. Second, the same BTB (bric-a-brac, tramtrack, broad complex) domain surface mediates the assembly of five KCTD5 and four voltage-gated K(+) (Kv) channel subunits; four amino acid differences appear crucial. Third, KCTD5 complexes have well-defined N- and C-terminal modules separated by a flexible linker that swivels by approximately 30 degrees; the C-module shows a new fold and is required to bind Golgi reassembly stacking protein 55 with approximately 1 microM affinity, as judged by surface plasmon resonance and ultracentrifugation. Fourth, despite the homology reflected in its name, KCTD5 does not impact the operation of Kv4.2, Kv3.4, Kv2.1, or Kv1.2 channels. PMID:19361449

Dementieva, Irina S; Tereshko, Valentina; McCrossan, Zoe A; Solomaha, Elena; Araki, Daniel; Xu, Chen; Grigorieff, Nikolaus; Goldstein, Steve A N

2009-01-23

362

Channel water balance and exchange with subsurface flow along a mountain headwater stream in Montana, United States  

Microsoft Academic Search

Channel water balances of contiguous reaches along streams represent a poorly understood scale of stream-subsurface interaction. We measured reach water balances along a headwater stream in Montana, United States, during summer base flow recessions. Reach water balances were estimated from series of tracer tests in 13 consecutive reaches delineated evenly along a 2.6 km valley segment. For each reach, we

R. A. Payn; M. N. Gooseff; B. L. McGlynn; K. E. Bencala; S. M. Wondzell

2009-01-01

363

Expression of G-protein inwardly rectifying potassium channels (GIRKs) in lung cancer cell lines  

PubMed Central

Background Previous data from our laboratory has indicated that there is a functional link between the ?-adrenergic receptor signaling pathway and the G-protein inwardly rectifying potassium channel (GIRK1) in human breast cancer cell lines. We wanted to determine if GIRK channels were expressed in lung cancers and if a similar link exists in lung cancer. Methods GIRK1-4 expression and levels were determined by reverse transcription polymerase chain reaction (RT-PCR) and real-time PCR. GIRK protein levels were determined by western blots and cell proliferation was determined by a 5-bromo-2'-deoxyuridine (BrdU) assay. Results GIRK1 mRNA was expressed in three of six small cell lung cancer (SCLC) cell lines, and either GIRK2, 3 or 4 mRNA expression was detected in all six SCLC cell lines. Treatment of NCI-H69 with ?2-adrenergic antagonist ICI 118,551 (100 ?M) daily for seven days led to slight decreases of GIRK1 mRNA expression levels. Treatment of NCI-H69 with the ?-adrenergic agonist isoproterenol (10 ?M) decreased growth rates in these cells. The GIRK inhibitor U50488H (2 ?M) also inhibited proliferation, and this decrease was potentiated by isoproterenol. In the SCLC cell lines that demonstrated GIRK1 mRNA expression, we also saw GIRK1 protein expression. We feel these may be important regulatory pathways since no expression of mRNA of the GIRK channels (1 & 2) was found in hamster pulmonary neuroendocrine cells, a suggested cell of origin for SCLC, nor was GIRK1 or 2 expression found in human small airway epithelial cells. GIRK (1,2,3,4) mRNA expression was also seen in A549 adenocarcinoma and NCI-H727 carcinoid cell lines. GIRK1 mRNA expression was not found in tissue samples from adenocarcinoma or squamous cancer patients, nor was it found in NCI-H322 or NCI-H441 adenocarcinoma cell lines. GIRK (1,3,4) mRNA expression was seen in three squamous cell lines, GIRK2 was only expressed in one squamous cell line. However, GIRK1 protein expression was not seen in any non-SCLC cells. Conclusion We feel that this data may indicate that stimulation of GIRK1 or GIRK2 channels may be important in lung cancer. Stimulation of GIRK channels and ?-adrenergic signaling may activate similar signaling pathways in both SCLC and breast cancer, but lead to different results.

Plummer, Howard K; Dhar, Madhu S; Cekanova, Maria; Schuller, Hildegard M

2005-01-01

364

Channels Formed by Botulinum, Tetanus, and Diphtheria Toxins in Planar Lipid Bilayers: Relevance to Translocation of Proteins across Membranes  

NASA Astrophysics Data System (ADS)

The heavy chains of both botulinum neurotoxin type B and tetanus toxin form channels in planar bilayer membranes. These channels have pH-dependent and voltage-dependent properties that are remarkably similar to those previously described for diphtheria toxin. Selectivity experiments with anions and cations show that the channels formed by the heavy chains of all three toxins are large; thus, these channels could serve as ``tunnel proteins'' for translocation of active peptide fragments. These findings support the hypothesis that the active fragments of botulinum neurotoxin and tetanus toxin, like that of diphtheria toxin, are translocated across the membranes of acidic vesicles.

Hoch, David H.; Romero-Mira, Miryam; Ehrlich, Barbara E.; Finkelstein, Alan; Dasgupta, Bibhuti R.; Simpson, Lance L.

1985-03-01

365

The effect of hydrophobic and hydrophilic channel walls on the structure and diffusion of water and ions  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations are carried out to determine the effects of channel wall structure on water and ion properties. We compare hydrophobic (Lennard-Jones 5-3 and atomic) and molecular-hydrophilic cylindrical pores of 2-6 Å in effective radius, relevant to the study of most significant biological ion channels including gramicidin A, ACh, and potassium channels, and to the study of many microporous materials. Large variations in levels of self-diffusion and rotational correlation within hydrophobic channels are explained in terms of water geometry, hydrogen bonding, and dipole correlation. The differing levels of water structure and self-diffusion in hydrophobic and hydrophilic pores arise because of marked differences in the preferred orientation of water dipole moments, and due to hydrogen bonding with molecules on the pore lining. Axial sodium ion diffusion does not experience large variations with pore size, despite anomalous stability in moderate-sized hydrophobic pores. We attribute this to the ability of ions to diffuse along troughs of water density. Ion diffusion along the pore axis exhibits a general increase with channel radius in hydrophobic channels but remains fairly low in hydrophilic channels.

Allen, T. W.; Kuyucak, S.; Chung, S.-H.

1999-11-01

366

Statistical Mechanical Theory of Protein Folding in Water Environment  

NASA Astrophysics Data System (ADS)

We present a statistical mechanics formalism for the theoretical description of the process of protein folding leftrightarrow unfolding transition in water environment. The formalism is based on the construction of the partition function of a protein obeying two-stage-like folding kinetics. Using the statistical mechanics model of solvation of hydrophobic hydrocarbons we obtain the partition function of infinitely diluted solution of proteins in water environment. The calculated dependencies of the protein heat capacities upon temperature are compared with the corresponding results of experimental measurements for staphylococcal nuclease.

Yakubovich, Alexander V.; Solov'yov, Andrey V.; Greiner, Walter

367

NMR-based structural biology of proteins in supercooled water.  

PubMed

NMR-based structural biology of proteins can be pursued efficiently in supercooled water at temperatures well below the freezing point of water. This enables one to study protein structure, dynamics, hydration and cold denaturation in an unperturbed aqueous solution at very low temperatures. Furthermore, such studies enable one to accurately measure thermodynamic parameters associated with protein cold denaturation. Presently available approaches to acquire NMR data for supercooled aqueous protein solutions are surveyed, new insights obtained from such studies are summarized, and future perspectives are discussed. PMID:21533787

Szyperski, Thomas; Mills, Jeffrey L

2011-05-01

368

Cation channel formed at lipid bilayer by Cinnamomin, a new type II ribosome-inactivating protein.  

PubMed

Cinnamomin, a new type II ribosome-inactivating protein, purified from the seeds of Cinnamonum camphora is reconstituted into the membranes of planar lipid bilayer and giant liposome. The channel-forming activity of the cinnamomin is found and cation permeability of the channel is characterized by patch clamp. In an asymmetric solution system, bath 150/pipette 100 mM KCl, the unit conductance is 140+/-7 pS and the reversal potential is 10.4+/-0.6 mV, very close to the theoretical value of the K+ electrode. The results offer an interpretation for internalization of the RIP and the cytotoxicity difference between single and two chain RIP. PMID:10400291

Zhang, G P; Shi, Y L; Wang, W P; Liu, W Y

1999-09-01

369

Modelling the relative impact of rivers (Scheldt\\/Rhine\\/Seine) and Western Channel waters on the nutrient and diatoms\\/ Phaeocystis distributions in Belgian waters (Southern North Sea)  

Microsoft Academic Search

The coastal areas of the Southern North Sea (SNS) experience eutrophication problems resulting from freshwater nitrogen (N) and phosphorus (P) inputs from rivers. In particular, massive blooms of Phaeocystis colonies occur in Belgian waters. In this region, water masses result from the mixing of Western Channel (WCH) waters transported through the Straits of Dover with nutrient-rich freshwater from the Scheldt,

Geneviève Lacroix; Kevin Ruddick; Nathalie Gypens; Christiane Lancelot

2007-01-01

370

Binding of Buried Structural Water Increases the Flexibility of Proteins  

NASA Astrophysics Data System (ADS)

Water deeply buried in proteins is considered to be an integral part of the folded structure. Such structural water molecules make strong H bonds with polar groups of the surrounding protein and therefore are believed to tighten the protein matrix. Surprisingly, our computational analysis of the binding of a buried water molecule to bovine pancreatic trypsin inhibitor shows that the protein actually becomes more flexible, as revealed by an increase in the vibrational entropy. We find that this effect must be common in proteins, because the large entropic cost of immobilizing a single water molecule [-T? S = 20.6 kcal/mol (1 kcal = 4.18 kJ) for the lost translational and rotational degrees of freedom] can only be partly compensated by water-protein interactions, even when they are nearly perfect, as in the case of bovine pancreatic trypsin inhibitor (? E = -19.8 kcal/mol), leaving no room for a further decrease in entropy from protein tightening. This study illustrates the importance of considering changes in protein flexibility (which in this case favor binding by 3.5 kcal/mol) for the prediction of ligand binding affinities.

Fischer, Stefan; Verma, Chandra S.

1999-08-01

371

The elusive character of discontinuous deep-water channels: New insights from Lucia Chica channel system, offshore California  

USGS Publications Warehouse

New high-resolution autonomous underwater vehicle (AUV) seafloor images, with 1 m lateral resolution and 0.3 m vertical resolution, reveal unexpected seafloor rugosity and low-relief (<10 m), discontinuous conduits over ~70 km2. Continuous channel thalwegs were interpreted originally from lower-resolution images, but newly acquired AUV data indicate that a single sinuous channel fed a series of discontinuous lower-relief channels. These discontinuous channels were created by at least four avulsion events. Channel relief, defined as the height from the thalweg to the levee crest, controls avulsions and overall stratigraphic architecture of the depositional area. Flowstripped turbidity currents separated into and reactivated multiple channels to create a distributary pattern and developed discontinuous trains of cyclic scours and megaflutes, which may be erosional precursors to continuous channels. The diverse features now imaged in the Lucia Chica channel system (offshore California) are likely common in modern and ancient systems with similar overall morphologies, but have not been previously mapped with lower-resolution detection methods in any of these systems. ?? 2011 Geological Society of America.

Maier, K. L.; Fildani, A.; Paull, C. K.; Graham, S. A.; McHargue, T. R.; Caress, D. W.; McGann, M.

2011-01-01

372

Epithelial sodium channel inhibition by AMP-activated protein kinase in oocytes and polarized renal epithelial cells.  

PubMed

The epithelial Na(+) channel (ENaC) regulates epithelial salt and water reabsorption, processes that require significant expenditure of cellular energy. To test whether the ubiquitous metabolic sensor AMP-activated kinase (AMPK) regulates ENaC, we examined the effects of AMPK activation on amiloride-sensitive currents in Xenopus oocytes and polarized mouse collecting duct mpkCCD(c14) cells. Microinjection of oocytes expressing mouse ENaC (mENaC) with either active AMPK protein or an AMPK activator inhibited mENaC currents relative to controls as measured by two-electrode voltage-clamp studies. Similarly, pharmacological AMPK activation or overexpression of an activating AMPK mutant in mpkCCD(c14) cells inhibited amiloride-sensitive short circuit currents. Expression of a degenerin mutant beta-mENaC subunit (S518K) along with wild type alpha and gamma increased the channel open probability (P(o)) to approximately 1. However, AMPK activation inhibited currents similarly with expression of either degenerin mutant or wild type mENaC. Single channel recordings under these conditions demonstrated that neither P(o) nor channel conductance was affected by AMPK activation. Moreover, expression of a Liddle's syndrome-type beta-mENaC mutant (Y618A) greatly enhanced ENaC whole cell currents relative to wild type ENaC controls and prevented AMPK-dependent inhibition. These findings indicate that AMPK-dependent ENaC inhibition is mediated through a decrease in the number of active channels at the plasma membrane (N), presumably through enhanced Nedd4-2-dependent ENaC endocytosis. The AMPK-ENaC interaction appears to be indirect; AMPK did not bind ENaC in cells, as assessed by in vivo pull-down assays, nor did it phosphorylate ENaC in vitro. In summary, these results suggest a novel mechanism for coupling ENaC activity and renal Na(+) handling to cellular metabolic status through AMPK, which may help prevent cellular Na(+) loading under hypoxic or ischemic conditions. PMID:15753079

Carattino, Marcelo D; Edinger, Robert S; Grieser, Heather J; Wise, Rosalee; Neumann, Dietbert; Schlattner, Uwe; Johnson, John P; Kleyman, Thomas R; Hallows, Kenneth R

2005-03-07

373

TRPC1 protein forms only one type of native store-operated channels in HEK293 cells.  

PubMed

TRPC1 is a major component of store-operated calcium entry in many cell types. In our previous studies, three types of endogenous store-operated calcium channels have been described in HEK293 cells, but it remained unknown which of these channels are composed of TRPC1 proteins. Here, this issue has been addressed by performing single-channel analysis in HEK293 cells transfected with anti-TRPC1 siRNA (siTPRC1) or a TPRC1-encoding plasmid. The results show that thapsigargin-or agonist-induced calcium influx is significantly attenuated in siTRPC1-transfected HEK293 cells. TRPC1 knockdown by siRNA results in the disappearance of store-operated I(max) channels, while the properties of I(min) and I(NS) channels are unaffected. In HEK293 cells with overexpressed TRPC1 protein, the unitary current-voltage relationship of exogenous TRPC1 channels is almost linear, with a slope conductance of about 17 pS. The extrapolated reversal potential of expressed TRPC1 channels is +30 mV. Therefore, the main electrophysiological and regulatory properties of expressed TRPC1 and native I(max) channels are identical. Moreover, TRPC1 overexpression in HEK293 cells results in an increased number of store-operated I(max) channels. All these data allow us to conclude that TRPC1 protein forms native store-operated I(max) channels but is not an essential subunit for other store-operated channel types in HEK293 cells. PMID:23079337

Skopin, Anton; Shalygin, Alexey; Vigont, Vladimir; Zimina, Olga; Glushankova, Lyubov; Mozhayeva, Galina N; Kaznacheyeva, Elena

2012-10-16

374

Water Induced Effects on the Thermal Response of a Protein  

NASA Astrophysics Data System (ADS)

A model protein and surrounding water have been investigated at different temperatures. We have detected an anomalous compression of the protein near the freezing point of water—a compression not obviously related to the negative thermal expansion of the solvent. Moreover, the physiological protein working temperature (T=300 K) appears to be related to the activation of exchange of vicinal water with the bulk and the concomitant absorption of heat by hydrophilic amino acids. The inferred activation was interpreted on the basis of degenerate tetrahedral order between the hydration shell and the bulk. The results support the notion that the dynamics of vicinal water makes a substantial contribution to the activity optimum of proteins.

Melchionna, Simone; Briganti, Giuseppe; Londei, Paola; Cammarano, Piero

2004-04-01

375

Water-mediated ionic interactions in protein structures.  

PubMed

It is well known that water molecules play an indispensable role in the structure and function of biological macromolecules. The water-mediated ionic interactions between the charged residues provide stability and plasticity and in turn address the function of the protein structures. Thus, this study specifically addresses the number of possible water-mediated ionic interactions, their occurrence, distribution and nature found in 90% non-redundant protein chains. Further, it provides a statistical report of different charged residue pairs that are mediated by surface or buried water molecules to form the interactions. Also, it discusses its contributions in stabilizing various secondary structural elements of the protein. Thus, the present study shows the ubiquitous nature of the interactions that imparts plasticity and flexibility to a protein molecule. PMID:21654080

Sabarinathan, R; Aishwarya, K; Sarani, R; Vaishnavi, M Kirti; Sekar, K

2011-06-01

376

Water circulation in non-isothermal droplet-laden turbulent channel flow  

NASA Astrophysics Data System (ADS)

We propose a point-particle model for two-way coupling of water droplets dispersed in turbulent flow of a carrier gas consisting of air and water vapor. An incompressible flow formulation is applied for direct numerical simulation (DNS) of turbulent channel flow with a warm and a cold wall. Compared to simulations without droplets or with solid particles a significant increase in Nusselt number is found, arising from the additional phase changes. In the statistically steady state, which is reached after a long time, the flow exhibits a mean motion of water vapor from the warm wall to the cold wall. Vapor condenses on average on drops near the cold wall and evaporates from drops near the warm wall. This transport is balanced by a net mean mass transfer of droplets from the cold wall to the warm wall.

Russo, E.; Kuerten, J. G. M.; van der Geld, C. W. M.; Geurts, B. J.

2013-10-01

377

Communication: Protein dynamical transition vs. liquid-liquid phase transition in protein hydration water  

NASA Astrophysics Data System (ADS)

In this work, we compare experimental data on myoglobin hydrated powders from elastic neutron scattering, broadband dielectric spectroscopy, and differential scanning calorimetry. Our aim is to obtain new insights on the connection between the protein dynamical transition, a fundamental phenomenon observed in proteins whose physical origin is highly debated, and the liquid-liquid phase transition (LLPT) possibly occurring in protein hydration water and related to the existence of a low temperature critical point in supercooled water. Our results provide a consistent thermodynamic/dynamic description which gives experimental support to the LLPT hypothesis and further reveals how fundamental properties of water and proteins are tightly related.

Schirò, Giorgio; Fomina, Margarita; Cupane, Antonio

2013-09-01

378

Channel Surface Patterning of Alternating Biomimetic Protein Combinations for Enhanced Microfluidic Tumor Cell Isolation  

PubMed Central

Here we report a new method for multi-component protein patterning in a microchannel and also a technique for improving immunoaffinity-based circulating tumor cell (CTC) capture by patterning regions of alternating adhesive proteins using the new method. The first of two proteins, anti-epithelial cell adhesion molecule (anti-EpCAM), provides the specificity for CTC capture. The second, E-selectin, increases CTC capture under shear. Patterning regions with and without E-selectin allows captured leukocytes, which also bind E-selectin and are unwanted impurities in CTC isolation, to roll a short distance and detach from the capture surface. This reduces leukocyte capture by up to 82%. The patterning is combined with a leukocyte elution step in which a calcium chelating buffer effectively deactivates E-selectin so that leukocytes may be rinsed away 60% more efficiently than with a buffer containing calcium. The alternating patterning of this biomimetic protein combination, used in conjunction with the elution step, reduce capture of leukocytes while maintaining a high tumor capture efficiency that is up to 1.9 times higher than the tumor cell capture efficiency of a surface with only anti-EpCAM. The new patterning technique described here does not require mask alignment and can be used to spatially control the immobilization of any 2 proteins or protein mixtures inside a sealed microfluidic channel.

Launiere, Cari; Gaskill, Marissa; Czaplewski, Gregory; Myung, Ja Hye; Hong, Seungpyo; Eddington, David T.

2012-01-01

379

Regulation of Ca2+ channel expression at the cell surface by the small G-protein kir/Gem.  

PubMed

Voltage-dependent calcium (Ca2+) channels are involved in many specialized cellular functions, and are controlled by intracellular signals such as heterotrimeric G-proteins, protein kinases and calmodulin (CaM). However, the direct role of small G-proteins in the regulation of Ca2+ channels is unclear. We report here that the GTP-bound form of kir/Gem, identified originally as a Ras-related small G-protein that binds CaM, inhibits high-voltage-activated Ca2+ channel activities by interacting directly with the beta-subunit. The reduced channel activities are due to a decrease in alpha1-subunit expression at the plasma membrane. The binding of Ca2+/CaM to kir/Gem is required for this inhibitory effect by promoting the cytoplasmic localization of kir/Gem. Inhibition of L-type Ca2+ channels by kir/Gem prevents Ca2+-triggered exocytosis in hormone-secreting cells. We propose that the small G-protein kir/Gem, interacting with beta-subunits, regulates Ca2+ channel expression at the cell surface. PMID:11395774

Béguin, P; Nagashima, K; Gonoi, T; Shibasaki, T; Takahashi, K; Kashima, Y; Ozaki, N; Geering, K; Iwanaga, T; Seino, S

2001-06-01

380

Gbetagamma-dependent and Gbetagamma-independent basal activity of G protein-activated K+ channels.  

PubMed

Cardiac and neuronal G protein-activated K+ channels (GIRK; Kir3) open following the binding of Gbetagamma subunits, released from Gi/o proteins activated by neurotransmitters. GIRKs also possess basal activity contributing to the resting potential in neurons. It appears to depend largely on free Gbetagamma, but a Gbetagamma-independent component has also been envisaged. We investigated Gbetagamma dependence of the basal GIRK activity (A(GIRK,basal)) quantitatively, by titrated expression of Gbetagamma scavengers, in Xenopus oocytes expressing GIRK1/2 channels and muscarinic m2 receptors. The widely used Gbetagamma scavenger, myristoylated C terminus of beta-adrenergic kinase (m-cbetaARK), reduced A(GIRK,basal) by 70-80% and eliminated the acetylcholine-evoked current (I(ACh)). However, we found that m-cbetaARK directly binds to GIRK, complicating the interpretation of physiological data. Among several newly constructed Gbetagamma scavengers, phosducin with an added myristoylation signal (m-phosducin) was most efficient in reducing GIRK currents. m-phosducin relocated to the membrane fraction and did not bind GIRK. Titrated expression of m-phosducin caused a reduction of A(GIRK,basal) by up to 90%. Expression of GIRK was accompanied by an increase in the level of Gbetagamma and Galpha in the plasma membrane, supporting the existence of preformed complexes of GIRK with G protein subunits. Increased expression of Gbetagamma and its constitutive association with GIRK may underlie the excessively high A(GIRK,basal) observed at high expression levels of GIRK. Only 10-15% of A(GIRK,basal) persisted upon expression of both m-phosducin and cbetaARK. These results demonstrate that a major part of Ibasal is Gbetagamma-dependent at all levels of channel expression, and only a small fraction (<10%) may be Gbetagamma-independent. PMID:15728579

Rishal, Ida; Porozov, Yuri; Yakubovich, Daniel; Varon, Dalia; Dascal, Nathan

2005-02-23

381

Paramagnetic Cu(II) For Probing Membrane Protein Structure and Function: Inhibition Mechanism of the Influenza M2 Proton Channel  

PubMed Central

Paramagnetic Cu(II) ions enhance nuclear spin relaxation in a distance-dependent fashion and can be used as a structural probe of proteins. Cu(II) can also serve as functionally important ligands in proteins. Here we investigate the structural basis of Cu(II) inhibition of the influenza M2 proton channel through Cu(II)-induced paramagnetic relaxation enhancement (PRE). 13C T1 relaxation rates of the central residues of the transmembrane (TM) domain of M2 are significantly enhanced by Cu(II), and pronounced spectral broadening is observed for the proton-selective residue, His37. These data yielded quantitative distances of 13C spins to the Cu(II) center, and identified the Cu(II) binding site to be N?2 of His37. This binding site is surrounded by four imidazole rings from the top and four indole rings of Trp41 from the bottom, thus explaining the high affinity of Cu(II) binding. Bound at this location, Cu(II) can inhibit proton currents by perturbing histidine-water proton exchange, preventing histidine conformational dynamics, and interfering with His-Trp cation-? interaction. The Cu(II) binding site is distinct from the binding site of the hydrophobic drug amantadine, which is about 10 Å N-terminal to His37. Consistently, Cu(II) and amantadine induce distinct conformational changes at several key residues, suggesting the possibility of designing new drugs that target the His37 site to inhibit amantadine-resistant mutant M2 proteins. In addition to the high-affinity His37 binding site, we also examined the weaker and non-specific binding of Cu(II) to membrane-surface lipid phosphates and the extent of the resulting PRE to surface-proximal protein residues. This study demonstrates the feasibility of NMR studies of paramagnetic-ion complexed membrane proteins, where the ion serves as both a functional ligand and a distance probe.

Su, Yongchao; Hu, Fanghao; Hong, Mei

2012-01-01

382

Paramagnetic Cu(II) for probing membrane protein structure and function: inhibition mechanism of the influenza M2 proton channel.  

PubMed

Paramagnetic Cu(II) ions enhance nuclear spin relaxation in a distance-dependent fashion and can be used as a structural probe of proteins. Cu(II) can also serve as a functionally important ligand in proteins. Here we investigate the structural basis of Cu(II) inhibition of the influenza M2 proton channel through Cu(II)-induced paramagnetic relaxation enhancement (PRE). (13)C T(1) relaxation rates of the central residues of the transmembrane (TM) domain of M2 are significantly enhanced by Cu(II), and pronounced spectral broadening is observed for the proton-selective residue, His37. These data yielded quantitative distances of (13)C spins to the Cu(II) center and identified the Cu(II) binding site to be N?2 of His37. This binding site is surrounded by four imidazole rings from the top and four indole rings of Trp41 from the bottom, thus explaining the high affinity of Cu(II) binding. Bound at this location, Cu(II) can inhibit proton currents by perturbing histidine-water proton exchange, preventing histidine conformational dynamics, and interfering with His-Trp cation-? interaction. The Cu(II) binding site is distinct from the binding site of the hydrophobic drug amantadine, which is about 10 Å N-terminal to His37. Consistently, Cu(II) and amantadine induce distinct conformational changes at several key residues, suggesting the possibility of designing new drugs that target the His37 site to inhibit amantadine-resistant mutant M2 proteins. In addition to the high-affinity His37 binding site, we also examined the weaker and nonspecific binding of Cu(II) to membrane-surface lipid phosphates and the extent of the resulting PRE to surface-proximal protein residues. This study demonstrates the feasibility of NMR studies of paramagnetic-ion-complexed membrane proteins, where the ion serves as both a functional ligand and a distance probe. PMID:22519936

Su, Yongchao; Hu, Fanghao; Hong, Mei

2012-05-08

383

Infiltration and quality of water for two arroyo channels, Albuquerque, New Mexico, 1988-92  

USGS Publications Warehouse

Selected reaches of Grant Line Arroyo and Tijeras Arroyo in Albuquerque, New Mexico, were studied to collect information about the amount and quality of infiltration through arroyo channels. Infiltration rate was calculated for selected reaches of Grant Line Arroyo and Tijeras Arroyo based on instantaneous streamflow-loss volumes, wetted channel area, and instantaneous evaporation rates measured during 1988-92. Infiltration rates at Grant Line Arroyo ranged from 0.0 to 0.6 foot per day, and at Tijeras Arroyo from 2.28 to 30 feet per day. The evaporation rate ranged from one-tenth of 1 percent to 2 percent of the infiltration rate. Infiltration rates differed with the location of the reach isolated for measurement and with the time of day of the infiltration-rate measurement. Differences in intrinsic permeability of the sediments may be the most important factor affecting spatial variations in infiltration. The most important factor affecting temporal variations in infiltration may be the temperature of the water and sediment where infiltration occurs. Annual evaporation rates were greatest over saturated stream sediments and ranged from 802 to 1,025 millimeters per year or from 31.57 to 40.35 inches per year. Annual evaporation rates were least over unsaturated, unvegetated soil and ranged from 174 to 291 millimeters per year or from 6.85 to 11.46 inches per year. Annual evapotranspiration rates over grasses or shrubs or both were about one-half the rates over saturated stream sediments. Rates were similar for Grant Line and Tijeras Arroyos. The land- surface vegetation, availability of water at the land surface, availability of energy to enable a change of state from water to vapor, existence of a vapor concentration gradient, and a turbulent atmosphere to carry the vapor away may be the factors that determine the amount of evaporation and evapotranspiration. Water in Grant Line Arroyo and Tijeras Arroyo met U. S. Environmental Protection Agency drinking-water regulations for nitrate, volatile organic compounds, dissolved lead, and dissolved and total arsenic, barium, cadmium, chromium, copper, iron, silver, zinc, selenium, chloride, and sulfate concentrations. Total lead concentration in one sample from Tramway Floodway Channel, a tributary to Tijeras Arroyo, was 55 micrograms per liter, exceeding the Environmental Protection Agency drinking-water regulation of 50 micrograms per liter. Dissolved-solids concentrations calculated from the sum of cations and anions usually exceeded the Environmental Protection Agency drinking-water dissolved-solids regulation of 500 milligrams per liter at Tijeras Arroyo above Four Hills Bridge.

Thomas, Carole L.

1995-01-01

384

Monocyte Chemotactic Protein1 Regulates Voltage-Gated K + Channels and Macrophage Transmigration  

Microsoft Academic Search

Progressive human immunodeficiency virus (HIV)-1 infection and virus-induced neuroinflammatory responses effectuate monocyte-macrophage\\u000a transmigration across the blood–brain barrier (BBB). A key factor in mediating these events is monocyte chemotactic protein-1\\u000a (MCP-1). Upregulated glial-derived MCP-1 in HIV-1-infected brain tissues generates a gradient for monocyte recruitment into\\u000a the nervous system. We posit that the inter-relationships between MCP-1, voltage-gated ion channels, cell shape and

Howard E. Gendelman; Shengyuan Ding; Nan Gong; Jianuo Liu; Servio H. Ramirez; Yuri Persidsky; R. Lee Mosley; Tong Wang; David J. Volsky; Huangui Xiong

2009-01-01

385

Concerted action of two cation filters in the aquaporin water channel  

PubMed Central

Aquaporin (AQP) facilitated water transport is common to virtually all cell membranes and is marked by almost perfect specificity and high flux rates. Simultaneously, protons and cations are strictly excluded to maintain ionic transmembrane gradients. Yet, the AQP cation filters have not been identified experimentally. We report that three point mutations turned the water-specific AQP1 into a proton/alkali cation channel with reduced water permeability and the permeability sequence: H+ ?K+ >Rb+ >Na+ >Cs+ >Li+. Contrary to theoretical models, we found that electrostatic repulsion at the central asn-pro-ala (NPA) region does not suffice to exclude protons. Full proton exclusion is reached only in conjunction with the aromatic/arginine (ar/R) constriction at the pore mouth. In contrast, alkali cations are blocked by the NPA region but leak through the ar/R constriction. Expression of alkali-leaking AQPs depolarized membrane potentials and compromised cell survival. Our results hint at the alkali-tight but solute-unselective NPA region as a feature of primordial channels and the proton-tight and solute-selective ar/R constriction variants as later adaptations within the AQP superfamily.

Wu, Binghua; Steinbronn, Christina; Alsterfjord, Magnus; Zeuthen, Thomas; Beitz, Eric

2009-01-01

386

Energetics of the protein-DNA-water interaction  

Microsoft Academic Search

BACKGROUND: To understand the energetics of the interaction between protein and DNA we analyzed 39 crystallographically characterized complexes with the HINT (Hydropathic INTeractions) computational model. HINT is an empirical free energy force field based on solvent partitioning of small molecules between water and 1-octanol. Our previous studies on protein-ligand complexes demonstrated that free energy predictions were significantly improved by taking

Francesca Spyrakis; Pietro Cozzini; Chiara Bertoli; Anna Marabotti; Glen E Kellogg; Andrea Mozzarelli

2007-01-01

387

[On the methods of calculation of the electrostatic potential in a protein channel].  

PubMed

The profiles of the electrostatic potential along the axis of a gramicidin channel were calculated using two quantum chemistry methods (EHT and CNDO/2) and three methods of force fields (AMBER, CHARMM, and OPLS). The calculations were performed without taking into account the contribution of water. A comparative analysis of the calculated profiles indicated that the electrostatic field of point charges of the CHARMM force field is close to that obtained by the quantum chemistry methods. It was concluded that there is no need to calculate the electric field using laborious quantum-mechanical methods since the less laborious method of the CHARMM force field gives approximately the same results. PMID:15327210

Dmitriev, A V; Tverdislov, V A

388

Adhesive water networks facilitate binding of protein interfaces  

Microsoft Academic Search

Water structure has an essential role in biological assembly. Hydrophobic dewetting has been documented as a general mechanism for the assembly of hydrophobic surfaces; however, the association mechanism of hydrophilic interfaces remains mysterious and cannot be explained by simple continuum water models that ignore the solvent structure. Here we study the association of two hydrophilic proteins using unbiased extensive molecular

Mazen Ahmad; Wei Gu; Tihamér Geyer; Volkhard Helms

2011-01-01

389

INFLUENCE OF ICE SURFACE EMISSIVITYVARIATIONS ON THE ACCURACY OF WATER VAPOR RETRIEVAL IN POLAR REGIONS USINGAMSU-B CHANNELS  

Microsoft Academic Search

Atmospheric water vapor is essential in meteorological and environmental studies. Till now, integrated water vapor content retrieval can only be operational done over oceans from microwave sensor measurements. Over land water vapor retrieval scheme is still explored. In 1998, J. Miao proposed a method to retrieve the integrated water vapor (IWV) using SSM\\/T2 and AMSU-B channels over the ice covered

Mu Qiao; Jungang Miao

390

Calmodulin and S100A1 Protein Interact with N Terminus of TRPM3 Channel*  

PubMed Central

Transient receptor potential melastatin 3 ion channel (TRPM3) belongs to the TRP family of cation-permeable ion channels involved in many important biological functions such as pain transduction, thermosensation, and mechanoregulation. The channel was reported to play an important role in Ca2+ homeostasis, but its gating mechanisms, functions, and regulation are still under research. Utilizing biophysical and biochemical methods, we characterized two independent domains, Ala-35–Lys-124 and His-291–Gly-382, on the TRPM3 N terminus, responsible for interactions with the Ca2+-binding proteins calmodulin (CaM) and S100A1. We identified several positively charged residues within these domains as having a crucial impact on CaM/S100A1 binding. The data also suggest that the interaction is calcium-dependent. We also performed competition assays, which suggested that CaM and S100A1 are able to compete for the same binding sites within the TRPM3 N terminus. This is the first time that such an interaction has been shown for TRP family members.

Holakovska, Blanka; Grycova, Lenka; Jirku, Michaela; Sulc, Miroslav; Bumba, Ladislav; Teisinger, Jan

2012-01-01

391

Water Dynamics and Dewetting Transitions in the Small Mechanosensitive Channel MscS  

PubMed Central

The dynamics of confined water in capillaries and nanotubes suggests that gating of ion channels may involve not only changes of the pore geometry, but also transitions between water-filled and empty states in certain locations. The recently solved heptameric structure of the small mechanosensitive channel of Escherichia coli, MscS, has revealed a relatively wide (7–15 Å) yet highly hydrophobic transmembrane pore. Continuum estimations based on the properties of pore surface suggest low conductance and a thermodynamic possibility of dewetting. To test the predictions we performed molecular dynamics simulations of MscS filled with flexible TIP3P water. Irrespective to the initial conditions, several independent 6-ns simulations converged to the same stable state with the pore water-filled in the wider part, but predominantly empty in the narrow hydrophobic part, displaying intermittent vapor-liquid transitions. The polar gain-of-function substitution L109S in the constriction resulted in a stable hydration of the entire pore. Steered passages of Cl? ions through the narrow part of the pore consistently produced partial ion dehydration and required a force of 200–400 pN to overcome an estimated barrier of 10–20 kcal/mole, implying negligibly low conductance. We conclude that the crystal structure of MscS does not represent an open state. We infer that MscS gate, which is similar to that of the nicotinic ACh receptor, involves a vapor-lock mechanism where limited changes of geometry or surface polarity can locally switch the regime between water-filled (conducting) and empty (nonconducting) states.

Anishkin, Andriy; Sukharev, Sergei

2004-01-01

392

Convergent and Parallel Activation of Low-Conductance Potassium Channels by Calcium and cAMP-Dependent Protein Kinase  

NASA Astrophysics Data System (ADS)

K^+ channels, which have been linked to regulation of electrogenic solute transport as well as Ca2+ influx, represent a locus in hepatocytes for the concerted actions of hormones that employ Ca2+ and cAMP as intracellular messengers. Despite considerable study, the single-channel basis for synergistic effects of Ca2+ and cAMP on hepatocellular K^+ conductance is not well understood. To address this question, patch-clamp recording techniques were applied to a model liver cell line, HTC hepatoma cells. Increasing the cytosolic Ca2+ concentration ([Ca2+]_i) in HTC cells, either by activation of purinergic receptors with ATP or by inhibition of intracellular Ca2+ sequestration with thapsigargin, activated low-conductance (9-pS) K^+ channels. Studies with excised membrane patches suggested that these channels were directly activated by Ca2+. Exposure of HTC cells to a permeant cAMP analog, 8-(4-chlorophenylthio)-cAMP, also activated 9-pS K^+ channels but did not change[Ca2+]_i. In excised membrane patches, cAMP-dependent protein kinase (the downstream effector of cAMP) activated K^+ channels with conductance and selectivity identical to those of channels activated by Ca2+. In addition, cAMP-dependent protein kinase activated a distinct K^+ channel type (5 pS). These data represent the differential regulation of low-conductance K^+ channels by signaling pathways mediated by Ca2+ and cAMP. Moreover, since low-conductance Ca2+ -activated K^+ channels have been identified in a variety of cell types, these findings suggest that differential regulation of K^+ channels by hormones with distinct signaling pathways may provide a mechanism for hormonal control of solute transport and Ca2+-dependent cellular functions in the liver as well as other nonexcitable tissues.

Lidofsky, Steven D.

1995-07-01

393

AMP-activated protein kinase regulates hERG potassium channel.  

PubMed

Besides their role in cardiac repolarization, human ether-a-go-go-related gene potassium (hERG) channels are expressed in several tumor cells including rhabdomyosarcoma cells. The channels foster cell proliferation. Ubiquitously expressed AMP-dependent protein kinase (AMPK) is a serine-/threonine kinase, stimulating energy-generating and inhibiting energy-consuming processes thereby helping cells survive periods of energy depletion. AMPK has previously been shown to regulate Na(+)/K(+) ATPase, Na(+)/Ca(2+) exchangers, Ca(2+) channels and K(+) channels. The present study tested whether AMPK regulates hERG channel activity. Wild type AMPK (?1?1?1), constitutively active (?R70Q)AMPK (?1?1?1(R70Q)), or catalytically inactive (?K45R)AMPK (?1(K45R)?1?1) were expressed in Xenopus oocytes with hERG. Tail currents were determined as a measure of hERG channel activity by two-electrode-voltage clamp. hERG membrane abundance was quantified by chemiluminescence and visualized by immunocytochemistry and confocal microscopy. Moreover, hERG currents were measured in RD rhabdomyosarcoma cells after pharmacological modification of AMPK activity using the patch clamp technique. Coexpression of wild-type AMPK and of constitutively active (?R70Q)AMPK significantly downregulated the tail currents in hERG-expressing Xenopus oocytes. Pharmacological activation of AMPK with AICAR or with phenformin inhibited hERG currents in Xenopus oocytes, an effect abrogated by AMPK inhibitor compound C. (?R70Q)AMPK enhanced the Nedd4-2-dependent downregulation of hERG currents. Coexpression of constitutively active (?R70Q)AMPK decreased membrane expression of hERG in Xenopus oocytes. Compound C significantly enhanced whereas AICAR tended to inhibit hERG currents in RD rhabdomyosarcoma cells. AMPK is a powerful regulator of hERG-mediated currents in both, Xenopus oocytes and RD rhabdomyosarcoma cells. AMPK-dependent regulation of hERG may be particularly relevant in cardiac hypertrophy and tumor growth. PMID:23716168

Almilaji, Ahmad; Munoz, Carlos; Elvira, Bernat; Fajol, Abul; Pakladok, Tatsiana; Honisch, Sabina; Shumilina, Ekaterina; Lang, Florian; Föller, Michael

2013-05-29

394

Molecular understanding of sterically controlled compound release through an engineered channel protein (FhuA)  

PubMed Central

Background Recently we reported a nanocontainer based reduction triggered release system through an engineered transmembrane channel (FhuA ?1-160; Onaca et al., 2008). Compound fluxes within the FhuA ?1-160 channel protein are controlled sterically through labeled lysine residues (label: 3-(2-pyridyldithio)propionic-acid-N-hydroxysuccinimide-ester). Quantifying the sterical contribution of each labeled lysine would open up an opportunity for designing compound specific drug release systems. Results In total, 12 FhuA ?1-160 variants were generated to gain insights on sterically controlled compound fluxes: Subset A) six FhuA ?1-160 variants in which one of the six lysines in the interior of FhuA ?1-160 was substituted to alanine and Subset B) six FhuA ?1-160 variants in which only one lysine inside the barrel was not changed to alanine. Translocation efficiencies were quantified with the colorimetric TMB (3,3',5,5'-tetramethylbenzidine) detection system employing horseradish peroxidase (HRP). Investigation of the six subset A variants identified position K556A as sterically important. The K556A substitution increases TMB diffusion from 15 to 97 [nM]/s and reaches nearly the TMB diffusion value of the unlabeled FhuA ?1-160 (102 [nM]/s). The prominent role of position K556 is confirmed by the corresponding subset B variant which contains only the K556 lysine in the interior of the barrel. Pyridyl labeling of K556 reduces TMB translocation to 16 [nM]/s reaching nearly background levels in liposomes (13 [nM]/s). A first B-factor analysis based on MD simulations confirmed that position K556 is the least fluctuating lysine among the six in the channel interior of FhuA ?1-160 and therefore well suited for controlling compound fluxes through steric hindrance. Conclusions A FhuA ?1-160 based reduction triggered release system has been shown to control the compound flux by the presence of only one inner channel sterical hindrance based on 3-(2-pyridyldithio)propionic-acid labeling (amino acid position K556). As a consequence, the release kinetic can be modulated by introducing an opportune number of hindrances. The FhuA ?1-160 channel embedded in liposomes can be advanced to a universal and compound independent release system which allows a size selective compound release through rationally re-engineered channels.

2010-01-01

395

Aquaporin11: A channel protein lacking apparent transport function expressed in brain  

Microsoft Academic Search

BACKGROUND: The aquaporins are a family of integral membrane proteins composed of two subfamilies: the orthodox aquaporins, which transport only water, and the aquaglyceroporins, which transport glycerol, urea, or other small solutes. Two recently described aquaporins, numbers 11 and 12, appear to be more distantly related to the other mammalian aquaporins and aquaglyceroporins. RESULTS: We report on the characterization of

Daniel A Gorelick; Jeppe Praetorius; Takashi Tsunenari; Søren Nielsen; Peter Agre

2006-01-01

396

Two-channel microwave radiometer for observations of total column precipitable water vapor and cloud liquid water path  

SciTech Connect

The Atmospheric Radiation Measurement (ARM) Program is focused on improving the treatment of radiation transfer in models of the atmospheric general circulation, as well as on improving parameterizations of cloud properties and formation processes in these models (USDOE, 1990). To help achieve these objectives, ARM is deploying several two-channel, microwave radiometers at the Cloud and Radiation Testbed (CART) site in Oklahoma for the purpose of obtaining long time series observations of total precipitable water vapor (PWV) and cloud liquid water path (LWP). The performance of the WVR-1100 microwave radiometer deployed by ARM at the Oklahoma CART site central facility to provide time series measurements precipitable water vapor (PWV) and liquid water path (LWP) has been presented. The instrument has proven to be durable and reliable in continuous field operation since June, 1992. The accuracy of the PWV has been demonstrated to achieve the limiting accuracy of the statistical retrieval under clear sky conditions, degrading with increasing LWP. Improvements are planned to address moisture accumulation on the Teflon window, as well as to identity the presence of clouds with LWP at or below the retrieval uncertainty.

Liljegren, J.C.

1994-01-01

397

Bound Water at Protein-Protein Interfaces: Partners, Roles and Hydrophobic Bubbles as a Conserved Motif  

Microsoft Academic Search

BackgroundThere is a great interest in understanding and exploiting protein-protein associations as new routes for treating human disease. However, these associations are difficult to structurally characterize or model although the number of X-ray structures for protein-protein complexes is expanding. One feature of these complexes that has received little attention is the role of water molecules in the interfacial region.MethodologyA data

Mostafa H. Ahmed; Francesca Spyrakis; Pietro Cozzini; Parijat K. Tripathi; Andrea Mozzarelli; J. Neel Scarsdale; Martin A. Safo; Glen E. Kellogg

2011-01-01

398

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