scholarly journals Genetic Diversity of Potassium Ion Channel Proteins Encoded by Chloroviruses That Infect Chlorella heliozoae

Viruses ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 678
Author(s):  
Carter R. Murry ◽  
Irina V. Agarkova ◽  
Jayadri S. Ghosh ◽  
Fiona C. Fitzgerald ◽  
Roger M. Carlson ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Amino Acids ◽  
Dna Sequences ◽  
Transmembrane Domain ◽  
Potassium Ion ◽  
K Channel ◽  
K Channels ◽  
Large Plaque ◽  
Channel Proteins ◽  
Dsdna Viruses

Chloroviruses are large, plaque-forming, dsDNA viruses that infect chlorella-like green algae that live in a symbiotic relationship with protists. Chloroviruses have genomes from 290 to 370 kb, and they encode as many as 400 proteins. One interesting feature of chloroviruses is that they encode a potassium ion (K+) channel protein named Kcv. The Kcv protein encoded by SAG chlorovirus ATCV-1 is one of the smallest known functional K+ channel proteins consisting of 82 amino acids. The KcvATCV-1 protein has similarities to the family of two transmembrane domain K+ channel proteins; it consists of two transmembrane α-helixes with a pore region in the middle, making it an ideal model for studying K+ channels. To assess their genetic diversity, kcv genes were sequenced from 103 geographically distinct SAG chlorovirus isolates. Of the 103 kcv genes, there were 42 unique DNA sequences that translated into 26 new Kcv channels. The new predicted Kcv proteins differed from KcvATCV-1 by 1 to 55 amino acids. The most conserved region of the Kcv protein was the filter, the turret and the pore helix were fairly well conserved, and the outer and the inner transmembrane domains of the protein were the most variable. Two of the new predicted channels were shown to be functional K+ channels.

scholarly journals Membrane-delimited Inhibition of Maxi-K Channel Activity by the Intermediate Conductance Ca2+-activated K Channel

2006 ◽  
Vol 127 (2) ◽  
pp. 159-169 ◽  
Author(s):  
Jill Thompson ◽  
Ted Begenisich
Keyword(s):  
Single Channel ◽  
Expression System ◽  
Chemical Activation ◽  
K Channel ◽  
Channel Activity ◽  
Single Family ◽  
Open Probability ◽  
K Channels ◽  
Channel Proteins ◽  
K Activity

The complexity of mammalian physiology requires a diverse array of ion channel proteins. This diversity extends even to a single family of channels. For example, the family of Ca2+-activated K channels contains three structural subfamilies characterized by small, intermediate, and large single channel conductances. Many cells and tissues, including neurons, vascular smooth muscle, endothelial cells, macrophages, and salivary glands express more than a single class of these channels, raising questions about their specific physiological roles. We demonstrate here a novel interaction between two types of Ca2+-activated K channels: maxi-K channels, encoded by the KCa1.1 gene, and IK1 channels (KCa3.1). In both native parotid acinar cells and in a heterologous expression system, activation of IK1 channels inhibits maxi-K activity. This interaction was independent of the mode of activation of the IK1 channels: direct application of Ca2+, muscarinic receptor stimulation, or by direct chemical activation of the IK1 channels. The IK1-induced inhibition of maxi-K activity occurred in small, cell-free membrane patches and was due to a reduction in the maxi-K channel open probability and not to a change in the single channel current level. These data suggest that IK1 channels inhibit maxi-K channel activity via a direct, membrane-delimited interaction between the channel proteins. A quantitative analysis indicates that each maxi-K channel may be surrounded by four IK1 channels and will be inhibited if any one of these IK1 channels opens. This novel, regulated inhibition of maxi-K channels by activation of IK1 adds to the complexity of the properties of these Ca2+-activated K channels and likely contributes to the diversity of their functional roles.

A Transmembrane Domain of the Sulfonylurea Receptor Mediates Activation of ATP-Sensitive K+ Channels by K+Channel Openers

1999 ◽  
Vol 56 (2) ◽  
pp. 308-315 ◽  
Author(s):  
Nathalie D’hahan ◽  
Hélène Jacquet ◽  
Christophe Moreau ◽  
Patrice Catty ◽  
Michel Vivaudou
Keyword(s):  
Transmembrane Domain ◽  
K Channel ◽  
Sulfonylurea Receptor ◽  
K Channels

scholarly journals KCNE3 Truncation Mutants Reveal a Bipartite Modulation of KCNQ1 K+ Channels

2004 ◽  
Vol 124 (6) ◽  
pp. 759-771 ◽  
Author(s):  
Steven D. Gage ◽  
William R. Kobertz
Keyword(s):  
Amino Acids ◽  
Transmembrane Domain ◽  
Channel Gating ◽  
Terminal Region ◽  
Type I ◽  
Long Qt ◽  
Transmembrane Peptides ◽  
K Channels ◽  
Voltage Gated ◽  
La Luna

The five KCNE genes encode a family of type I transmembrane peptides that assemble with KCNQ1 and other voltage-gated K+ channels, resulting in potassium conducting complexes with varied channel-gating properties. It has been recently proposed that a triplet of amino acids within the transmembrane domain of KCNE1 and KCNE3 confers modulation specificity to the peptide, since swapping of these three residues essentially converts the recipient KCNE into the donor (Melman, Y.F., A. Domenech, S. de la Luna, and T.V. McDonald. 2001. J. Biol. Chem. 276:6439–6444). However, these results are in stark contrast with earlier KCNE1 deletion studies, which demonstrated that a COOH-terminal region, highly conserved between KCNE1 and KCNE3, was responsible for KCNE1 modulation of KCNQ1 (Tapper, A.R., and A.L. George. 2000 J. Gen. Physiol. 116:379–389.). To ascertain whether KCNE3 peptides behave similarly to KCNE1, we examined a panel of NH2- and COOH-terminal KCNE3 truncation mutants to directly determine the regions required for assembly with and modulation of KCNQ1 channels. Truncations lacking the majority of their NH2 terminus, COOH terminus, or mutants harboring both truncations gave rise to KCNQ1 channel complexes with basal activation, a hallmark of KCNE3 modulation. These results demonstrate that the KCNE3 transmembrane domain is sufficient for assembly with and modulation of KCNQ1 channels and suggests a bipartite model for KCNQ1 modulation by KCNE1 and KCNE3 subunits. In this model, the KCNE3 transmembrane domain is active in modulation and overrides the COOH terminus' contribution, whereas the KCNE1 transmembrane domain is passive and reveals COOH-terminal modulation of KCNQ1 channels. We furthermore test the validity of this model by using the active KCNE3 transmembrane domain to functionally rescue a nonconducting, yet assembly and trafficking competent, long QT mutation located in the conserved COOH-terminal region of KCNE1.

scholarly journals Identification of a cytoplasmic domain important in the polarized expression and clustering of the Kv2.1 K+ channel.

1996 ◽  
Vol 135 (6) ◽  
pp. 1619-1632 ◽  
Author(s):  
R H Scannevin ◽  
H Murakoshi ◽  
K J Rhodes ◽  
J S Trimmer
Keyword(s):  
Amino Acids ◽  
Influenza Virus ◽  
Mdck Cells ◽  
Chimeric Protein ◽  
High Density ◽  
K Channel ◽  
Wild Type ◽  
Lateral Membrane ◽  
Channel Proteins ◽  
Hemagglutinin Protein

The voltage-sensitive K+ channel Kv2.1 has a polarized and clustered distribution in neurons. To investigate the basis for this localization, we expressed wild-type Kv2.1 and two COOH-terminal truncation mutants, delta C318 and delta C187, in polarized epithelial MDCK cells. These functional channel proteins had differing subcellular localization, in that while both wild-type Kv2.1 and delta C187 localized to the lateral membrane in high density clusters, delta C318 was expressed uniformly on both apical and lateral membranes. A chimeric protein containing the hemagglutinin protein from influenza virus and the region of Kv2.1 that differentiates the two truncation mutants (amino acids 536-666) was also expressed in MDCK cells, where it was found in high density clusters similar to those observed for Kv2.1. Polarized expression and clustering of Kv2.1 correlates with detergent solubility, suggesting that interaction with the detergent insoluble cytoskeleton may be necessary for proper localization of this channel.

scholarly journals Molecular Architecture of the Voltage-Dependent Na Channel

2001 ◽  
Vol 118 (2) ◽  
pp. 171-182 ◽  
Author(s):  
Toshio Yamagishi ◽  
Ronald A. Li ◽  
Kate Hsu ◽  
Eduardo Marbán ◽  
Gordon F. Tomaselli
Keyword(s):  
Amino Acids ◽  
Structure Prediction ◽  
K Channel ◽  
Na Channel ◽  
Molecular Architecture ◽  
Ionic Selectivity ◽  
Critical Feature ◽  
K Channels ◽  
Voltage Dependent ◽  
Α Helix

The permeation pathway of the Na channel is formed by asymmetric loops (P segments) contributed by each of the four domains of the protein. In contrast to the analogous region of K channels, previously we (Yamagishi, T., M. Janecki, E. Marban, and G. Tomaselli. 1997. Biophys. J. 73:195–204) have shown that the P segments do not span the selectivity region, that is, they are accessible only from the extracellular surface. The portion of the P-segment NH2-terminal to the selectivity region is referred to as SS1. To explore further the topology and functional role of the SS1 region, 40 amino acids NH2-terminal to the selectivity ring (10 in each of the P segments) of the rat skeletal muscle Na channel were substituted by cysteine and expressed in tsA-201 cells. Selected mutants in each domain could be blocked with high affinity by externally applied Cd2+ and were resistant to tetrodotoxin as compared with the wild-type channel. None of the externally applied sulfhydryl-specific methanethiosulfonate reagents modified the current through any of the mutant channels. Both R395C and R750C altered ionic selectivity, producing significant increases in K+ and NH4+ currents. The pattern of side chain accessibility is consistent with a pore helix like that observed in the crystal structure of the bacterial K channel, KcsA. Structure prediction of the Na channel using the program PHDhtm suggests an α helix in the SS1 region of each domain channel. We conclude that each of the P segments undergoes a hairpin turn in the permeation pathway, such that amino acids on both sides of the putative selectivity filter line the outer mouth of the pore. Evolutionary conservation of the pore helix motif from bacterial K channels to mammalian Na channels identifies this structure as a critical feature in the architecture of ion selective pores.

scholarly journals Distinct lipid bilayer compositions have general and protein-specific effects on K+ channel function

2021 ◽  
Vol 153 (2) ◽  
Author(s):  
Laura-Marie Winterstein ◽  
Kerri Kukovetz ◽  
Ulf-Peter Hansen ◽  
Indra Schroeder ◽  
James L. Van Etten ◽  
...  
Keyword(s):  
Amino Acids ◽  
Plasma Membranes ◽  
K Channel ◽  
General Effect ◽  
K Channels ◽  
Channel Function ◽  
Specific Effects ◽  
Unitary Conductance ◽  
Cationic Amino Acids ◽  
The Impact

It has become increasingly apparent that the lipid composition of cell membranes affects the function of transmembrane proteins such as ion channels. Here, we leverage the structural and functional diversity of small viral K+ channels to systematically examine the impact of bilayer composition on the pore module of single K+ channels. In vitro–synthesized channels were reconstituted into phosphatidylcholine bilayers ± cholesterol or anionic phospholipids (aPLs). Single-channel recordings revealed that a saturating concentration of 30% cholesterol had only minor and protein-specific effects on unitary conductance and gating. This indicates that channels have effective strategies for avoiding structural impacts of hydrophobic mismatches between proteins and the surrounding bilayer. In all seven channels tested, aPLs augmented the unitary conductance, suggesting that this is a general effect of negatively charged phospholipids on channel function. For one channel, we determined an effective half-maximal concentration of 15% phosphatidylserine, a value within the physiological range of aPL concentrations. The different sensitivity of two channel proteins to aPLs could be explained by the presence/absence of cationic amino acids at the interface between the lipid headgroups and the transmembrane domains. aPLs also affected gating in some channels, indicating that conductance and gating are uncoupled phenomena and that the impact of aPLs on gating is protein specific. In two channels, the latter can be explained by the altered orientation of the pore-lining transmembrane helix that prevents flipping of a phenylalanine side chain into the ion permeation pathway for long channel closings. Experiments with asymmetrical bilayers showed that this effect is leaflet specific and most effective in the inner leaflet, in which aPLs are normally present in plasma membranes. The data underscore a general positive effect of aPLs on the conductance of K+ channels and a potential interaction of their negative headgroup with cationic amino acids in their vicinity.

Enhanced role of K+ channels in relaxations of hypercholesterolemic rabbit carotid artery to NO

1995 ◽  
Vol 269 (3) ◽  
pp. H805-H811 ◽  
Author(s):  
S. Najibi ◽  
R. A. Cohen
Keyword(s):  
Carotid Artery ◽  
Sodium Nitroprusside ◽  
Channel Blocker ◽  
Isometric Tension ◽  
K Channel ◽  
K Channels ◽  
Rabbit Carotid Artery ◽  
Cyclic Monophosphate ◽  
Endothelium Dependent Relaxation

Endothelium-dependent relaxations to acetylcholine remain normal in the carotid artery of hypercholesterolemic rabbits, but unlike endothelium-dependent relaxations of normal rabbits, they are inhibited by charybdotoxin, a specific blocker of Ca(2+)-dependent K+ channels. Because nitric oxide (NO) is the mediator of endothelium-dependent relaxation and can activate Ca(2+)-dependent K+ channels directly or via guanosine 3',5'-cyclic monophosphate, the present study investigated the role of Ca(2+)-dependent K+ channels in relaxations caused by NO, sodium nitroprusside, and 8-bromoguanosine 3',5'-cyclic monophosphate (8-Brc-GMP) in hypercholesterolemic rabbit carotid artery. Isometric tension was measured in rabbit carotid artery denuded of endothelium from normal and hypercholesterolemic rabbits which were fed 0.5% cholesterol for 12 wk. Under control conditions, relaxations to all agents were similar in normal and hypercholesterolemic rabbit arteries. Charybdotoxin had no significant effect on relaxations of normal arteries to NO, sodium nitroprusside, or 8-BrcGMP, but the Ca(2+)-dependent K+ channel blocker significantly inhibited the relaxations caused by each of these agents in the arteries from hypercholesterolemic rabbits. By contrast, relaxations to the calcium channel blocker nifedipine were potentiated to a similar extent by charybdotoxin in both groups. In addition, arteries from hypercholesterolemic rabbits relaxed less than normal to sodium nitroprusside when contracted with depolarizing potassium solution. These results indicate that although nitrovasodilator relaxations are normal in the hypercholesterolemic rabbit carotid artery, they are mediated differently, and to a greater extent, by Ca(2+)-dependent K+ channels. These data also suggest that K+ channel-independent mechanism(s) are impaired in hypercholesterolemia.

Interactions of mouse glycophorin A with the dRTA-related mutant G719D of the mouse Cl–/HCO3– exchanger Ae1This paper is one of a selection of papers published in a Special Issue entitled CSBMCB 53rd Annual Meeting — Membrane Proteins in Health and Disease, and has undergone the Journal’s usual peer review process.

2011 ◽  
Vol 89 (2) ◽  
pp. 224-235 ◽  
Author(s):  
Andrew K. Stewart ◽  
Fouad T. Chebib ◽  
Syed W. Akbar ◽  
Maria J. Salas ◽  
Rajan A. Sonik ◽  
...  
Keyword(s):  
Amino Acids ◽  
Transmembrane Domain ◽  
Peer Review Process ◽  
Surface Expression ◽  
Amino Acid Sequences ◽  
Glycophorin A ◽  
Specific Expression ◽  
Health And Disease ◽  
Renal Tubular

The AE1 mutation G701D, associated with recessive distal renal tubular acidosis (dRTA), produces only minimal erythroid phenotype, reflecting erythroid-specific expression of stimulatory AE1 subunit glycophorin A (GPA). GPA transgene expression could theoretically treat recessive dRTA in patients and in mice expressing cognate Ae1 mutation G719D. However, human (h) GPA and mouse (m) Gpa amino acid sequences are widely divergent, and mGpa function in vitro has not been investigated. We therefore studied in Xenopus oocytes the effects of coexpressed mGpa and hGPA on anion transport by erythroid (e) and kidney (k) isoforms of wild-type mAe1 (meAe1, mkAe1) and of mAe1 mutant G719D. Coexpression of hGPA or mGpa enhanced the function of meAe1 and mkAe1 and rescued the nonfunctional meAe1 and mkAe1 G719D mutants through increased surface expression. Progressive N-terminal truncation studies revealed a role for meAe1 amino acids 22–28 in GPA-responsiveness of meAe1 G719D. MouseN-cyto/humanTMD and humanN-cyto/mouseTMD kAE1 chimeras were active and GPA-responsive. In contrast, whereas chimera mkAe1N-cyto/hkAE1 G701DTMD was GPA-responsive, chimera hkAE1N-cyto/mkAe1 G719DTMD was GPA-insensitive. Moreover, whereas the isolated transmembrane domain (TMD) of hAE1 G701D was GPA-responsive, that of mAe1 G719D was GPA-insensitive. Thus, mGpa increases surface expression and activity of meAe1 and mkAe1. However, the G719D mutation renders certain mAe1 mutant constructs GPA-unresponsive and highlights a role for erythroid-specific meAe1 amino acids 22–28 in GPA-responsiveness.

scholarly journals Correlation between Charge Movement and Ionic Current during Slow Inactivation in Shaker K+ Channels

1997 ◽  
Vol 110 (5) ◽  
pp. 579-589 ◽  
Author(s):  
Riccardo Olcese ◽  
Ramón Latorre ◽  
Ligia Toro ◽  
Francisco Bezanilla ◽  
Enrico Stefani
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Ionic Current ◽  
K Channel ◽  
Charge Movement ◽  
Slow Inactivation ◽  
Gating Currents ◽  
Similar Time ◽  
K Channels ◽  
Recovery From Inactivation

Prolonged depolarization induces a slow inactivation process in some K+ channels. We have studied ionic and gating currents during long depolarizations in the mutant Shaker H4-Δ(6–46) K+ channel and in the nonconducting mutant (Shaker H4-Δ(6–46)-W434F). These channels lack the amino terminus that confers the fast (N-type) inactivation (Hoshi, T., W.N. Zagotta, and R.W. Aldrich. 1991. Neuron. 7:547–556). Channels were expressed in oocytes and currents were measured with the cut-open-oocyte and patch-clamp techniques. In both clones, the curves describing the voltage dependence of the charge movement were shifted toward more negative potentials when the holding potential was maintained at depolarized potentials. The evidences that this new voltage dependence of the charge movement in the depolarized condition is associated with the process of slow inactivation are the following: (a) the installation of both the slow inactivation of the ionic current and the inactivation of the charge in response to a sustained 1-min depolarization to 0 mV followed the same time course; and (b) the recovery from inactivation of both ionic and gating currents (induced by repolarizations to −90 mV after a 1-min inactivating pulse at 0 mV) also followed a similar time course. Although prolonged depolarizations induce inactivation of the majority of the channels, a small fraction remains non–slow inactivated. The voltage dependence of this fraction of channels remained unaltered, suggesting that their activation pathway was unmodified by prolonged depolarization. The data could be fitted to a sequential model for Shaker K+ channels (Bezanilla, F., E. Perozo, and E. Stefani. 1994. Biophys. J. 66:1011–1021), with the addition of a series of parallel nonconducting (inactivated) states that become populated during prolonged depolarization. The data suggest that prolonged depolarization modifies the conformation of the voltage sensor and that this change can be associated with the process of slow inactivation.

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