-
BMC Bioinformatics Jan 2004The family of voltage-gated potassium channels comprises a functionally diverse group of membrane proteins. They help maintain and regulate the potassium ion-based... (Review)
Review
BACKGROUND
The family of voltage-gated potassium channels comprises a functionally diverse group of membrane proteins. They help maintain and regulate the potassium ion-based component of the membrane potential and are thus central to many critical physiological processes. VKCDB (Voltage-gated potassium [K] Channel DataBase) is a database of structural and functional data on these channels. It is designed as a resource for research on the molecular basis of voltage-gated potassium channel function.
DESCRIPTION
Voltage-gated potassium channel sequences were identified by using BLASTP to search GENBANK and SWISSPROT. Annotations for all voltage-gated potassium channels were selectively parsed and integrated into VKCDB. Electrophysiological and pharmacological data for the channels were collected from published journal articles. Transmembrane domain predictions by TMHMM and PHD are included for each VKCDB entry. Multiple sequence alignments of conserved domains of channels of the four Kv families and the KCNQ family are also included. Currently VKCDB contains 346 channel entries. It can be browsed and searched using a set of functionally relevant categories. Protein sequences can also be searched using a local BLAST engine.
CONCLUSIONS
VKCDB is a resource for comparative studies of voltage-gated potassium channels. The methods used to construct VKCDB are general; they can be used to create specialized databases for other protein families. VKCDB is accessible at http://vkcdb.biology.ualberta.ca.
Topics: Animals; Databases, Protein; Humans; Potassium Channels, Voltage-Gated
PubMed: 14715090
DOI: 10.1186/1471-2105-5-3 -
The Journal of General Physiology Nov 1999The members of the voltage-dependent potassium channel family subserve a variety of functions and are expected to have voltage sensors with different sensitivities. The...
The members of the voltage-dependent potassium channel family subserve a variety of functions and are expected to have voltage sensors with different sensitivities. The Shaker channel of Drosophila, which underlies a transient potassium current, has a high voltage sensitivity that is conferred by a large gating charge movement, approximately 13 elementary charges. A Shaker subunit's primary voltage-sensing (S4) region has seven positively charged residues. The Shab channel and its homologue Kv2.1 both carry a delayed-rectifier current, and their subunits have only five positively charged residues in S4; they would be expected to have smaller gating-charge movements and voltage sensitivities. We have characterized the gating currents and single-channel behavior of Shab channels and have estimated the charge movement in Shaker, Shab, and their rat homologues Kv1.1 and Kv2.1 by measuring the voltage dependence of open probability at very negative voltages and comparing this with the charge-voltage relationships. We find that Shab has a relatively small gating charge, approximately 7.5 e(o). Surprisingly, the corresponding mammalian delayed rectifier Kv2.1, which has the same complement of charged residues in the S2, S3, and S4 segments, has a gating charge of 12.5 e(o), essentially equal to that of Shaker and Kv1.1. Evidence for very strong coupling between charge movement and channel opening is seen in two channel types, with the probability of voltage-independent channel openings measured to be below 10(-9) in Shaker and below 4 x 10(-8) in Kv2.1.
Topics: Amino Acid Sequence; Animals; Conserved Sequence; Delayed Rectifier Potassium Channels; Drosophila Proteins; Electric Conductivity; Ion Channel Gating; Kinetics; Membrane Potentials; Molecular Sequence Data; Oocytes; Patch-Clamp Techniques; Potassium Channels; Potassium Channels, Voltage-Gated; Rats; Shab Potassium Channels; Shaker Superfamily of Potassium Channels; Xenopus laevis
PubMed: 10539976
DOI: 10.1085/jgp.114.5.723 -
American Journal of Physiology. Heart... Jul 2002In dogs and in humans, potassium channels formed by ether-a-go-go-related gene 1 protein ERG1 (KCNH2) and KCNQ1 alpha-subunits, in association with KCNE beta-subunits,...
In dogs and in humans, potassium channels formed by ether-a-go-go-related gene 1 protein ERG1 (KCNH2) and KCNQ1 alpha-subunits, in association with KCNE beta-subunits, play a role in normal repolarization and may contribute to abnormal repolarization associated with long QT syndrome (LQTS). The molecular basis of repolarization in horse heart is unknown, although horses exhibit common cardiac arrhythmias and may receive drugs that induce LQTS. In horse heart, we have used immunoblotting and immunostaining to demonstrate the expression of ERG1, KCNQ1, KCNE1, and KCNE3 proteins and RT-PCR to detect KCNE2 message. Peptide N-glycosidase F-sensitive forms of horse ERG1 (145 kDa) and KCNQ1 (75 kDa) were detected. Both ERG1 and KCNQ1 coimmunoprecipitated with KCNE1. Cardiac action potential duration was prolonged by antagonists of either ERG1 (MK-499, cisapride) or KCNQ1/KCNE1 (chromanol 293B). Patch-clamp analysis confirmed the presence of a slow delayed rectifier current. These data suggest that repolarizing currents in horses are similar to those of other species, and that horses are therefore at risk for acquired LQTS. The data also provide unique evidence for coassociation between ERG1 and KCNE1 in cardiac tissue.
Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Benzopyrans; Cell Line; Cisapride; Cricetinae; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Horses; Humans; Immunoblotting; Immunohistochemistry; In Vitro Techniques; KCNQ Potassium Channels; KCNQ1 Potassium Channel; Long QT Syndrome; Myocardium; Patch-Clamp Techniques; Piperidines; Potassium; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Binding; RNA, Messenger; Swine
PubMed: 12063283
DOI: 10.1152/ajpheart.00622.2001 -
The Journal of Biological Chemistry Jul 2001To interpret the recent atomic structures of the Kv (voltage-dependent potassium) channel T1 domain in a functional context, we must understand both how the T1 domain is...
To interpret the recent atomic structures of the Kv (voltage-dependent potassium) channel T1 domain in a functional context, we must understand both how the T1 domain is integrated into the full-length functional channel protein and what functional roles the T1 domain governs. The T1 domain clearly plays a role in restricting Kv channel subunit heteromultimerization. However, the importance of T1 tetramerization for the assembly and retention of quarternary structure within full-length channels has remained controversial. Here we describe a set of mutations that disrupt both T1 assembly and the formation of functional channels and show that these mutations produce elevated levels of the subunit monomer that becomes subject to degradation within the cell. In addition, our experiments reveal that the T1 domain lends stability to the full-length channel structure, because channels lacking the T1 containing N terminus are more easily denatured to monomers. The integration of the T1 domain ultrastructure into the full-length channel was probed by proteolytic mapping with immobilized trypsin. Trypsin cleavage yields an N-terminal fragment that is further digested to a tetrameric domain, which remains reactive with antisera to T1, and that is similar in size to the T1 domain used for crystallographic studies. The trypsin-sensitive linkages retaining the T1 domain are cleaved somewhat slowly over hours. Therefore, they seem to be intermediate in trypsin resistance between the rapidly cleaved extracellular linker between the first and second transmembrane domains, and the highly resistant T1 core, and are likely to be partially structured or contain dynamic structure. Our experiments suggest that tetrameric atomic models obtained for the T1 domain do reflect a structure that the T1 domain sequence forms early in channel assembly to drive subunit protein tetramerization and that this structure is retained as an integrated stabilizing structural element within the full-length functional channel.
Topics: Animals; Blotting, Western; COS Cells; Cell Membrane; Dimerization; Kv1.1 Potassium Channel; Microscopy, Confocal; Models, Chemical; Models, Molecular; Mutation; Point Mutation; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Conformation; Protein Structure, Tertiary; Transfection; Trypsin; Two-Hybrid System Techniques
PubMed: 11312262
DOI: 10.1074/jbc.M010540200 -
Pharmacological Reviews Jan 2017A subset of potassium channels is regulated primarily by changes in the cytoplasmic concentration of ions, including calcium, sodium, chloride, and protons. The eight... (Review)
Review
A subset of potassium channels is regulated primarily by changes in the cytoplasmic concentration of ions, including calcium, sodium, chloride, and protons. The eight members of this subfamily were originally all designated as calcium-activated channels. More recent studies have clarified the gating mechanisms for these channels and have documented that not all members are sensitive to calcium. This article describes the molecular relationships between these channels and provides an introduction to their functional properties. It also introduces a new nomenclature that differentiates between calcium- and sodium-activated potassium channels.
Topics: Animals; Calcium; Chlorides; Humans; Intermediate-Conductance Calcium-Activated Potassium Channels; Ion Channel Gating; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; Male; Potassium Channels; Potassium Channels, Calcium-Activated; Sodium; Spermatozoa; Terminology as Topic
PubMed: 28267675
DOI: 10.1124/pr.116.012864 -
FEBS Letters Dec 1996Heteromultimer formation between Kv potassium channel subfamilies with the production of a novel current is reported for the first time. Protein-protein interactions...
Heteromultimer formation between Kv potassium channel subfamilies with the production of a novel current is reported for the first time. Protein-protein interactions between Kv2.1 and electrically silent Kv6.1 alpha-subunits were detected using two microelectrode voltage clamp and yeast two-hybrid measurements. Amino terminal portions of Kv6.1 were unable to form homomultimers but interacted specifically with amino termini of Kv2.1. Xenopus oocytes co-injected with Kv6.1 and Kv2.1 cRNAs exhibited a novel current with decreased rates of deactivation, decreased sensitivity to TEA block, and a hyperpolarizing shift of the half maximal activation potential when compared to Kv2.1. Our results indicate that Kv channel subfamilies can form heteromultimeric channels and, for the first time, suggest a possible functional role for the Kv6 subfamily.
Topics: Animals; Patch-Clamp Techniques; Potassium Channel Blockers; Potassium Channels; Recombinant Fusion Proteins; Shab Potassium Channels; Tetraethylammonium; Tetraethylammonium Compounds; Xenopus
PubMed: 8980147
DOI: 10.1016/s0014-5793(96)01316-6 -
The Journal of Biological Chemistry Mar 2000We present the cloning and characterization of two novel calcium-activated potassium channel beta subunits, hKCNMB3 and hKCNMB4, that are enriched in the testis and...
We present the cloning and characterization of two novel calcium-activated potassium channel beta subunits, hKCNMB3 and hKCNMB4, that are enriched in the testis and brain, respectively. We compare and contrast the steady state and kinetic properties of these beta subunits with the previously cloned mouse beta1 (mKCNMB1) and the human beta2 subunit (hKCNMB2). Once inactivation is removed, we find that hKCNMB2 has properties similar to mKCNMB1. hKCNMB2 slows Hslo1 channel gating and shifts the current-voltage relationship to more negative potentials. hKCNMB3 and hKCNMB4 have distinct effects on slo currents not observed with mKCNMB1 and hKCNMB2. Although we found that hKCNMB3 does interact with Hslo channels, its effects on Hslo1 channel properties were slight, increasing Hslo1 activation rates. In contrast, hKCNMB4 slows Hslo1 gating kinetics, and modulates the apparent calcium sensitivity of Hslo1. We found that the different effects of the beta subunits on some Hslo1 channel properties are calcium-dependent. mKCNMB1 and hKCNMB2 slow activation at 1 microM but not at 10 microM free calcium concentrations. hKCNMB4 decreases Hslo1 channel openings at low calcium concentrations but increases channel openings at high calcium concentrations. These results suggest that beta subunits in diverse tissue types fine-tune slo channel properties to the needs of a particular cell.
Topics: Amino Acid Sequence; Brain; Calcium; Cloning, Molecular; Humans; Ion Channel Gating; Kinetics; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; Large-Conductance Calcium-Activated Potassium Channel beta Subunits; Large-Conductance Calcium-Activated Potassium Channels; Male; Molecular Sequence Data; Nerve Tissue Proteins; Patch-Clamp Techniques; Potassium Channels; Potassium Channels, Calcium-Activated; RNA, Messenger; Sequence Alignment; Testis
PubMed: 10692449
DOI: 10.1074/jbc.275.9.6453 -
Proceedings of the National Academy of... Feb 2022We report two structures of the human voltage-gated potassium channel (Kv) Kv1.3 in immune cells alone (apo-Kv1.3) and bound to an immunomodulatory drug called...
We report two structures of the human voltage-gated potassium channel (Kv) Kv1.3 in immune cells alone (apo-Kv1.3) and bound to an immunomodulatory drug called dalazatide (dalazatide-Kv1.3). Both the apo-Kv1.3 and dalazatide-Kv1.3 structures are in an activated state based on their depolarized voltage sensor and open inner gate. In apo-Kv1.3, the aromatic residue in the signature sequence (Y447) adopts a position that diverges 11 Å from other K channels. The outer pore is significantly rearranged, causing widening of the selectivity filter and perturbation of ion binding within the filter. This conformation is stabilized by a network of intrasubunit hydrogen bonds. In dalazatide-Kv1.3, binding of dalazatide to the channel's outer vestibule narrows the selectivity filter, Y447 occupies a position seen in other K channels, and this conformation is stabilized by a network of intersubunit hydrogen bonds. These remarkable rearrangements in the selectivity filter underlie Kv1.3's transition into the drug-blocked state.
Topics: Amino Acid Sequence; Binding Sites; Humans; Ion Channel Gating; Kv1.3 Potassium Channel; Membrane Potentials; Microscopy, Electron; Models, Molecular; Molecular Conformation; Potassium; Potassium Channels; Potassium Channels, Voltage-Gated; Sequence Alignment
PubMed: 35091471
DOI: 10.1073/pnas.2113536119 -
Journal of the American College of... Jul 2000It is becoming clear that mutations in the KVLQT1, human "ether-a-go-go" related gene, cardiac voltage-dependent sodium channel gene, minK and MiRP1 genes, respectively,... (Review)
Review
It is becoming clear that mutations in the KVLQT1, human "ether-a-go-go" related gene, cardiac voltage-dependent sodium channel gene, minK and MiRP1 genes, respectively, are responsible for the LQT1, LQT2, LQT3, LQT5 and LQT6 variants of the Romano-Ward syndrome, characterized by autosomal dominant transmission and no deafness. The much rarer Jervell-Lange-Nielsen syndrome (with marked QT prolongation and sensorineural deafness) arises when a child inherits mutant KVLQT1 or minK alleles from both parents. In addition, some families are not linked to the known genetic loci. Cardiac voltage-dependent sodium channel gene encodes the cardiac sodium channel, and long QT syndrome (LQTS) mutations prolong action potentials by increasing inward plateau sodium current. The other mutations cause a decrease in net repolarizing current by reducing potassium currents through "dominant negative" or "loss of function" mechanisms. Polymorphic ventricular tachycardia (torsade de pointes) is thought to be initiated by early after-depolarizations in the Purkinje system and maintained by reentry in the myocardium. Clinical presentations vary with the specific gene affected and the specific mutation. Nevertheless, patients with identical mutations can also present differently, and some patients with LQTS mutations may have no manifest baseline phenotype. The question of whether the latter situation is one of high risk for administration of QT prolonging drugs or during myocardial ischemia is under active investigation. More generally, the identification of LQTS genes has provided tremendous new insights for our understanding of normal cardiac electrophysiology and its perturbation in a wide range of conditions associated with sudden death. It seems likely that the approach of applying information from the genetics of uncommon congenital syndromes to the study of common acquired diseases will be an increasingly important one in the next millennium.
Topics: Cardiac Pacing, Artificial; Cation Transport Proteins; DNA-Binding Proteins; ERG1 Potassium Channel; Electric Countershock; Electrocardiography; Ether-A-Go-Go Potassium Channels; Humans; KCNQ Potassium Channels; KCNQ1 Potassium Channel; Long QT Syndrome; Mutation; NAV1.5 Voltage-Gated Sodium Channel; Potassium Channels; Potassium Channels, Voltage-Gated; Purkinje Fibers; Sodium Channels; Trans-Activators; Transcriptional Regulator ERG
PubMed: 10898405
DOI: 10.1016/s0735-1097(00)00716-6 -
The Journal of Physiology Jul 2003The effect of glycosylation on Kv1.l potassium channel function was investigated in mammalian cells stably transfected with Kv1.l or Kv1.1N207Q. Macroscopic current...
The effect of glycosylation on Kv1.l potassium channel function was investigated in mammalian cells stably transfected with Kv1.l or Kv1.1N207Q. Macroscopic current analysis showed that both channels were expressed but Kv1.1N207Q, which was not glycosylated, displayed functional differences compared with wild-type, including slowed activation kinetics, a positively shifted V 1/2, a shallower slope for the conductance versus voltage relationship, slowed C-type inactivation kinetics, and a reduced extent of and recovery from C-type inactivation. Kv1. 1N207Q activation properties were also less sensitive to divalent cations compared with those of Kv1.l. These effects were largely due to the lack of trans-Golgi added sugars, such as galactose and sialic acid, to the N207 carbohydrate tree. No apparent change in ionic current deactivation kinetics was detected inKv1.1N207Q compared with wild-type. Our data, coupled with modelling, suggested that removal of the N207 carbohydrate tree had two major effects. The first effect slowed the concerted channel transition from the last dosed state to the open state without changing the voltage dependence of its kinetics. This effect contributed to the G-V curve depolarization shift and together with the lower sensitivity to divalent cations suggested that the carbohydrate tree and its negatively charged sialic acids affected the negative surface charge density on the channel's extracellular face that was sensed by the activation gating machinery. The second effect reduced a cooperativity factor that slowed the transition from the open state to the dosed state without changing its voltage dependence. This effect accounted for the shallower G-V slope, and contributed to the depolarized G-V shift, and together with the inactivation changes it suggested that the carbohydrate tree also affected channel conformations. Thus N-glycosylation, and particularly terminal sialylation, affected Kv1.l gating properties both by altering the surface potential sensed by the channel's activation gating machinery and by modifying conformational changes regulating cooperative subunit interactions during activation and inactivation. Differences in glycosylation pattern among closely related channels may contribute to their functional differences and affect their physiological roles.
Topics: Amino Acid Sequence; Animals; CHO Cells; Cations, Divalent; Cricetinae; Electric Conductivity; Extracellular Fluid; Glycoproteins; Glycosylation; Homeostasis; Ion Channel Gating; Ion Channels; Kinetics; Kv1.1 Potassium Channel; Molecular Sequence Data; Potassium Channels; Potassium Channels, Voltage-Gated; Rats
PubMed: 12879861
DOI: 10.1113/jphysiol.2003.040337