TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameOrganismal TypeExample

2 TMS K+ channel (conducts K+ (KD = 8 mM); blocked by Na+ (190 mM) (Renart et al., 2006) and tetrabutylammonium (Iwamoto et al., 2006)). Ion permeation occurs by ion-ion contacts in single file fashion through the selectivity filter (Köpfer et al. 2014).  The C-terminal domain mediates pH modulation (Hirano et al., 2011Pau et al., 2007). KcsA exhibits a global twisting motion upon gating (Shimizu et al., 2008).  Activity is influenced by the phase of the lipid bilayer (Seeger et al. 2010), and occupancy of nonannular lipid binding sites increases the stability of the tetrameric complex (Triano et al. 2010).  The open conformation of KcsA can disturb the bilayer integrity and catalyze the flipping of phospholipids (Nakao et al. 2014).  This protein is identical to the KcsA orthologue (P0A333) in Streptomyces coelicolor.

Gram-positive bacteria

Skc1 (KcsA) of Streptomyces lividans

Sorbitol transporter of 535 aas


SOT1 of Pyrus pyrifolia (Chinese pear) (Pyrus serotina)

Voltage-sensitive K+ channel (PNa+/PK+ ≈ 0.1) Shaker and Shab K+ channels are blocked by quinidine (Gomez-Lagunas, 2010).


Shab11 of Drosophila melanogaster

Voltage-sensitive K+ channel


Shaw2 of Drosophila melanogaster

Voltage-sensitive fast transient outward current neurons and muscle in flies and worms (Fawcett et al., 2006)
Shal2 of Drosophila melanogaster

Margatoxin-sensitive voltage-gated K+ channel, Kv1.3 (in plasma and mitochondrial membranes of T lymphocytes) (Szabò et al., 2005). Kv1.3 associates with the sequence similar (>80%) Kv1.5 protein in macrophage forming heteromers that like Kv1.3 homomers are r-margatoxin sensitive (Vicente et al., 2006). However, the heteromers have different biophysical and pharmacological properties. The Kv1.3 mitochondrial potassium channel is involved in apoptotic signalling in lymphocytes (Gulbins et al., 2010). Interactions between the C-terminus  of Kv1.5 and Kvβ regulate pyridine nucleotide-dependent changes in channel gating (Tipparaju et al., 2012).  INtracellular trafficking of the KV1.3 K+ channel is regulated by the pro-domain of a matrix metalloprotease (Nguyen et al. 2013).


Kv1.3 homomers and Kv1.3/Kv1.5 heteromers of Homo sapiens (P22001)
Kv1.3 (P22001)
Kv1.5 (P19024)

Voltage-gated K+ channel subfamily D, member 2, Kv4.2 or KCND2, in neurons and muscle; forms complexes with auxiliary subunits and scaffolding proteins via its N-terminus, influencing trafficking, temperature-sensitivity and gating (Radicke et al. 2013).These subunits are (1) dipeptidyl-peptidase-like type II transmembrane proteins typified by DPPX-S (e.g., protein 6, P42658; 865 aas), and (2) cytoplasmic Ca2+ binding proteins known as K+ channel interacting proteins (KChIPs; TC#5.B.1.1.7; Q6PIL6) (Seikel and Trimmer 2009).  The C-terminus interacts with KChIP2 to influence gating, surface trafficking and gene expression (Han et al., 2006; Schwenk et al., 2008). KChIPs (250 aas for mouse KChIP4a; Q6PHZ8) are homologous to domains in NADPH oxidases (5.B.1). Heteropoda toxin 2 (P58426; PDB 1EMX) interactions with Kv4.3 and Kv4.1 give rise to differences in gating modifications (DeSimone et al., 2011).  Mutations cause autism and seizures due to a slowing of channel inactivation (Lee et al. 2014).


Kv4.2 of Homo sapiens (Q9NZV8)

Voltage-gated K channel, Shaker. Shaker and Shab K channels are blocked by quinidine (Gomez-Lagunas, 2010). Also regulated by unsaturated fatty acids (Börjesson and Elinder, 2011).  TMSs 3 and 4 comprise the voltage sensor paddle (Xu et al. 2013).


Shaker of Drosophila melanogaster (CAA29917)

Electrically silent lens epithelium K+ channel (Delayed rectifier K+ channel α-subunit, Kv9.1 (Shepard & Rae, 1999))


Kv9.1 of Homo sapiens

Voltage gated K+ channel/MiNK related peptide (MiRP) complex, KVS1(α)/MPS-1/MiRPβ (expressed in chemo- and mechano-sensory neurons. Involved in chemotaxis, mechanotransduction and locomotion (Bianchi et al., 2003)). KVS-1 and KVS-2 are homologous; MPS-1 is member of the MiNK family (8.A.10). KVS-1/MPS-1 association involves hydrophobic forces (Wang and Sesti, 2007).


KVS-1 (α)/ MPS-1 (MiRPβ) of Caenorhabditis elegans
KVS-1 (α) (Q86GI9)
MPS-1 (MiRPβ) (Q86GJ0)

Brain-specific regulatory α-chain homologue that coassembles with other α-subunits to form active heteromultimeric K+ channels of unique kinetic properties, Kv2.3r. The functional expression of this regulatory α-subunit represents a novel mechanism without precedents in voltage-gated channels, which contributes to the functional diversity of K+ channels (Castellano et al., 1997).
Kv2.3r of Rattus norvegicus (P97557)

Voltage-gated K+ channel, chain A, Shaker-related, Kv1.2 (Crystal structure known, Long et al., 2007; Chen et al. 2010). Functions with the auxiliary subunit, Ivβ1.2; 8.A.5.1.1) (Peters et al. 2009).  Delemotte et al. (2010) described the effects of sensor domain mutations on molecular dynamics of Kv1.2.  The Sigma 1 receptor (Q99720; Sigma non-opioid intracellular receptor 1) interacts with Kv1.2 to shape neuronal and behavioral responses to cocaine (Kourrich et al. 2013).  Amino acid substitutions cause Shaker to become heat-sensing (opens with increasing temperature as for TrpV1) or cold-sensing (opens with decreasing temperature as for TrpM8) (Chowdhury et al. 2014).


Kv1.2 of Homo sapiens (P16389)

Voltage-gated K+ channel, Shab-related, Kv2.1 (858aas) (Crystal structure known, Long et al., 2007). Rat Kv2.1 and Kv2.2 (long) are colocalized in the somata and proximal dendrites of cortical pyramidal neurons and are capable of forming functional heteromeric delayed rectifier channels. The delayed rectifer currents, which regulate action potential firing, are encoded by heteromeric Kv2 channels in cortical neurons (Kihira et al., 2010). Phosphorylation by AMP-activated protein kinase regulates membrane excitability (Ikematsu et al., 2011). Functional interactions between residues in the S1, S4, and S5 domains of Kv2.1 have been identified (Bocksteins et al., 2011).


Kv2.1/Kv2.2 of Homo sapiens

Voltage-gated K+ channel, Kv1.1 or KCNA1. Regulated by syntaxin through dual action on channel surface expression and conductance (Feinshreiber et al., 2009).  Defects cause episodic ataxia type 1 (EA1), an autosomal dominant K+ channelopathy accompanied by short attacks of cerebellar ataxia and dysarthria (PMID 25642194).


Kv1.1 of Homo sapiens (Q09470)

Voltage-gated K+ channel subfamily C member 3, Kv3.3. Negatively modulated by protein kinase C (Desai et al., 2008). Phosphorylation of Kv3.3 by PKC may allow neurons to maintain action potential height during stimulation at high frequencies, and therefore contributes to stimulus-induced changes in the intrinsic excitability of neurons such as those of the auditory brainstem (Desai et al., 2008).


Kv3.3 of Homo sapiens (Q14003)

Voltage-gated delayed rectifier K+ channel, Kv1 of the octopus. RNA editing underlies adaption (Garrett and Rosenthal, 2012).  94% identical to the squid giant axon delayed rectifier voltage-dependent potassium channel, SqKv1A (Q25376).


Kv1 of Octopus vulgaris (H2EZS9)

Potassium voltage-gated channel subfamily S member 3 (Delayed-rectifier K(+) channel alpha subunit 3) (Voltage-gated potassium channel subunit Kv9.3)
KCNS3 of Homo sapiens

Potassium voltage-gated channel subfamily S member 2 (Delayed-rectifier K(+) channel alpha subunit 2) (Voltage-gated potassium channel subunit Kv9.2)
KCNS2 of Homo sapiens

Potassium voltage-gated channel subfamily G member 3 (Voltage-gated potassium channel subunit Kv10.1) (Voltage-gated potassium channel subunit Kv6.3)
Kcng3 of Rattus norvegicus

Potassium voltage-gated channel subfamily F member 1 (Voltage-gated potassium channel subunit Kv5.1) (kH1)
KCNF1 of Homo sapiens

The voltage-gated K+ channel subfamily D member 3, KCND3 or Kv4.3.  Mutations cause spinocerebellar ataxia type 19 (Duarri et al. 2012).  The crystal structure with its regulatory subunit, Kchip1, has been solved (2NZ0).


KCND3 of Homo sapiens

Ca2+-activated K+ channel. Four pairs of RCK1 and RICK2 domains form the Ca2+-sensing apparatus known as the "gating ring" in BK channel proteins (Savalli et al., 2012).


Ca2+-activated K+ channel of Drosophila melanogaster

Large conductance Ca2  - and voltage-activated K channel, α-subunit (subunit α1), BK, BKCa, Kca1.1, Slo1  or MaxiK (functions with four β-subunits encoded by genes KCNMB1-4 in humans (Toro et al. 2013); the positions of beta2 and beta3 have been determined (Wu et al. 2013).  The KB channel is inhibited by 3 scorpion toxins, charybda toxin, iberiotoxin and slotoxin.  It forms a ''''Ca2  nanodomain'''' complex with Cav1.2 (L-type; 1.A.1.11.4), Cav2.1 (P/Q-type; 1.A.1.11.5), Cav2.2 (N-type; 1.A.1.11.6) where Ca2   influx through the Cav channel activates BKCa (Berkefeld et al., 2006; Romanenko et al., 2006). The RCK2 domain is a Ca2   sensor (Yusifov et al., 2008). Binding of Ca2   to D367 and E535 changes the conformation around the binding site and turns the side chain of M513 into a hydrophobic core, explaining how Ca2   binding opens the activation gate of the channel (Zhang et al., 2010). A structural motif in the C-terminal tail of Slo1 confers carbon monoxide sensitivity to human BKCa channels (Williams et al., 2008; Hou et al., 2008). These channels are present in the inner mitochondrial membrane of rat brain (Douglas et al., 2006).The Stress-Axis Regulated Exon (STREX) is responsible for stretch sensitivity. Ca2   binds to two sites. Ca2   binding to the RCK1 site is voltage dependent, but Ca2   binding to the Ca2   bowl is not (Sweet and Cox et al., 2008). Type 1 IP3 receptors activate BKCa channels via local molecular coupling in arterial smooth muscle cells (Zhao et al., 2010). The open structure is known (Yuan et al., 2012). BKCa is essential for ER calcium uptake in neurons and cardiomyocytes (Kuum et al., 2012) and link Ca2   signaling to action potential firing and neurotransmitter release serotonin receptor in many types of neurons (Rothberg 2012). The molecular mechanism of pharmacological activation of BK channels has been discussed by Gessner et al. (2012). The first TMS of the β2-subunit binds to TMS S1 of the α-subunit (Morera et al., 2012).  Mutations in Cav1.2 give rise to Timothy syndrome (Dixon et al. 2012).  Exhibits low voltage activation by interaction with Cav3 (Rehak et al. 2013) as well as Ca2+-gating (Berkefeld and Fakler 2013). Single-channel kinetics have been reported (Geng and Magleby 2014).


BKCa or MaxiK channel of Rattus norvegicus (Q62976)

Ca2+-activated K+ channel Slo-1 (Maxi K; BK channel) (ethanol-activated; responsible for intoxication) (Davies et al., 2003); tyrosyl phosphorylation regulates BK channels via cortactin (Tian et al. 2008a), but palmitoylation gates phosphorylation-dependent regulation of BK potassium channels (Tian et al., 2008b). Also regulated by Mg2+ which mediates interaction between the voltage sensor and cytosolic domain to activate BK channels (Yang et al., 2007). Modulated by the ss2 subunit (Lee et al., 2010). The structure of the gating ring from the human large-conductance Ca2+-gated K+ channel has been reported (Wu et al., 2010). Four pairs of RCK1 and RICK2 domains form the Ca2+-sensing apparatus known as the "gating ring" in BK channel proteins (Savalli et al., 2012).  The dystrophin complex controls BK channel localization and muscle activity (Kim et al. 2009).


BK K+ channel of Caenorhabditis elegans (Q95V25)

The intracellularly Na+ and Cl--activated delayed rectifier K+ channel, rSlo2 (Slack) (provides protection against ischemia (Yuan et al., 2003). The N-terminal domain of Slack determines the formation and trafficking of Slick/Slack heteromeric sodium-activated potassium channels (Chen et al., 2009).


rSlo2 of Rattus norvegicus (Q9Z258)

Sperm Slo3 high conductance K+ channel, activated by voltage and intracellular alkalinization. In sperm, it gives rise to pH-dependent outwardly rectifying K+ currents. (required for the ensuing acrosome reaction; activated by phosphatidylinositol 4,5-bisphosphate (PIP(2)) (Tang et al., 2010).


Slo3 of Mus musculus (O54982)

Human outward rectifying potassium channel, Slo2.1 of 1135 aas. Produces rapidly activating outward rectifier K+ currents. Activated by high intracellular sodium and chloride levels. Channel activity is inhibited by ATP and by inhalation anesthetics, such as isofluraneInhibited upon stimulation of G-protein coupled receptors such as CHRM1 and GRIA1.  Orthologous to 1.A.1.3.4 (Garg et al. 2013).


Slo2.1 of Homo sapiens

K+ channel, AKT1; may form heteromeric channels with KC1 (TC # 1.A.1.4.9) (Geiger et al., 2009).  Required for seed development and postgermination growth in low potassium (Pyo et al. 2010).


AKT1 of Arabidopsis thaliana

K+channel, KDC1 (voltage and pH-dependent; inward rectifying). Does not form homomeric channels. The C-terminus functions in the formation of heteromeric complexes with other potassium alpha-subunits such as KAT1 (1.A.1.4.7) (Naso et al., 2009).


KDC1 of Daucus carota

Inward rectifying, pH-independent K+ channel, KZM1 (Philippar et al., 2003)
KZM1 of Zea mays (CAD18901)

Guard cell outward rectifying K+ out channel, GORK, controls leaf stomatal pore opening (by increasing solute content) and closing (by decreasing solute content), which in turn controls gas and water loss (Schroeder, 2003).

GORK of Arabidopsis thaliana (CAC17380)

Root stelar K+ outward rectifying channel, SKOR (involved in K+ release into the xylem sap; part of the plant water stress response) (Gaymard et al., 1998).
SKOR of Arabidopsis thaliana (AAF26975)

Heterotetrameric K+ channel, KAT2/AKT2 (Nieves-Cordones et al. 2014). Forms heteromeric channels (2:2 stoichiometry) with KAT1 (1.A.1.4.7) (Lebaudy et al., 2010) (Properties differ from those of homomeric channels; Xicluna et al., 2007).  KAT2 also forms homomeric channels in the plasma membrane (Nieves-Cordones et al. 2014).


AKT2/KAT2 of Arabidopsis thaliana
AKT2 (Q38898)
KAT2 (Q38849)

The voltage-sensitive inward rectifying K+ channel, KAT1 (similar to 1.A.1.4.3; activated by protein 14-3-3 (AAF87262)) (Sottocornola et al., 2006). May also transport Na+ and Cs+ (Nakamura and Gaber, 2009). Forms heterotetrameric channels with KAT2 with a stoichiometry of 2:2 (Lebaudy et al., 2010). The pH-sensor is built of a sensory cloud rather than of single key amino acids (Gonzalez et al., 2011).


KAT1 of Arabidopsis thaliana (Q39128)

Inward rectifying Shaker K+ channel SPIK (AKT6) (expressed in pollen, and involved in pollen tube development) (Mouline et al., 2002).
SPIK of Arabidopsis thaliana

The KC1 (KAT3) potassium channel-like subunit; regulates other channels such as AKT1 (1.A.1.4.1) and KAT1 (1.A.1.4.7) (Duby et al., 2008); may form heteromeric channels with AKT1 (Geiger et al., 2009). It forms a tripartite SNARE-K+ channel complex which regulates KAT3 channel opening (Honsbein et al., 2009).  Tripartite interactions with SNARE (SYP121; SYR1; PEN1) and AKT1 control gating (Grefen et al. 2010).  ZKC1 also forms homoleric channels in the endoplasmic reticulum (Nieves-Cordones et al. 2014).


KC1 of Arabidopsis thaliana (P92960)

Inward rectifier K+ channel AKT1 (45% identical to 1.A.1.4.1; 944aas) (Garciadeblas et al., 2007).


Akt1 of Physcomitrella patens (A5PH36)

Cyclic nucleotide-gated (CNG) nonselective cation channel (PNa+ /PK+ ≈ 1.0)
CNG channel of Ictalurus punctatus

Hyperpolarization-activated and cyclic nucleotide-gated K+ channel, HCN (bCNG-1) (PNa+/PK+ ≈ 0.3). The human orthologue (O88703) is 863 aas in length and catalyzes mixed monovalent cation currents K+:Na+= 4:1 (Lyashchenko and Tibbs et al., 2008). Biel et al. (2009) present a detailed review of hyperpolarization-activated cation-channels. Inhibited by nicotine and epibatidine which bind to the inner pore (Griguoli et al., 2010).


HCN of Mus musculus

Heterotetrameric (3A:1B) rod photoreceptor cyclic GMP-gated cation channel, CNGA1 (Zhong et al., 2002). Defects produce channelopathies (Biel & Michalakis, 2007). A ring of four Glutamate residues (Glu363) in the outer vestibule, and a ring of four Threonines (Thr360) in the inner vestibule of the pore of CNGA1 channels constitute binding sites for permeating ions (Marchesi et al., 2012).  The tetraspanning peripherin-2 (TC# 8.A.40.1.2) links rhodopsin to this cyclic nucleotide-dependent channel in the outer segments of rod photoreceptors.  The G266D retinitis pigmentosa mutation in TMS4 of rhodopsin abolishes binding of peripherin-2 and prevents association with the CNGA1/CNGB1a subunits present in the complex (Becirovic et al. 2014).  External protons cause inactivation (Marchesi et al. 2015).


CNG of Homo sapiens
Subunit A1 (CNGA1)
Subunit B1 (CNGB1)

Olfactory heteromeric cyclic nucleotide-gated cation (mainly Na+, Ca2+) channel CNGA2/CNGA4/CNGB1b (present in sensory cilia of olfactory receptor neurons; activated by odorant-induced increases in cAMP concentration) (Michalakis et al., 2006).
CNGA2 complex of Mus musculus
CNGA2 (Q62398)
CNGA4 (AAI07349)
CNGB1b (NP_001288)

The cyclic nucleotide- and voltage-gated ion (K+, Rb+, Cs+) channel, CNGC1 (inward rectifying) (functions in heavy metal and cation transport, as does CNGC10) (Dreyer and Uozumi, 2011; Zelman et al., 2012).


CNGC1 of Arabidopsis thaliana (O65717)

The cyclic nucleotide-gated ion (K+, Rb+, Cs+) channel, CNGC2 (functions in plant defense responses, as does CNGC4) (Zelman et al., 2012).


CNGC2 of Arabidopsis thaliana (O65718)

The cyclic nucleotide-gated ion (K+, Rb+, Cs+) channel, HLM1 (CNGC4) (mediates the hypersensitive response (HR) of plants in programmed cell death.) Mutants show abnormal cell death and resistance to infection by Pseudomonas syringae (Balagué et al., 2003; Zelman et al., 2012).


HLM1 of Arabidopsis thaliana

The non-selective cation transporter involved in germination, CNGC3 (Gobert et al., 2006; Zelman et al., 2012).


CNG3 of Arabidopsis thaliana (Q9SKD7)

The cyclic nucleotide-gated K+ channel, Sp-tetraKCNG (2238 aas) (Galindo et al., 2007)
Sp-tetraKCNG of Strongylocentrotus purpuratus (ABN14774)

Ortholog K+/Na+ pacemaker channel, Hcn4 (Scicchitano et al., 2012).  Hyperpolarization-activated cyclic nucleotide-regulated HCN channels underlie the Na+-K+ permeable IH pacemaker current. As with other voltage-gated members of the 6-transmembrane KV channel superfamily, opening of HCN channels involves dilation of a helical bundle formed by the intracellular ends of S6, but this is promoted by inward, not outward, displacement of S4. Direct agonist binding to a ring of cyclic nucleotide-binding sites, one of which lies immediately distal to each S6 helix, imparts cAMP sensitivity to HCN channel opening. At depolarized potentials, HCN channels are further modulated by intracellular Mg2+ which blocks the open channel pore and blunts the inhibitory effect of outward K+ flux. Lyashchenko et al. 2014 showed that cAMP binding to the gating ring enhances not only channel opening but also the kinetics of Mg2+ block.


Hcn4 of Homo sapiens (Q9Y3Q4)

Hyperpolarization-activated cyclic nucleotide-gated (HCN) inward current carrying cationic channel, I(f), (HCN2/HCN4) (Ye and Nerbonne, 2009).


HCN2/HCN4 channels of Homo sapiens 
HCN2 (Q9UL51)
HCN4 (Q9Y3Q4) 

Cyclic nucleotide-gated cation channel α3 (CNGA3 or CNG3); photoreceptor cGMP-gated channel α-subunit. Also possibly expressed in inner ear cell cells where it binds to an intracellular C-terminal domain of EMILIN1 (Selvakumar et al., 2012).  Elastic network model analysis of the CNGA3 channel supports a modular model of allosteric gating, according to which protein domains are quasi-independent: they can move independently but are coupled to each other allosterically (Gofman et al. 2014).


CNGA3 of Homo sapiens (Q16281) 

Trout cyclic nucleotide-gated cation channel α3 (CNGA3 or CNG3). Expressed in inner ear cell cells where it binds to an intracellular C-terminus domain of EMILIN1 (Selvakumar et al., 2012). 


CNGA3 of Oncorhynchus mykiss (G9BHJ0)

Probable cyclic nucleotide-gated ion channel 6 (AtCNGC6) (Cyclic nucleotide- and calmodulin-regulated ion channel 6)
CNGC6 of Arabidopsis thaliana

Cyclic nucleotide gated K+ channel of 650 aas


Channel of Naegleria gruberi

Cyanobacterial cyclic nuceotide K+ channel of 454 aas (Brams et al. 2014).


Channel of Trichodesmium erythraeum

Cyclic nucleotide-gated K+channel of 430 aas.  Activated by cAMP, not by cGMP.  Highly specific for K+ over Na+.  Has a C-terminal cAMP-binding domain linked to the 6 TMS channel domain (Brams et al. 2014).


Channel of Spirochaeta thermophila

Cyclic nucleotide-gated cation (CNG) channel of 665 aas.

Animals (Insects)

CNG of Drosophila melanogaster

TAX-2 cyclic nucleotide-gated cation channel-B (CNGB) of 800 aas (Wojtyniak et al. 2013).


TAX-2 CNGB of Caenorhabditis elegans

TAX-4 cyclic nucleotide-gated cation channel A (CNGA) of 733 aas (Wojtyniak et al. 2013).


TAX-4 CNGA of Caenorhabditis elegans

K+ channel protein, PAK2.1 of 543 aas.  Contains a cyclic nucleotide-binding domain (Ling et al. 1998; Jegla and Salkoff 1995).

Alveolata (ciliates)

PAK2.1 of Paramecium tetraurelia

K+ channel protein, PAK11-MAC of 772 aas.  Contains a cyclic nucleotide-binding domain (Ling et al. 1998; Jegla and Salkoff 1995).

Alveolata (ciliates)

PAK11-MAC of Paramecium tetraurleia

K+ channel, MthK
MthK channel protein of Methanococcus jannaschii

Tok1 outward rectifying K+ channel (transports K+ and Cs+) (Bertl et al., 2003)
Tok1 outward rectifier K+ channel of Saccharomyces cerevisiae

AtTPK4 two-pore K+ channel 4 (Becker et al., 2004). Asp86 and Asp200 are essential for K+ permeation as well as inward rectification (Marcel et al., 2010).  Reviewed by González et al. 2014.


AtTPK4 of Arabidopsis thaliana (AAP82009)

The 2-pore (4TMS) outward rectifying K+ channel, KCO1 or 2PK1. Possesses two tandem Ca2+-binding EF-hand motifs, and cytosolic free Ca2+ (~300nM) activates (Czempinski et al., 1997).  Reviewed by González et al. 2014.


KCO1 of Arabidopsis thaliana

The two pore tonoplast TPK-type K+ channel; maintains K+ homeostasis in plant cells (Hamamoto et al., 2008); activated by 14-3-3 proteins (Latz et al., 2007).
TPK1 of Nicotiniana tobacum (A9QMN9)

Two-pore potassium channel 5 (AtTPK5) (Calcium-activated outward-rectifying potassium channel 5, chloroplastic) (AtKCO5).  Reviewed by González et al. 2014.


TPK5 of Arabidopsis thaliana

Potassium inward rectifier (Kir)-like channel 3 (AtKCO3)
KCO3 of Arabidopsis thaliana

Chloroplast thylakoid two-pore calcium and proton-activated K+ channel, TPK3 of 436 aas and 4 TMSs.  Mediates ion counterbalancing, influencing photosynthetic llight utilization (Carraretto et al. 2013).  Reviewed by González et al. 2014.


TPK3 of Arabidopsis thaliana

TWIK-1 inward rectifier K+ channel (Enyedi and Czirják, 2010).  Lipid tails from both the upper and lower leaflets can partially penetrate into the pore (Aryal et al. 2015). The lipid tails do not sterically occlude the pore, but there is an inverse correlation between the presence of water within the hydrophobic barrier and the number of lipids tails within the lining of the pore (Aryal et al. 2015).


TWIK-1 of Mus musculus

TASK-2 (KCNK5) two-pore domain, pH-sensitive, voltage-insensitive, outward rectifying K+ channel (K+ > Rb+ >> Cs+ > NH4+ > Na+ ≈ Li+).  Regulated [inhibited] via group 1 metabotropic glutamate receptors by inositol phosphates (Chemin et al., 2003).  TASK-2 gating is controlled by changes in both extra- and intracellular pH through separate sensors: arginine 224 and lysine 245, located at the extra- and intracellular ends of transmembrane domain 4, respectively. TASK-2 is inhibited by a direct effect of CO2 and is regulated by and interacts with G protein subunits. TASK-2 takes part in regulatory adjustments and is a mediator in the chemoreception process in neurons of the retrotrapezoid nucleus where its pHi sensitivity could be important in regulating excitability and therefore signalling of the O2/CO2 status. Extracellular pH increases brought about by HCO3- efflux from proximal tubule epithelial cells may couple to TASK-2 activation to maintain electrochemical gradients favourable to HCO3- reabsorption. TASK-2 is expressed at the basolateral membrane of proximal tubule cells (López-Cayuqueo et al. 2014).


TASK-2 of Homo sapiens

The 2P-domain K+ channel, TWIK 2 (functions in cell electrogenesis (Patel et al., 2000).
TWIK2 of Homo sapiens

TREK-1 K+ channel subunit (Regulated by group 1 metabotropic glutamate receptors and by diacylglycerols and phosphatidic acids) (Chemin et al., 2003). TREK-1, TREK-2 and TRAAK are all regulated by lysophosphatidic acid, converting these mechano-gated, pH voltage-sensitive channels into leak conductances (Chemin et al., 2005). The mammalian K2P2.1 potassium channel (TREK-1, KCNK2) is highly expressed in excitable tissues, where it plays a key role in the cellular mechanisms of neuroprotection, anaesthesia, pain perception and depression (Cohen et at., 2008). Alternative translation initiation in rat brain yields K2P2.1 potassium channels permeable to sodium (Thomas et al. 2008). The crystal of the human 2-pore domain K+ channel, K2P1 has been solved (Miller and Long, 2012). Multiple modalities converge on a common gate to control K2P channel function (Bagriantsev et al., 2011).  TREK-1 mediates fast and slow glutamate release in astrocytes upon GPCR activation (Woo et al. 2012).


TREK-1 of Mus musculus (P97438)  

KcnK3 K+ channel (TASK1, OAT1, TBAK1) (the K+ leak conductance). TASK1 and 3 may play a role in nontumorigenic primary hyperaldosteronism (Davies et al., 2008).
KcnK3 of Homo sapiens (AAG29340)

Neuronal 2-P (4 TMS) domain K+ membrane tension-gated channel, TRAAK (stimulated by arachidonic acid and polyunsaturated fatty acids (Fink et al., 1998). The crystal structures of conductive and nonconductive human K2P TRAAK K+ channel has been solved (Brohawn et al., 2012; Brohawn et al. 2014). Regulated by mechanical deformation of the membrane and temperature as well as polyunsaturated fatty acids (Brohawn et al., 2012). Multiple modalities converge on a common gate to control K2P channel function (Bagriantsev et al., 2011).  In the non-conductive state, a lipid acyl chain accesses the channel cavity through a 5 Å-wide lateral opening in the membrane inner leaflet and physically blocks ion passage. In the conductive state, rotation of transmembrane helix 4 about a central hinge seals the intramembrane opening, preventing lipid block of the cavity and permitting ion entry. Additional rotation of a membrane interacting TM2-TM3 segment, unique to mechanosensitive K2Ps, against TM4 may further stabilize the conductive conformation. Comparison of the structures provodes a biophysical explanation for TRAAK mechanosensitivity--an expansion in cross-sectional area up to 2.7 nm2 in the conductive state is expected to create a membrane-tension-dependent energy difference between conformations that promotes force activation (Brohawn et al. 2014).  TM helix straightening and buckling may underlie channel activation (Brohawn et al. 2014). Regulated by mechanical deformation of the membrane and temperature as well as polyunsaturated fatty acids (Brohawn et al., 2012). Multiple modalities converge on a common gate to control K2P channel function (Bagriantsev et al., 2011).  In the non-conductive state, a lipid acyl chain accesses the channel cavity through a 5 Å-wide lateral opening in the membrane inner leaflet and physically blocks ion passage. In the conductive state, rotation of transmembrane helix 4 about a central hinge seals the intramembrane opening, preventing lipid block of the cavity and permitting ion entry. Additional rotation of a membrane interacting TM2-TM3 segment, unique to mechanosensitive K2Ps, against TM4 may further stabilize the conductive conformation. Comparison of the structures provodes a biophysical explanation for TRAAK mechanosensitivity--an expansion in cross-sectional area up to 2.7 nm2 in the conductive state is expected to create a membrane-tension-dependent energy difference between conformations that promotes force activation (Brohawn et al. 2014).  TM helix straightening and buckling may underlie channel activation (Brohawn et al. 2014).  TM helix straightening and buckling may underlie channel activation (Lolicato et al. 2014).


TRAAK of Mus musculus (O88454)

Outward rectifying mechanosensitive 2-P (4 TMS) domain K+ channel, TREK-2 (KCNKA) (activated by membrane stretch, acidic pH, arachidonic acid and unsaturated fatty acids.)
TREK-2 of Rattus norvegicus

The TWiK family muscle K+ channel protein 18 (TWiK or Two-P domain K+ channel family) (controls muscle contraction and organismal movement; Kunkel et al., 2000)
TWK-18 of Caenorhabditis elegans

The pH-sensitive 2 pore (4 TMS) K+ channel, TASK-4 (Expressed in liver, lung, pancreas and other tissues; Decher et al., 2001). The response of the tandem pore potassium channel TASK-3 (K(2P)9.1) to voltage involves gating at the cytoplasmic mouth (Ashmole et al., 2009). Models have revealed the convergence of amino acid regions that are known to modulate anesthetic activity onto a common three- dimensional cavity that forms a putative anesthetic binding site in tandem pore potassium channels (Bertaccini et al. 2014).


TASK-4 of Homo sapiens

Sup-9 K+ channel (possibly regulated by unc-93; and may be a suppressor of unc-93. Another regulator of Sup-9 is Sup-10 (Q17374) (de la Cruz et al., 2003).


Sup-9 of Caenorhabditis elegans (O17185)

TWiK family of potassium channels protein 9
twk-9 of Caenorhabditis elegans

TWiK family of potassium channels protein 12
Twk-12 of Caenorhabditis elegans

Potassium channel subfamily K member 16 (2P domain potassium channel Talk-1) (TWIK-related alkaline pH-activated K(+) channel 1) (TALK-1)
KCNK16 of Homo sapiens

Voltage-sensitive Na+ channel, NaV1.7 (Cox et al., 2006). The human orthologue, SCN3A when mutated causes cryptogenic pediatric partial epilepsy (Holland et al., 2008)


Voltage-sensitive Na+ channel of Rattus norvegicus

Na+ channel, α-subunit, SCAP1
SCAP1 from Aplysia californica (P90670)

Ca2+-regulated heart Na+ channel, Nav1.5 or SCN5A of 2016 aas (the COOH terminus functions in the control of channel inactivation and in pathologies caused by inherited mutations that disrupt it (Glaaser et al., 2006)); regulated by ProTx-II Toxin (Smith et al. 2007), telethonin, the titin cap protein; 167aas; secreted protein; O15273) (Mazzone et al., 2008), and the Mog1 protein, a central component of the channel complex (Wu et al., 2008). Nav1.5, the principal Na+ channel in the heart, possesses an ankyrin binding site; direct interaction with ankyrin-G is required for the expression of Nav1.5 at the cardiomyocyte cell surface (Bennett and Healy, 2008; Lowe et al., 2008). Mutations cause type 3 long QT syndrome and type 1 Brugada syndrome, two distinct heritable arrhythmia syndromes (Mazzone et al., 2008; Kapplinger et al. 2010). SCN5A mutations causing arrhythmic dilated cardiomyopathy, commonly localized to the voltage-sensing mechanism, and giving rise to gating pore currents (currents that go through the voltage sensor) have been identified (McNair et al., 2011; Moreau et al., 2014).  Patients with Brugada syndrome are prone to develop ventricular tachyarrhythmias that may lead to syncope, cardiac arrest or sudden cardiac death (Sheikh and Ranjan 2014).


Nav1.5 of Homo sapiens (Q14524)

The skeletal muscle Na+ channel, NaV1.4 (mutations in the S4 segment cause hypokalemic periodic paralysis; Sokolov et al., 2007; Groome et al. 2014). Also causes myotonia; regulated by calmodulin which binds to the C-terminus of Nav1.4 (Biswas et al., 2008). NaV1.4 gating pores are permeable to guanidine (Sokolov et al., 2010). 


NaV1.4 of Homo sapiens (P35499)

Voltage-sensitive Na channel, type 9, α-subunit, Nav1.7 or SCN9A (orthologous to 1.A.1.10.1). Loss of function results in a channelopathy that causes the congenital inability to experience pain (Cregg et al., 2010; Kleopa, 2011). An S241T mutation causes inherited erythromelalgia IEM; erythermalgia, an autosomal dominant neuropathy characterized by burning pain in the extremities in response to mild warmth (due to altered gating) (Lampert et al., 2006; Drenth and Waxman, 2007). Gain-of-function mutations in the Na(v)1.7 channel lead to DRG neuron hyperexcitability associated with severe pain, whereas loss of the Na(v)1.7 channel in patients leads to indifference to pain (Dib-Hajj et al., 2007). Blocked by 1-benzazepin-2-one (Kd = 1.6 nM) (Williams et al., 2007). Mutations in the Nav1.7 Na channel α-subunit give rise to familial pain syndromes called chronic non-paoxysmal neuropathic pain (Catterall et al., 2008; Fischer and Waxman, 2010; Dabby et al. 2011 ).


Nav1.7 of Homo sapiens (Q15858)

Tetrodotoxin-resistant voltage-gated Na+ channel of dorsal ganglion sensory neurons, Nav1.8 (Akopian et al., 1996). Essential for pain at low temperatures (Zimmermann et al., 2007). Nav1.8 is the sole electrical impulse generator in a nociceptor that transmits information to the central nervous system.  Bark scorpion venom induces pain in many mammals (house mice, rats, humans) by activating Nav1.7 but has no effect on Nav1.8. Grasshopper mice Nav1.8 has amino acid variants that bind bark scorpion toxins and inhibit Na+ currents, blocking action potential propagation and inducing analgesia.  These mice thereby can use scorpions as a food source (Zhu et al. 2013; Rowe et al. 2013).


Nav1.8 of Rattus norvegicus

Voltage-sensitive Na+ channel, Nav1.1 or SCN1A (causes epilepsy when mutated) (Rusconi et al., 2007).
Nav1.1 of Homo sapiens (P35498)

The Voltage-gated Na+ channel α-subunit, Nav1.6, encoded by the Scn8a gene which when defective gives rise to the ENU-induced neurological mutant ataxia3 which gives rise to ataxia, tremors, and juvenile lethality.   75% identical to 1.A.1.10.7. Nav1.6 is the dendritic, voltage-gated sodium channel (responsible for dendritic excitability (Lorincz and Nusser, 2010)). Nav1.6 (SCN8A) interacts with microtubule-associated protein (O'Brien et al., 2012). Scorpion alpha toxins bind at receptor site-3 and inhibit channel inactivation, whereas beta toxins bind at receptor site-4 and shift the voltage-dependent activation toward more hyperpolarizing potentials (Gurevitz, 2012).  Mutations give rise to epileptic encephalopathy and intellectual disability (O'Brien and Meisler 2013).  A gain-of-function mutation gave rise to increased channel activation and infantile epileptic encephalopathy (Estacion et al. 2014).


Nav1.6 of Homo sapiens (Q9UQD0)

The voltage-gated Na+ channel α-subunit, Nav1.9. Present in excitable membranes. Resistant to tetrodotoxin (Bosmans et al., 2011).


Nav1.9 of Homo sapiens (Q9UI33)

The insect (cockroach) Na   channel. Batrachotoxin, pyrethroids, and BTG 502 share overlapping binding sites (Du et al., 2011).  Insecticides tagetting Na+ channels include indoxacarb and metaflumizone (Casida and Durkin 2013).  Asp802 is involved in gating and action, but not binding, of pyrethroid insecticides (Du et al. 2010).


Na+ channel of Blattella germanica (O01307)

Sodium channel of 2215 aas, VmNa.  An L925V mutation in the channel domain renders the honey bee mites resistant to pyrethroids such as tau- fluvalinate and flumethrin (González-Cabrera et al. 2013).


Animals (Insects)

VmNa of Varroa destructor

Type 2 Na+ channel, SCN2A of 2,005 aas.  Mutations give rise to epileptic encephalophathy, Ohtahara syndrome (Nakamura et al. 2013).  This protein is orthologous to the rat Na+ channel, TC# 1.A.1.10.1 and very similar to the type 1 Na+ channel (1.A.1.10.7).


SCN2A of Homo sapiens

Voltage-sensitive Na+ channel of 2821 aas and 24 TMSs (Cohen et al. 2009).


Na+ channel of Drosophila melanogaster

Voltage-sensitive Ca2+ channel (transports Ca2+, Ba2+ and Sr2+)
Voltage-sensitive Ca2+ channel, α-1 chain of Rattus norvegicus

Muscle plasmalemma, voltage-gated, L-type dihydropyridine receptor Ca2+ channel, α-1 subunit (DHPR) (Ba2+ > Ca2+)
DHPR of Oryctolagus cuniculus

Voltage-dependent R-type Ca2+ channel, α-1E subunit (Cav2.3) (brain Ca2+ channel type II) (Ca2+ > Ba2+). Interacts with V-type ATPases (3.A.2), specifically, the G1-subunit to regulate function (Radhakrishnan et al., 2011).


R-type Ca2+ channel of Mus musculus

The voltage-dependent L-type Ca2+ channel α-subunit-1C (L-type Cav1.2), CACNA1C (mutations cause Timothy's syndrome, a disorder associated with autism) (Splawski et al., 2006). The C-terminus of Cav1.2 encodes a transcription factor (Gomez-Ospina et al., 2006). Cav1.2 associates with the α-2, δ-1, β and γ subunits (Yang et al., 2011). The CRAC channel activator STIM1 binds and inhibits L-type voltage-gated calcium channel, Cav1.2 (Park et al., 2010).  This channel appears to function as the molecular switch for synaptic transmission (Atlas 2013). Intramembrane signalling occurs with syntaxin 1A for catecholamine release in chromaffin cells (Bachnoff et al. 2013).


CACNA1C of Homo sapiens (2221 aas; Q13936)

The voltage-dependent L-type Ca2+ channel α-subunit-1H (T-type Cav3.2), CACNA1H (mutations can cause an increased propensity for autism spectrum disorders (ASD) characterized by impaired social interactions, communication skills and restricted and repetitive behaviors) (Splawski et al., 2006). Also called Cav3.2 or VSCC. Involved in a variety of calcium-dependent processes, including muscle contraction, hormone or neurotransmitter release, gene expression, cell motility, cell division and cell death. The isoform alpha-1H gives rise to T-type calcium currents, ''low-voltage activated'' currents blocked by nickel and mibefradil. Defective in Childhood Absence Epilepsy. Are permeated by divalent metal ions, such as Fe2 and Mn2 , and possibly Cd2 (Thévenod, 2010).  Patented inhibitors of T-type calcium channels have been reviewed (Giordanetto et al. 2011).


CACNA1H of Homo sapiens (2353 aas; Q95180)

Voltage-dependent L-type Ca2+ channel subunit α-1C (αCav1.2) of cardiac muscle [A C-terminal fragment of Cav1.2 translocates to the nucleus and regulates transcription, explaining how a channel can directly activate transcription and differentiation of excitable cells.] (Gomez-Ospina et al., 2006). Cav1.2 associates with the α-2, δ-1, β and γ subunits (Yang et al., 2011).


α-Cav1.2 of Mus muscultus (2139 aas; Q01815)

The voltage-dependent Ca2+ channel subunit α-1I (isoform CRA_c (2188 aas))


Ca2+ channel CRA_c of Homo sapiens (EAW60347) (B0QY14)

Voltage-dependent Ca2+ channel α-1A subunit (2212 aas), Cav2.1 (P/Q-type) (when mutated in humans, leads to a human channelopathy (episodic ataxia type-2 (EA2)) due to protein misfolding and retention in the E.R. (Mezghrani et al., 2008; Kleopa, 2011).  Mutations give rise to familial and sporadic hemiplegic migraine type 1 (FHM1, SHM1), episodic ataxia type 2 (EA2), and spinocerebellar ataxia type 6 (SCA6) (García Segarra et al. 2014).Syntaxin 1A (Sx1A), SNAP-25 and synaptotagmin (Syt1), either alone or in combination, modify the kinetic properties of voltage-gated Ca2+ channels (VGCCs) including Cav2.1 (Cohen-Kutner et al. 2010).


Cav2.1 of Rattus norvegicus (P54282)

Voltage-dependent Ca2+ channel -subunit 1B (2339 aas), Cav2.2 (N-type). Anchorin B interacts with Cav2.2 in the loop between TMSs 2 and 3.  TSPAN-13 specifically interacts with the α-subunit and modulates the efficiency of coupling between voltage sensor activation and pore opening of the channel while accelerating the voltage-dependent activation and inactivation of the Ba2+ current through CaV2.2 (Mallmann et al. 2013).


Cav2.2 of Mus musculus (O55017)

Plasma membrane voltage-gated, high affinity Ca2+ channel, Cch1/Mid1; activated by mating pheromones and environmental stresses; required for growth in low Ca2+ (Locke et al., 2000; Paidhungat and Garrett, 1997). Also essential for tolerance to cold stress and iron toxicity (Peiter et al., 2005). Ecm7, (448aas; 4 TMS; TC# 1.H.1.4.6), a member of the PMP-22/EMP/MP20 Claudin superfamily of transmembrane proteins that includes gamma-subunits of voltage-gated calcium channels appears to interact with Mid1 TC# 8.A.41.1.1) and regulate the activity of the Cch1/Mid1 channel (Martin et al., 2011). Ecm7p is related to members of TC families 1.H.1, 1.H.2 and 1.A.81.


Cch1/Mid1 of Saccharomyces cerevisiae
Cch1 (P50077)
Mid1 (P41821)
Ecm7p (Q06200) 

The Cav1.4 Ca2+ channel (gene CACNA1F). Mutations resulting in increased activity cause x-linked incomplete congenital stationary night blindness (CSNB2) (Hemara-Wahanui et al., 2005; Peloquin et al., 2007).


Cav1.4 of Homo sapiens

T-type Ca2+ channel (Cav3.1d) in developing heart (fetal myocardium (Cribbs et al., 2001). Both Cav3.1 and Cav3.2 are permeated by divalent metal ions, such as Fe2+ and Mn2+, and possibly Cd2+ (Thévenod, 2010).  CaV3.1 channels are activated at low votage and regulate neuronal excitability in the spinal cord (Canto-Bustos et al. 2014).


Cav3.1d of Mus musculus (Q9WUT2)

Two-pore Ca2+ channel protein 1, TPC1 (Km(Ca2+))=50 µM; voltage gated; 461 aas; 6TMSs) (Hashimoto et al., 2004; Kurusu et al, 2004; 2005)
TPC1 of Oryza sativa (Q5QM84)

Voltage-dependent calcium channel, α-1 subunit (1911aas), CyCaα1
CyCaα1 of Cyanea capillata (O02038)

Neuronal nonselective cation channel, NALCN (forms background leak conductance and controls neuronal excitability; Lu et al., 2007).  It is also found in the pancreatic β-cell (Swayne et al. 2010). NALCN serves as a variable sensor that responds to calcium or sodium ion flux, depending on whether the total cellular current density is generated more from calcium-selective or sodium-selective channels (Senatore and Spafford 2013).


NALCN of Homo sapiens (Q6P2S6)

4 domain-type voltage-gated ion channel, α-1 subunit NCA-2 (Jospin et al., 2007) (dependent on Unc-80 (3225aas; CAB042172) for proper localization).
NCA-2 of Caenorhabditis elegans (Q06AY4)

The high affinity Ca2+ channel; associates with elongation factor 3 (EF3) to target Cch1/Mid1 to the plasma membrane (Liu and Gelli, 2008).


Cch1/Mid1 of Cryptococcus neoformans
Cch1 (Q1HHN2)
Mid1 (Q5KM96) 

The nicotinic acid adenine dinucleotide phosphate (NAADP)- dependent two pore Ca2+- channel, TPC3 (Brailoiu et al., 2010).


Two pore Ca2+ channel 3, TPC3 of Bos taurus (C4IXV8)

The phosphoinositide (PI(3,5)P2)-activated Na+ two pore channel-2, TPC2, in endosomes and lysosomes (Wang et al. 2012). Previously thought, incorectly, according to Wang et al. 2012, to be a nicotinic acid adenine dinucleotide phosphate (NAADP)-dependent two pore Ca2+ channel.  TPC2, like TPC1, has a 12 TMS topology (two channel units) (Hooper et al., 2011). The two domains of human TPCs can insert into the membrane independently (Churamani et al., 2012).  Cang et al. (2013), showed that TPC1 and TPC2 together form an ATP-sensitive two-pore Na+ channel that senses the metabolic state of the cell.  The channel complex detects nutrient status, becomes constitutively open upon nutrient removal, and controls the lysosome's membrane potential, pH stability, and amino acid homeostasis.  Essential for Ebola virus (EBOV) host entry. Several inhibitors of TPC2 that act in the nM (tetrandrine) or μM (verapamil; Ned19) range block channel activity, prevent Ebola Virus from escaping cell vesicles and may be used to treat the disease (Sakurai et al. 2015).  TPC2 may transport both Na+ and Ca2+ (Sakurai et al. 2015).


TPC2 of Homo sapiens (Q8NHX9)

The voltage-gated Ca2+ channel, L-type α-subunit, Eg1-19 regulated by Macoilin (8.A.38.1.2)


Eg1-19 of Caenorhabditis elegans (A8PYS5)

Voltage-gated Ca2+ channel, Egl-19, isoform a


Egl-19 of C. elegans (G5EG02)

The phosphoinositide (PI(3,5)P2)-activated Na+two pore+channel-1, TPC1 of endosomes and lysosomes (Wang et al. 2012). Previously thought, incorectly, according to Wang et al. (2012), to be an NAADP-activated two pore voltage-dependent calcium channel protein.  However, Cang et al. (2013), showed that TPC1 and TPC2 (TC# 1.A.1.11.19) together form an ATP-sensitive two-pore Na channel that senses the metabolic state of the cell.  The channel complex detects nutrient status, becomes constitutively open upon nutrient removal, and controls the lysosome''s membrane potential, pH stability, and amino acid homeostasis.  May be regulated by the HCLS-associated X-1 (HAX-1) protein (Lam et al. 2013).


Tpcn1 of Mus musculus

Cch1 calcium channel, alpha subunit; acts with Mid1 (8.A.41.1.7) which is required for function.


Mid1 of Schizosaccharomyces pombe

Voltage-sensitive calcium channel of 2693 aas (Docampo et al. 2013).

Euglenozoa (Protozoa)

Calcium channel of Trypanosoma brucei

Two pore Na+ channel protein of 816 aas and 12 TMSs, TPC1 or TPCN1.  Endosomes and lysosomes are electrically excitable organelles (Cang et al. 2014). In a subpopulation of endolysosomes, a brief electrical stimulus elicits a prolonged membrane potential depolarization spike. The organelles have a depolarization-activated, noninactivating Na+ channel (lysoNaV). The channel is formed by a two-repeat six-transmembrane-spanning (2x6 TMS) protein, TPC1, which represents the evolutionary transition between 6 TMS and 4x6 TMS voltage-gated channels. Luminal alkalization also opens lysoNaV by markedly shifting the channel's voltage dependence of activation toward hyperpolarization. Thus, TPC1 is a voltage-gated Na+ channel that senses pH changes and confers electrical excitability to organelles (Cang et al. 2014). Essential for Ebola virus (EBOV) host entry.  Several inhibitors act in the nM (tetrandrine) or μM (verapamil; Ned19) range to block Na+ and Ca2+ channel activity, inhibit virus escape from membrane vesicles and may possibly be used to treat the disease (Sakurai et al. 2015).


TPC1 of Homo sapiens

Two pore Na+ channel protein of 733 aas, TPC1.


TPC1 of Arabidopsis thaliana

Voltage-dependent P/Q-type Ca2+ channel subunit α1A, CACNA1A (CACH4; CACN3; CACNL1A4) of 2,505 aas.  90% identical to 1.A.1.11.8.  Associated with three neurological phenotypes: familial and sporadic hemiplegic migraine type 1 (FHM1, SHM1), episodic ataxia type 2 (EA2), and spinocerebellar ataxia type 6 (SCA6). A gain of function mutation gave symptoms of congenital ataxia, abnormal eye movements and developmental delay with severe attacks of hemiplegic migraine (García Segarra et al. 2014).


CACNA1A Ca2+ channel of Homo sapiens

Paramecium bursaria Chlorella virus 1 (PBCV-1) K+ channel, Kcv1. (The viral-encoded K+ channel inserts into the green algal host membrane to aid ejection of DNA from the viral particle into the cytoplasm (Neupartl et al., 2007)). It may mediate host cell membrane depolarization and K+ loss (Agarkova et al., 2008; Balss et al., 2008).  It is inhibited by Ba2+ and amantidine. (Reviewed by Thiel et al., 2010).


Kcv1 K+ channel of Chlorella virus PBCV-1

Acanthocystis turfacea chlorella virus cation (K+)-preferring channel, ATCV1 (82aas) (Gazzarrini et al., 2009; Siotto et al. 2014).

Algal virus

ATCV1 of Acanthocystis turfacea chlorella virus (A7K9J5)

The viral K+channel, Kesv of 124 aas.  It is inhibited by Ba2+ and amantidine.  It is important for infection and replication in marine brown algae (Chen et al. 2005; Balss et al., 2008; Siotto et al. 2014).


Kesv of Ectocarpus siliculosus virus 1 (Q8QN67)

Viral K+ channel of 96 aas and 2 TMSs, Kcv (Siotto et al. 2014).


Kcv of Paramecium bursaria Chlorella virus

6TMS K+ channel (Kuo et al., 2003).  The kch gene, the only known potassium channel gene in E. coli, has the property to express both full-length Kch and its cytosolic domain (RCK) due to a methionine at position 240. The RCK domains form an octameric ring structure and regulate the gating of the potassium channels after having bound certain ligands. Several different gating ring structures have been reported for the soluble RCK domains.  The octameric structure of Kch may be composed of two tetrameric full-length proteins through RCK interaction (Kuang et al. 2013).

Gram-negative bacteria

Kch of E. coli

2 TMS ( P-loop) Ca2 -gated K channel, MthK (see Jiang et al., 2002 for the crystal structure, and Parfenova et al., 2006 for mutations affecting open probability. For the studies of ion permeation and Ca2 blockage, see Derebe et al., 2011). (structures: 3LDD_A; 2OGU_A.). Voltage-dependent K channels including MthK which lacks a canonical voltage sensor can undergo a gating process known as C-type inactivation, which involves entry into a nonconducting state through conformational changes near the channel''s selectivity filter (Thomson and Rothberg, 2010). C-type inactivation may involve movements of transmembrane voltage sensor domains.



MthK of Methanothermobacter thermoautotrophicus (O27564)

Divalent cation (Ca2+, Mg2+, Mn2+, Ni2+)-activated K+ channel, TuoK (contains a RCK domain) (Parfenova et al., 2007)


TuoK of Thermoplasma volcanium (Q979Z2)  

The Biofilm-inducing putative K+ channel, BikC or YugO (M. Lunderg, personal communication). BikC has an N-terminal 2 TMS + P-loop channel domain and a C-terminal NADB_Rossman superfamily domain. YugO is in a two cistronic operon where Mistic (MstX; 9.B.23; Debnath et al., 2011; Roosild et al., 2005) is encoded by the gene that precedes YugO. Both play a role in biofilm formation, probably by functioning together (M. Lundberg, personal communication).


BikC of Bacillus subtilis (Q795M8)

Putative 2 TMS ion channel protein (N-terminus) with C-terminal TrkA_N (NADB Rossman) domain.


Ion channel protein of Streptomyces coelicolor

Ca2+-activated K+ channel, SynCaK. Functions in the regulation of photosynthesis (Checchetto et al. 2013; Checchetto et al. 2013).


K+ channel of Synechocystis PCC6803

PUtative K+ channel


K+ channel of Synechocystis PCC6803

Voltage-activated, Ca2 channel blocker-inhibited, Na channel, NaChBac (Ren et al., 2001; Zhao et al., 2004Nurani et al, 2008; Charalambous and Wallace, 2011). Transmembrane and extramembrane contributions to thermal stability have been studied (Powl et al., 2012). Deprotonation of arginines in S4 is involved in NaChBac gating (Paldi, 2012). Hinge-bending motions in the pore domain of NaChBac have been reported (Barber et al., 2012).  The C-terminal coiled-coli stabilizes subunit interactions (Mio et al. 2010).  Within the 4 TMS voltage sensor, coupling between residues in S1 and S4 determines its resting conformation (Paldi and Gurevitz 2010).

Gram-positive bacteria

NaChBac of Bacillus halodurans

Voltage-gated Na+ channel, NavPZ (Koishi et al., 2004)
Gram-negative bacteria
NavPZ of Paracoccus zeaxanthinifaciens (CAD24429)

Na+ channel, NavBP, involved in motility, chemotaxis and pH homeostasis (Ito et al., 2004). NavBP colocalizes with a methyl-accepting chemotaxis protein (MCP) at the cell poles (Fujinami et al., 2007).
NavBP of Bacillus pseudofirmus (AAT21291)

Voltage-gated Na+ channel, VGSC (Koishi et al., 2004; McCusker et al., 2011) Changing the selectivity filter from LESSM to LDDWSD yielded a Calcium-selective channel (Shaya et al., 2011).


VGSC of Silicibacter pomeroyi (56676695)

Voltage-gated Na+ channel, NavCh. 3d-structure known (3ROW; Payandeh et al., 2011). An anionic coordination site was proposed to confer Na+ selectivity through partial dehydration of Na+ via its direct interaction with conserved glutamate side chains. The pore is preferentially occupied by two ions, which can switch between different configurations by crossing low free-energy barriers (Furini and Domene, 2012).


NavCh of Arcobacter butzleri (A8EVM5)

Bacterial voltage-gated sodium channel, Nav.  The 3-d crystal structure of the open-channel conformation is known (McCusker et al. 2012).  It has its internal cavity accessible to the cytoplasmic surface as a result of a bend/rotation about a central residue in the carboxy-terminal TMS that opens the gate to allow entry of hydrated sodium ions. The molecular dynamics of ion transport through the open conformation has been analyzed (Ulmschneider et al. 2013).  The C-terminal four helix coiled coil bundle domain couples inactivation with channel opining, depedent on the negatively charged linker region (Bagnéris et al. 2013).


Nav of Magnetococcus marinus (also called sp. strain MC-1)

Tetrameric 6 TMS subunit Na+ channel protein, NaV.  Two low resolution cyroEM structures revealed two conformations reconstituted in lipid bilayers (Tsai et al. 2013). Despite a voltage sensor arrangement identical with that in the activated form, Tsai et al. 2013 observed two distinct pore domain structures: a prominent form with a relatively open inner gate, and a closed inner-gate conformation similar to the first prokaryotic Nav structure. Structural differences, together with mutational and electrophysiological analyses, indicated that widening of the inner gate was dependent on interactions among the S4-S5 linker, the N-terminal part of S5 and its adjoining part in S6, and on interhelical repulsion by a negatively charged C-terminal region subsequent to S6 (Tsai et al. 2013).


Nav of Caldalkalibacillus thermarum

6 TMS basolateral tracheal epithelial cell/voltage-gated, small conductance, K+ α-chain) [acts with the KCNE3 β-chain]. Mutations in human Kv7 genes lead to severe cardiovascular and neurological disorders such as the cardiac long QT syndrome and neonatal epilepsy (Haitin and Attali, 2008). KCNE3 can co-assemble with KCNQ1 (1.A.1.15.6) (Kang et al., 2010). KCNQ1 regulates insulin secretion in  the MIN6 beta-cell line (Yamagata et al., 2011).  The S4-S5 linker of KCNQ1 forms a scaffold with S6 controlling gate closure (Labro et al. 2011).  The KCNQ1 channel is differentially regulated by KCNE1 and KCNE2 (Li et al. 2014).


KCNQ1 K+ channel of Mus musculus

    6 TMS voltage-gated K channel, KCNQ2 or Kv7.2.  Mutations cause benign familial neonatal convulsions (BNFC; epilepsy).  It forms homotetramers or heterotetramers with KCNQ3/Kv7.3) (Soldovieri et al., 2006; Uehara et al., 2008)). Like all other Kv7.2 channels, it is activated by phosphatidyl inositol-4,5-bisphosphate and hence can be regulated by various neurotransmitters and hormones (Telezhkin et al. 2013).  Gating pore currents that go through the gating pores in TMSs1-4 (the voltage sensor) may give rise to peripheral nerve hyperexcitability (Moreau et al. 2014).


KCNQ2 K+ channel of Homo sapiens (O43526)

   6 TMS voltage-gated K+ channel, KCNQ3 (mutations cause benign familial neonatal convulsions (BNFC; epilepsy)) (forms homotetramers or heterotetramers with KCNQ2) (Soldovieri et al., 2006; Uehara et al., 2008)


KCNQ3 K+ channel of Homo sapiens (O43525)

   6 TMS cell volume sensitive, voltage-gated K+ channel, KCNQ4 or Kv7.4 (mutations cause DFNA2, an autosomal dominant form of progressive hearing loss) (forms homomers or heteromers with KCNQ3) (localized to the basal membrane of cochlear outer hair cells and in several nuclei of the central auditory pathway in the brainstem). Four splice variants form heterotetramers; each subunit has different voltage and calmodulin-sensitivities (Xu et al., 2007).  Autosomal dominant mutant forms leading to progressive hearing loss (DFNA2) have been characterized (Kim et al. 2011).


KCNQ4 K+ channel of Homo sapiens

The KCNQ5 K channel (modulated by Zn2 , pH and volume change) (Jensen et al., 2005).  A triple cysteine module within M-typ K+ channels mediates reciptrocal channel modulation by nitric oxide and reactive oxygen species (Ooi et al. 2013).


KCNQ5 of Mus musculus

K+ voltage-gated channel, KQT-like subfamily; Kv7.1; KvLQT1; KCNQ1 (regulated by KCNE peptides which affect voltage sensor equilibrium; Rocheleau and Kobertz, 2007). Almost 300 mutations of KCNQ1 have been identified in patients, and most are linked to the long QT syndrome (LQT1) (Peroz et al., 2008; Eldstrom et al. 2010; Qureshi et al. 2013). KCNQ1-KCNE1 complexes may interact intermittently with the actin cytoskeleton via the C-terminal region (Mashanov et al., 2010). The stoichiometry of the KCNQ1 - KCNE1 complex is flexible, with up to four KCNE1 subunits associating with the four KCNQ1 subunits of the channel (Nakajo et al., 2010). A familial mutation in the voltage-sensor of the KCNQ1 channel results in a cardiac phenotype (Henrion et al., 2012). KCNQ1 regulates insulin secretion in the MIN6 beta-cell line (Yamagata et al., 2011; Gofman et al., 2012).  Electrostatic interactions of S4 arginines with E1 and S2 contribute to gating movements of S4, but coupling requires the lipid phosphatidylinositol 4,5-bisphosphate (PIP2) as voltage-sensing domain activation failed to open the pore in the absence of PIP2 (Eldstrom et al. 2010; Qureshi et al. 2013). KCNQ1-KCNE1 complexes may interact intermittently with the actin cytoskeleton via the C-terminal region (Mashanov et al., 2010). The stoichiometry of the KCNQ1 - KCNE1 complex is flexible, with up to four KCNE1 subunits associating with the four KCNQ1 subunits of the channel (Nakajo et al., 2010). A familial mutation in the voltage-sensor of the KCNQ1 channel results in a cardiac phenotype (Henrion et al., 2012). KCNQ1 regulates insulin secretion in the MIN6 beta-cell line (Yamagata et al., 2011; Gofman et al., 2012).  Electrostatic interactions of S4 arginines with E1 and S2 contribute to gating movements of S4, but coupling requires the lipid phosphatidylinositol 4,5-bisphosphate (PIP2) as voltage-sensing domain activation failed to open the pore in the absence of PIP2 (Zaydman et al. 2013). 



KCNQ1 of Homo sapiens (P51787)

The small conductance Ca2+-activated K+ channel, SkCa2 (not inhibited by arachidonate) (activated by three small organic molecules, the 1-EBIO and N5309 channel enhancers and the DCEBIO channel modulation (Pedarzani et al., 2005)).  It is inhibited by protonation of outer pore histidine residues (Goodchild et al., 2009). The same is true for SK3 (K(Ca) 2.3 (Q9UGI6)). Regulates endothelial vascular function (Sonkusare et al., 2012).


SkCa2 of Homo sapiens

The intermediate conductance, Ca2+-activated K+ channel, hIK1 (inhibited by 1 μM arachidonate which binds in the pore (Hamilton et al., 2003). Nucleoside diphosphate kinase B (NDPK-B) activates KCa3.1 via histidine phosphorylation, resulting in receptor-stimulated Ca2+ flux and T cell activation (Di et al., 2010). Regulates endothelial vascular function (Sonkusare et al., 2012).  Tissue-specific expression of splice variant of the orthologous rat KCNN4 protein have been reported (Barmeyer et al. 2010).  Residues involved in gating have been identified (Garneau et al. 2014).


hIK1 of Homo sapiens (AAC23541)

Small conductance calcium-gated potassium (SK) channel. Three charged residues in TMS S6 of SK channels near the inner mouth of the pore collectively control the conductance and rectification through an electrostatic mechanism (Li and Aldrich, 2011).


SK of Drosophila melanogaster (Q7KVW5)

Small conductance Ca2+-activated K+ channel, KCNL-2 of 672 aas. Plays a role in the rate of egg laying (Chotoo et al. 2013).


KCNL-2 of Caenorhabditis elegans

Plasma membrane small conductance calcium-activated K+ channel of 396 aas, TSKCa; probably involved in immunoregulation (Cong et al. 2009).

Animals (fish)

TSKCa of Psetta maxima (Turbot) (Pleuronectes maximus)

The archaeal voltage-regulated K channel, KvAP (Ruta et al., 2003). X-ray and solution structures are available. The latter shows phospholipid interactions with the isolated voltage sensor domain (Butterwick and MacKinnon 2010; Li et al. 2014). The gating-charge arginine in TMS4 of the voltage sensor forms part of the helical hairpin "paddle", and it moves 15-20 Å through the membrane to open the pore (Ruta et al., 2005). The orientation and depth of insertion of the voltage-sensing S4 helix has been determined (Doherty et al., 2010). A synthetic S6 segment derived from the KvAP channel self-assembles, permeabilizes lipid vesicles, and exhibits ion channel activity in bilayer lipid membrane (Verma et al., 2011).  Thus the gating mechanism combines structural rearrangements and electric-field remodeling ( Li et al. 2014).  KvAP has been reconstituted in Giant Unilamellar Vesicles (GUVs) (Garten et al. 2015).


KvAP of Aeropyrum pernix (Q9YDF8) 

Voltage-gated K+ channel, Kv (Santos et al., 2008).


Kv of Listeria monocytogenes (Q8Y5K1)

The two-pore domain potassium channel, TRESK-1 (Czirjak et al., 2004) (provides the background K+ current in mouse DRG neurons (Dobler et al., 2007)) TRESK (TWIK-related spinal cord K+ channel) is reversibly activated by the calcium/calmodulin-dependent protein phosphatase, calcineurin, and Czirjak et al. (Czirjak et al. 2008) reported that 14-3-3 proteins which directly bind to the intracellular loop to TRESK and control the kinetics of the calcium-dependent regulation. Cloxyquin (5-chloroquinolin-8-ol) is an activator (Wright et al. 2013).  A cytoplasmic loop binds tubulin (Enyedi et al. 2014).


TRESK-1 of Mus musculus (AAQ91836)

Alkalinizatioin-activated Ca2 -selective channel, sperm-associated cation channel, CatSper, required for male fertility and the hyperactivated motility of spermatozoa. These channels require auxiliary subunits, CatSperβ, γ and %u03B4 for activity (Chung et al., 2011).  The primary channel protein is CatSper1 (Liu et al., 2007).


CatSper of Homo sapiens
CatSper1 (Q96P76)
CatSper3 (Q86XQ3)
CatSper4 (Q7RTX7)
CatSperβ (Q9H7T0)
CatSperγ (Q6ZRH7)
CatSperδ (Tmem146) (Q86XM0) 

Sperm-associated cation channel, CatSper2 (6 TMS Ca2+ channel)
CatSper2 of Homo sapiens (26051223)

Alkalinization-activated Ca2 -selective channel, Cation channel of sperm 1, CatSper1, required for male fertility and the hyperactivated motility of spermatozoa. These channels require auxiliary subunits, CatSper β, γ and δ for activity (Chung et al., 2011; Liu et al., 2007).


CatSper of Mus musculus
CatSper1 (Q91ZR5)
CatSper3 (Q86XQ3)
CatSper4 (Q8BVN3)
CatSperβ (Q8C0R2)
CatSperγ (C6KI89)
CatSperδ (Tmem146) (E9Q9F6) 

K voltage-gated ether-a-go-go-related channel, H-ERG (KCNH2; Erg; HErg; Erg1) subunit Kv11.1 (long QT syndrome type 2) (Gong et al., 2006; Chartrand et al. 2010; McBride et al. 2013).  Forms a heteromeric K channel regulating cardiac repolarization, neuronal firing frequency and neoplastic cell growth (Szabó et al., 2011). Oligomerization is due to N-terminal interactions between two splice variants, hERG1a and hERG1b (Phartiyal et al., 2007).Structure funtion relationships of ERG channel activation and inhibition have been reviewed (Durdagi et al., 2010). Interactions between the N-terminal domain and the transmembrane core modulate hERG K channel gating (Fernández-Trillo et al., 2011). The marine algal toxin azaspiracid is an open state blocker (Twiner et al., 2012).  Hydrophobic interactions between the voltage sensor and the channel domain mediate inactivation (Perry et al. 2013).


H-ERG of Homo sapiens (Q12809)

Erg2 (Kv11.2) K+ channel with slowly activating delayed rectifier (expressed only in the nervous system) (Shi et al., 1997)
Erg2 of Rattus norvegicus

Erg3 (Kv11.3) K+ channel with a large transient current at positive potentials (expressed only in the nervous system) (Shi et al., 1997).
Erg3 of Rattus norvegicus

K+ voltage-gated channel, rEAG1; Kv 10.1; rat ether a go-go channel 1 (962 aas). Blocked by Cs+, Ba2+ and quinidine (Schwarzer et al., 2008). Cysteines control the N- and C-linker-dependent gating of KCNH1 potassium channels  (Sahoo et al., 2012).


EAG1 of Rattus norvegicus (Q63472)

Potassium voltage-gated channel subfamily H member 3 (Brain-specific eag-like channel 1) (BEC1) (Ether-a-go-go-like potassium channel 2) (ELK channel 2) (ELK2) (Voltage-gated potassium channel subunit Kv12.2)
KCNH3 of Homo sapiens

Cyclic nucleotide-binding, voltage-gated, Mg2 -dependent, CaMKII-regulated K channel, Eag.  Eag recruits CASK (TC# 9.B.106.3.2) to the plasma membrane; forms a heterotetramer (Liu et al. 2010).


Eag of Drosophila melanogaster

K+- and Na+-conducting NaK channel (3-D structure solves with Na+ and K+) (Shi et al., 2006)


NaK channel of Bacillus cereus (2AHYB) (Q81HW2)

The cyclic nucleotide-gated K+ channel, MmaK. (Activated by cyclic AMP and cyclic GMP; inactivated at slightly acidic pH (Kuo et al., 2007))
Gram-negative bacteria
MmaK of Magnetospirillum magnetotacticum (Q2W0I8)

The pea symbiosis protein, essential for nodulation, mycorrhization, and Nod-factor-induced calcium spiking, SYM8 or DMI1. (Most similar to 1.A.1.13.2; 894aas; 4 TMSs between residues 136 and 339) (Edwards et al., 2007)
SYM8 of Pisum sativum

Root nuclear envelope CASTOR: homomeric ion channel (preference of cations such as K+ over anions) (Charpentier et al., 2008) (62% identical to 1.A.1.23.1).


CASTOR of Lotus japonicus (Q5H8A6)

POLLUX homomeric ion channel (preference for cations over anions) (Charpentier et al., 2008) (81% identical to 1.A.1.23.1).


POLLUX of Lotus japonicus (Q5H8A5)

putative ion channel (N-terminal domain) protein with C-terminal TrkA-N domain (DUF1012); NAD-binding lipoprotein.


Ion channel protein of Streptomyces coelicolor

The cyclic nucleotide regulated K+ channel, CNR-K+ channel (412 aas)
CNR-K+ channel of Rhodopseudomonas palustris (Q02006)

K+ channel protein homologue 


K+ channels protein homologue of Stigmatella aurantiaca (Q08U57)

Putative 6 TMS potassium channel


Potassium ion channel of Myxococcus xanthus

Putative K+ channel


K channel of Cyanotheca (Synechococcus) sp PCC8801

Cyclic nucleotide-gated K+ channel of 459 aas.


Channel of Labenzia aggregata

The 6TMS bacterial cyclic nucleotide-regulated, voltage independent channel, MlotiK1 or MloK1 (Clayton et al., 2008). Gating involves large rearrangements of the cyclic nucleotide-binding domains (Mari et al., 2011).  The electron crystalographic structure is available (PDB 4CHW)revealing ligand-induced structural changes (Schünke et al. 2011; Scherer et al. 2014; Kowal et al. 2014). Such changes may be lipid dependent (Scherer et al. 2014; Kowal et al. 2014). Such changes may be lipid dependent (McCoy et al. 2014).


MlotiK1 of Mesorhizobium loti (Q98GN8)

The rodent malaria parasite K+ channel, PfKch1 (929aas) (Ellekvist et al., 2008).
Kch1 of Plasmodium berghei (Q4YNK7)

Putative 4 TMS ion channel protein.  TMSs 1-2 may not be homologous to TMSs 3-4 which probably form the channel.


Hypothetic VIC family member of Streptomyces coelicolor

Putative 4 TMS potassium ion channel protein.  TMSs 1-2 may not be homologous to TMSs 3-4 which probably form the channel.


Putative ion channel of Streptomyces coelicolor

Uncharacterized protein of 114 aas


UP of Rhizobium meliloti

Putative K+ channel


Putative K+ channel of Klebsiella varicola (D3RJS6)

Putative K+ channel


Putative K+ channel of Pseudomonas fluorescens (C3K1P0) 

Thylakoid membrane 6 TMS voltage-sensitive K+ channel, SnyK; important for photosynthesis (Checchetto et al. 2012).


SynK of Synechocystis sp.

Putative voltage-dependent K+ channel


K+ channel of Vibrio alginolytcus

Putative voltage-dependent K+ channel


K+ channel of E. coli

Putative voltage-dependent K+ channel


K+ channel of Acinetobacter baumannii

The 2 - 4 TMS K+ channel, LctB (Wolters et al. 1999).

Gram-positive bacteria

LctB of Bacillus stearothermophilus

Uncharacterized protein of 481 aas and 2 TMSs.  (Pfam CL0030)


UP of Pyrococcus furiosus