The transmembrane cation channel superfamily was defined in InterPro and Pfam as the family of tetrameric ion channels . These include the sodium , potassium ,[ 1] calcium , ryanodine receptor , HCN , CNG , CatSper , and TRP channels. This large group of ion channels apparently includes families 1.A.1 , 1.A.2 , 1.A.3 , and 1.A.4 of the TCDB transporter classification .
They are described as minimally having two transmembrane helices flanking a loop which determines the ion selectivity of the channel pore. Many eukaryotic channels have four additional transmembrane helices (TM) (Pfam PF00520 ), related to or vestigial of voltage gating . The proteins with only two transmembrane helices (Pfam PF07885 ) are most commonly found in bacteria. This also includes the 2-TM inward-rectifier potassium channels (Pfam PF01007 ) found primarily in eukaryotes. There are commonly additional regulatory domains which serve to regulate ion conduction and channel gating. The pores may also be homotetramers or heterotetramers ; where heterotetramers may be encoded as distinct genes or as multiple pore domains within a single polypeptide. The HVCN1 and Putative tyrosine-protein phosphatase proteins do not contain an expected ion conduction pore domain, but rather have homology only to the voltage sensor domain of voltage gated ion channels .
Human channels with 6 TM helices
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Transient receptor potential
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Voltage-gated potassium
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Kv α1.x - Shaker-related : Kv 1.1 (KCNA1 ), Kv 1.2 (KCNA2 ), Kv 1.3 (KCNA3 ), Kv 1.5 (KCNA5 ), Kv 1.6 (KCNA6 ), Kv 1.7 (KCNA7 ), Kv 1.8 (KCNA10 )
Kv α2.x - Shab-related: Kv 2.1 (KCNB1 ), Kv 2.2 (KCNB2 )
Kv α3.x - Shaw-related: Kv 3.1 (KCNC1 ), Kv 3.2 (KCNC2 )
Kv α7.x: Kv 7.1 (KCNQ1 ) - KvLQT1 , Kv 7.2 (KCNQ2 ), Kv 7.3 (KCNQ3 ), Kv 7.4 (KCNQ4 ), Kv 7.5 (KCNQ5 )
Kv α10.x: Kv 10.1 (KCNH1 )
Kv α1.x - Shaker-related: Kv 1.4 (KCNA4 )
Kv α3.x - Shaw-related: Kv 3.3 (KCNC3 ), Kv 3.4 (KCNC4 )
Kv α4.x - Shal-related: Kv 4.1 (KCND1 ), Kv 4.2 (KCND2 ), Kv 4.3 (KCND3 )
KCa 2.x: KCa 2.1 (KCNN1 ) - SK1, KCa 2.2 (KCNN2 ) - SK2, KCa 2.3 (KCNN3 ) - SK3
KCa 3.x: KCa 3.1 (KCNN4 ) - SK4
KCa 4.x: KCa 4.1 (KCNT1 ) - SLACK, KCa 4.2 (KCNT2 ) - SLICK
Inward-rectifier potassium
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Cyclic nucleotide-gated
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Human channels with 2 TM helices in each subunit
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Tandem pore domain potassium channel
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Ligand-gated potassium
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Voltage-gated potassium
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Voltage and cyclic nucleotide gated potassium
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Prokaryotic inward-rectifier potassium
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