Family 1.A.1 - The Voltage Gated Ion Channel Superfamily
Family ID: 52597
Proteins of the VIC family are ion-selective channel proteins
found in a wide range of bacteria, archaea and eukaryotes. They
are often homo- or heterooligomeric structures with several dissimilar
subunits (e.g., a1-a2-d-b Ca2+ channels, ab1b2Na+ channels or
(a)4-b K+ channels), but the channel and the primary receptor
is usually associated with the a (or a1) subunit. Functionally
characterized members are specific for K+, Na+ or Ca2+. The K+
channels usually consist of homotetrameric structures with each
a-subunit possessing six transmembrane spanners (TMSs). Many voltage-sensitive
K+ channels function with b-subunits that modify K+ channel gating.
These nonintegral b-subunits are oxidoreductases that coassemble
with the tetrameric a-subunits in the endoplasmic reticulum and
remain tightly adherent to the a subunit tetramer. The high resolution
b-subunit structure is available
The a1 and
a subunits of the Ca2+ and Na+ channels, respectively, are about
four times as large as the K+ channel a-subunits and possess 4
units, each with 6 TMSs separated by a hydrophilic loop, for a
total of 24 TMSs. These large channel proteins form heterotetra-unit
structures equivalent to the homotetrameric structures of most
K+ channels. All four units of the Ca2+ and Na+ channels are homologous
to the single unit in the homotetrameric K+ channels. Ion flux
via the eukaryotic channels is generally controlled by the transmembrane
electrical potential (hence the designation, voltage-sensitive)
although some are controlled by ligand or receptor binding.
