connexins

Connexins (Cx) (TC# 1.A.24), or gap junction proteins, are structurally related transmembrane proteins that assemble to form vertebrate gap junctions. An entirely different family of proteins, the innexins, forms gap junctions in invertebrates. Each gap junction is composed of two hemichannels, or connexons, which consist of homo- or heterohexameric arrays of connexins, and the connexon in one plasma membrane docks end-to-end with a connexon in the membrane of a closely opposed cell. The hemichannel is made of six connexin subunits, each of which consist of four transmembrane segments. Gap junctions are essential for many physiological processes, such as the coordinated depolarization of cardiac muscle, proper embryonic development, and the conducted response in microvasculature. Connexins also have non-channel dependant functions relating to cytoskeleton and cell migration. For these reasons, mutations in connexin-encoding genes can lead to functional and developmental abnormalities.

==Nomenclature== Connexins are commonly named according to their molecular weights, e.g. Cx26 is the connexin protein of 26 kDa. A competing nomenclature is the gap junction protein system, where connexins are sorted by their α (GJA) and β (GJB) forms, with additional connexins grouped into the C, D and E groupings, followed by an identifying number, e.g. GJA1 corresponds to Cx43. Following a vote at the Gap Junction Conference (2007) in Elsinore the community agreed to use the GJ nomenclature system for the genes that encode connexins, but wished to retain the connexin nomenclature for the encoded proteins using the weight of the human protein for the numbering of orthologous proteins.