Non-selective cation channel-2 family

Members of the Non-Selective Cation Channel-2 (NSCC2) Family (TC#1.A.15) have been sequenced from various yeast, fungal and animals species including Saccharomyces cerevisiae, Drosophila melanogaster and Homo sapiens.^[1] These proteins are the Sec62 proteins, believed to be associated with the Sec61 and Sec63 constituents of the general protein secretory systems of yeast microsomes. They are also the non-selective (NS) cation channels of the mammalian cytoplasmic membrane.

Function

NSCC2 channels are believed to provide entry pathways in response to growth factors.^[2] The yeast Sec62 protein has been shown to be essential for cell growth. The mammalian NS channel proteins have been implicated in platelet derived growth factor (PDGF)-dependent single channel current in fibroblasts. These channels are essentially closed in serum deprived tissue-culture cells and are specifically opened by exposure to PDGF.

The channels are reported to exhibit equal selectivity for Na⁺ , K⁺ and Cs⁺ with low permeability to Ca²⁺ , and no permeability to anions. Channel open probability is voltage- and cytoplasmic Ca²⁺-independent.

Transport reaction

The generalized transport reaction catalyzed by members of the NSCC2 family is:

Cation (out) ⇌ cation (in)

Structure and location

Sequenced NSCC2 family proteins are 283-402 amino acyl residues in length and exhibit two putative transmembrane α-helical segments (TMSs). The S. cerevisiae protein, of 283 amino acyl residues, has cytoplasmic N- and C-termini with two putative TMSs at positions 159-178 and 193-213. The C-terminal 25 residues are rich in arginine and lysine.^[1] These proteins have been reported to be present in both endoplasmic reticular and cytoplasmic membranes.