Protein Domain : Epithelial sodium channel, conserved site IPR020903

Type	Conserved_site
Description	The apical membrane of many tight epithelia contains sodium channels that are primarily characterised by their high affinity to the diuretic blockeramiloride [ , , , ]. These channels mediate the first step of active sodiumreabsorption essential for the maintenance of body salt and water homeostasis []. In vertebrates, the channels control reabsorption ofsodium in kidney, colon, lung and sweat glands; they also play a role in taste perception.Members of the epithelial Na +channel (ENaC) family fall into four subfamilies, termed alpha, beta, gamma and delta []. The proteins exhibitthe same apparent topology, each with two transmembrane (TM) spanning segments, separated by a large extracellular loop. In most ENaC proteinsstudied to date, the extracellular domains are highly conserved and contain numerous cysteine residues, with flanking C-terminal amphipathic TM regions,postulated to contribute to the formation of the hydrophilic pores of the oligomeric channel protein complexes. It is thought that the well-conservedextracellular domains serve as receptors to control the activities of the channels.Vertebrate ENaC proteins are similar to degenerins of Caenorhabditis elegans []: deg-1, del-1, mec-4, mec-10 and unc-8. These proteins can be mutated to cause neuronal degradation, and are also thought to form sodium channels.Structurally, the proteins that belong to this family consist of about 510 to 920 amino acid residues. They are made of an intracellular N terminusregion followed by a transmembrane domain, a large extracellular loop, a second transmembrane segment and a C-terminal intracellular tail [].For this entry the signature corresponds to the beginning of a conserved cysteine-rich region (there are nine conserved cysteines in a domain of about 65 residues), located at the C-terminal part of the extracellular loop.
Short Name	ENaC_CS