| Type: | Conserved_site | Name: | Peripherin/rom-1, conserved site |
| Description: | Tetraspanins are a distinct family of proteins, containing four transmembrane domains: a small outer loop (EC1), a larger outer loop (EC2), a small inner loop (IL) and short cytoplasmic tails. They contain characteristic structural features, including 4-6 conserved extracellular cysteine residues, and polar residues within transmembrane domains. A fundamental role of tetraspanins appears to be organizing other proteins into a network of multimolecular membrane microdomains, sometimes called the `tetraspanin web'. Within this web there are primary complexes in which tetraspanins show robust, specific, and direct lateral associations with other proteins. The strong tendency of tetraspanins to associate with each other probably contributes to the assembly of a network of secondary interactions in which non-tetraspanin proteins are associated with each other via palmitoylated tetraspanins acting as linker proteins. In addition, the association of lipids, such as gangliosides and cholesterol, probably contributes to the assembly of even larger tetraspanin complexes, which have some lipid raft-like properties (e.g. resistance to solubilization in non-ionic detergents). Within the tetraspanin web, tetraspanin proteins can associate not only with integrins and other transmembrane proteins, but also with signalling enzymes such as protein kinase C and phosphatidylinositol-4 kinase. Thus, the tetraspanin web provides a mechanistic framework by which membrane protein signalling can be expanded into a lateral dimension [].The outer segments of vertebrate rod photoreceptor cells are specialised organelles that function in the transduction of light into electrical signals as part of the visual excitation process. These organelles contain thousands of closely-stacked disk membranes, which have distinctly different protein compositions in their lamellar and rim regions []. Peripherin (or RDS) and rom-1 are related retinal-specific memebers of the tetraspanin family which are located at the rims of the photoreceptor disks, where they may act jointly in disk morphogenesis []. Both peripherin and rom-1 formdisulphide-linked homodimers. Defects in the peripherin gene (RDS) cause various human diseases such as autosomal dominant retinitis pigmentosa, autosomal dominant punctata albescens and butterfly-shaped pigment dystrophy. In mice it causes retinopathy known as 'retinal degeneration slow' (rds). These proteins contain about 350 amino acid residues. Structurally they consist of a short cytoplasmic N-terminal domain, followed by four transmembrane segments that delimit two lumenal and one cytoplasmic loops; the C-terminal domain is cytoplasmic. The second lumenal loop is very large (about 140 amino acid residues) and contains seven conserved cysteines. | Short Name: | Peripherin/rom-1_CS |
