The fourth intracellular domain of G-protein coupling receptors: helicity, basicity and similarity to opsins.
The minimal size of the fourth intracellular domain of heptahelical G-protein coupling receptors (GPCRs) is close to 15 residues, and a juxtamembrane 15-residue segment is predicted as helical (Helix-8) in most of the receptors. Sequences of opsins, non-visual opsin-like (family A) GPCRs and Taste-2 receptors correspond with bovine rhodopsin at four positions in this tract. This is especially evident in monoamine receptors. In most GPCRs, the conserved juxtamembrane segment also has a large fraction of basic sidechains, and a considerable excess of cationic over anionic residues. The conservation is not dependent on the preferred G-protein alpha subunit or the overall length of the domain, indicating an additive speciation. In rod opsins and some A-GPCRs this segment has been shown to associate with the bilayer and to interact with G-proteins. The segment could also be involved in precoupling of receptors and transducers. These interactions could be helped by both the structural propensities and the high content of cationic sidechains.
Parker
Michael S
MS
Department of Molecular Cell Sciences, University of Memphis, Memphis, TN 38152, USA.
Parker
Steven L
SL
D000818:Animals; D002417:Cattle; D006801:Humans; D008969:Molecular Sequence Data; D055355:Opsins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D055355:Opsins; D043562:Receptors, G-Protein-Coupled