User:Cboursnell/Sandbox/7TM GPCR Srz

G-protein-coupled receptors, GPCRs, constitute a vast protein family that encompasses a wide range of functions (including various autocrine, paracrine and endocrine processes). They show considerable diversity at the sequence level, on the basis of which they can be separated into distinct groups. We use the term clan to describe the GPCRs, as they embrace a group of families for which there are indications of evolutionary relationship, but between which there is no statistically significant similarity in sequence. The currently known clan members include the rhodopsin-like GPCRs, the secretin-like GPCRs, the cAMP receptors, the fungal mating pheromone receptors, and the metabotropic glutamate receptor family. There is a specialised database for GPCRs (http://www.gpcr.org/7tm/).

The nematode Caenorhabditis elegans has only 14 types of chemosensory neuron, yet is able to sense and respond to several hundred different chemicals because each neuron detects several stimuli. Chemoperception is one of the central senses of soil nematodes like C. elegans which are otherwise 'blind' and 'deaf'. Chemoreception in C. elegans is mediated by members of the seven-transmembrane G-protein-coupled receptor class (7TM GPCRs). More than 1300 potential chemoreceptor genes have been identified in C. elegans, which are generally prefixed sr for serpentine receptor. The receptor superfamilies include Sra (Sra, Srb, Srab, Sre), Str (Srh, Str, Sri, Srd, Srj, Srm, Srn) and Srg (Srx, Srt, Srg, Sru, Srv, Srxa), as well as the families Srw, Srz, Srbc, Srsx and Srr. Many of these proteins have homologues in Caenorhabditis briggsae.

This entry represents serpentine receptor class z (Srz), a solo family amongst the superfamilies of chemoreceptors. The genes encoding Srz appear to be under strong adaptive evolutionary pressure.