Editing G protein-coupled receptor (section)

==Origin and diversification of the superfamily==
[[Signal transduction]] mediated by the superfamily of GPCRs dates back to the origin of [[Multicellular organism|multicellularity]]. Mammalian-like GPCRs are found in [[fungi]], and have been classified according to the [[GRAFS]] classification system based on GPCR fingerprints.<ref name=pmid22238661>{{cite journal | vauthors = Krishnan A, Almén MS, Fredriksson R, Schiöth HB | title = The origin of GPCRs: identification of mammalian like Rhodopsin, Adhesion, Glutamate and Frizzled GPCRs in fungi | journal = PLOS ONE | volume = 7 | issue = 1 | pages = e29817 | year = 2012 | pmid = 22238661 | pmc = 3251606 | doi = 10.1371/journal.pone.0029817 | bibcode = 2012PLoSO...729817K | veditors = Xue C | doi-access = free }}</ref> Identification of the superfamily members across the [[eukaryotic]] domain, and comparison of the family-specific motifs, have shown that the superfamily of GPCRs have a common origin.<ref name=pmid21402729>{{cite journal | vauthors = Nordström KJ, Sällman Almén M, Edstam MM, Fredriksson R, Schiöth HB | title = Independent HHsearch, Needleman--Wunsch-based, and motif analyses reveal the overall hierarchy for most of the G protein-coupled receptor families | journal = Molecular Biology and Evolution | volume = 28 | issue = 9 | pages = 2471–80 | date = September 2011 | pmid = 21402729 | doi = 10.1093/molbev/msr061 | doi-access =  }}</ref> Characteristic motifs indicate that three of the five GRAFS families, ''[[Rhodopsin-like receptors|Rhodopsin]]'', [[adhesion G protein-coupled receptor|''Adhesion'']], and ''[[Frizzled]]'', evolved from the ''[[Dictyostelium]] discoideum'' cAMP receptors before the split of [[opisthokont]]s. Later, the ''[[Secretin receptor family|Secretin]]'' family evolved from the ''Adhesion'' GPCR receptor family before the split of [[nematode]]s.<ref name=pmid22238661/> Insect GPCRs appear to be in their own group and Taste2 is identified as descending from ''Rhodopsin''.<ref name=pmid21402729/> Note that the ''Secretin''/''Adhesion'' split is based on presumed function rather than signature, as the classical Class B (7tm_2, {{Pfam|PF00002}}) is used to identify both in the studies.