orphan adhesion receptors GPR111 and GPR115, member of the class B2 family of seven-transmembrane G protein-coupled receptors
GPR111 and GPR115 are highly homologous orphan receptors that belong to group VI adhesion-GPCRs along with GPR110, GPR113, and GPR116. The adhesion receptors are characterized by the presence of large N-terminal extracellular domains containing multiple adhesion motifs, which play critical roles in ligand recognition as well as cell-cell adhesion and cell-matrix interactions, linked by a stalk region to a class B seven-transmembrane domain. In addition, almost all adhesion receptors, except GPR123, contain an evolutionarily conserved GPCR-autoproteolysis inducing (GAIN) domain that undergoes autoproteolytic processing at the GPCR proteolysis site (GPS) motif located immediately N-terminal to the first transmembrane region, to generate N- and C-terminal fragments (NTF and CTF), which may serve important biological functions. However, several adhesion GPCRs, including GPR 111, GPR115, and CELSR1, are predicted to be non-cleavable at the GAIN domain because of the lack of a consensus catalytic triad sequence (His-Leu-Ser/Thr) within their GPS. Both GPR111 and GPR5 are present only in land-living animals and are predominantly expressed in the developing skin.