A Novel Glucagon-Related Peptide (GCRP) and Its Receptor GCRPR Account for Coevolution of Their Family Members in Vertebrates

<div><p>The glucagon (GCG) peptide family consists of GCG, glucagon-like peptide 1 (GLP1), and GLP2, which are derived from a common GCG precursor, and the glucose-dependent insulinotropic polypeptide (GIP). These peptides interact with cognate receptors, GCGR, GLP1R, GLP2R, and GIPR, which belong to the secretin-like G protein-coupled receptor (GPCR) family. We used bioinformatics to identify genes encoding a novel GCG-related peptide (GCRP) and its cognate receptor, GCRPR. The <i>GCRP</i> and <i>GCRPR</i> genes were found in representative tetrapod taxa such as anole lizard, chicken, and <i>Xenopus</i>, and in teleosts including medaka, fugu, tetraodon, and stickleback. However, they were not present in mammals and zebrafish. Phylogenetic and genome synteny analyses showed that <i>GCRP</i> emerged through two rounds of whole genome duplication (2R) during early vertebrate evolution. <i>GCRPR</i> appears to have arisen by local tandem gene duplications from a common ancestor of <i>GCRPR</i>, <i>GCGR</i>, and <i>GLP2R</i> after 2R. Biochemical ligand-receptor interaction analyses revealed that GCRP had the highest affinity for GCRPR in comparison to other GCGR family members. Stimulation of chicken, <i>Xenopus</i>, and medaka GCRPRs activated Gα_s-mediated signaling. In contrast to chicken and <i>Xenopus</i> GCRPRs, medaka GCRPR also induced Gα_q/11-mediated signaling. Chimeric peptides and receptors showed that the K¹⁶M¹⁷K¹⁸ and G¹⁶Q¹⁷A¹⁸ motifs in GCRP and GLP1, respectively, may at least in part contribute to specific recognition of their cognate receptors through interaction with the receptor core domain. In conclusion, we present novel data demonstrating that <i>GCRP</i> and <i>GCRPR</i> evolved through gene/genome duplications followed by specific modifications that conferred selective recognition to this ligand-receptor pair.</p>