First cytoplasmic loop of glucagon-like peptide-1 receptor can function at the third cytoplasmic loop position of rhodopsin.
G protein-coupled receptors (GPCRs) are classified into several families based on their amino acid sequences. In family 1, GPCRs such as rhodopsin and adrenergic receptor, the structure-function relationship has been extensively investigated to demonstrate that exposure of the third cytoplasmic loop is essential for selective G protein activation. In contrast, much less is known about other families. Here we prepared chimeric mutants between Gt-coupled rhodopsin and Gi/Go- and Gs-coupled glucagon-like peptide-1 (GLP-1) receptor of family 2 and tried to identify the loop region that functions at the third cytoplasmic loop position of rhodopsin. We succeeded in expressing a mutant having the first cytoplasmic loop of GLP-1 receptor and found that this mutant activated Gi and Go efficiently but did not activate Gt. Moreover, the rhodopsin mutant having the first loop of Gs-coupled secretin receptor of family 2 decreased the Gi and Go activation efficiencies. Therefore, the first loop of GLP-1 receptor would share a similar role to the third loop of rhodopsin in G protein activation. This result strongly suggested that different families of GPCRs have maintained molecular architectures of their ancestral types to generate a common mechanism, namely exposure of the cytoplasmic loop, to activate peripheral G protein.
Yamashita
Takahiro
T
Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan.
Tose
Koji
K
Shichida
Yoshinori
Y
D000595:Amino Acid Sequence; D000818:Animals; D003593:Cytoplasm; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D003624:Darkness; D000067757:Glucagon-Like Peptide-1 Receptor; D000067758:Glucagon-Like Peptide-2 Receptor; D008027:Light; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D018027:Receptors, Glucagon / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism
D018076:DNA, Complementary; D000067757:Glucagon-Like Peptide-1 Receptor; D000067758:Glucagon-Like Peptide-2 Receptor; D010446:Peptide Fragments; D018027:Receptors, Glucagon; D012243:Rhodopsin