Arginine residue 155 in the second intracellular loop plays a critical role in rat melanin-concentrating hormone receptor 1 activation.
Melanin-concentrating hormone (MCH) receptor 1 (MCH1R) is a class A G protein-coupled receptor. The MCH system has been linked to a variety of physiological functions, including the regulation of feeding and energy metabolism. We recently reported the importance of a dibasic motif in the membrane-proximal C-terminal region for MCH1R function. Here we reveal that an Arg residue in intracellular loop 2 of MCH1R plays a critical role in receptor function. We analyzed the roles of two distinct motifs, BBXXB and BXBB (in which B is a basic residue and X is a nonbasic residue), located in the three intracellular loops of MCH1R. Triple-substitution mutants of intracellular loops 1 and 3 could still activate calcium mobilization, albeit with lower efficacy or potency. However, mutations in intracellular loop 2 led to a complete loss of induction of signal transduction without changing the high affinity constant (Kd) value. By analyzing a series of single-substitution mutants, a point mutation of Arg155 in intracellular loop 2 was found to be responsible for the signaling pathway elicited by MCH. In addition, substitution at positions corresponding to Arg155 in human MCH receptor 2 and rat somatostatin receptor 2 also markedly abolished their ligand-induced signaling capacities, indicating that this Arg is a recognition determinant in several G protein-coupled receptors.
Saito
Yumiko
Y
Department of Pharmacology, Saitama Medical School, 38 Moro-Hongo, Moroyama-cho, Iruma-gun, Saitama 350-0492, Japan. yumisait@saitama-med.ac.jp
Tetsuka
Mitsue
M
Saito
Seiji
S
Imai
Kensaku
K
Yoshikawa
Ayumu
A
Doi
Hirofumi
H
Maruyama
Kei
K
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001120:Arginine; D020013:Calcium Signaling / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D005434:Flow Cytometry; D006801:Humans; D007028:Hypothalamic Hormones / Q000502:physiology; D008543:Melanins / Q000502:physiology; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010907:Pituitary Hormones / Q000502:physiology; D017433:Protein Structure, Secondary; D051381:Rats; D011979:Receptors, Pituitary Hormone / Q000737:chemistry / Q000235:genetics*; D017481:Receptors, Somatostatin / Q000737:chemistry / Q000235:genetics*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014162:Transfection
D007028:Hypothalamic Hormones; C491208:MCHR1 protein, rat; D008543:Melanins; D010907:Pituitary Hormones; D011979:Receptors, Pituitary Hormone; D017481:Receptors, Somatostatin; D011994:Recombinant Proteins; C115977:Sstr2 protein, rat; C092274:melanin-concentrating hormone receptor; C019463:melanin-concentrating hormone; D001120:Arginine