Detection of G protein-activator regions in M4 subtype muscarinic, cholinergic, and alpha 2-adrenergic receptors based upon characteristics in primary structure.
The 14-residue region Arg2410-Lys2423 of the human insulin-like growth factor II receptor possesses the ability to stimulate Gi, the activity being dependent on two structural characteristics: (i) at least two basic residues at the N-terminal side and (ii) the C-terminal motif, B-B-X-B or B-B-X-X-B (where B is a basic residue and X is a non-basic residue). The regions satisfying (i) and (ii) with 10 less than or equal to residue length less than or equal to 26 were located in all of the third inner loops and some of the other intracellular domains of the Gi-coupled M4 sub-type muscarinic cholinergic receptor (M4AChR) and the alpha 2-adrenergic receptor (alpha 2AR). Both the second inner loop 130-147 and the C-terminal portion of the third inner loop 382-400 (MIII) of human M4AChR had the ability to stimulate G proteins with the order Gi approximately Go greater than Gs, but only MIII could activate Gi/Go at nanomolar concentrations. In contrast, the N-terminal portion of the third inner loop 218-228 of human alpha 2AR-C10 activated Gi, Go, and Gs at micromolar concentrations with equal potency, whereas the further C-terminal portion of the third inner loop 301-313 of this receptor lacked the ability to activate any G protein. Among these active regions, only MIII indicated Mg(2+)-dependent Gi-stimulating function. Therefore, the search for the regions satisfying (i) and (ii) was useful to localize the G protein-activating activity of Gi-coupled receptors in limited regions, which were not always in the C-terminal portions of the third intracellular loops and activated G proteins in various modes of actions.
Okamoto
T
T
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
Nishimoto
I
I
D000595:Amino Acid Sequence; D000818:Animals; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D011942:Receptors, Adrenergic, alpha / Q000235:genetics / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000235:genetics / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000235:genetics / Q000378:metabolism*
D011942:Receptors, Adrenergic, alpha; D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins