title: Involvement of specific hydrophobic, but not hydrophilic, amino acids in the third intracellular loop of the beta-adrenergic receptor in the activation of Gs.
abstract: Mutagenesis and biochemical analysis have indicated that amino acid residues at the amino terminus of the third intracellular loops of guanine nucleotide-binding protein (G protein)-coupled receptors are important in mediating the coupling of the receptors to G proteins. Because the primary sequence of this region is not conserved among all receptors that couple to the same G protein, it has been suggested that some other physicochemical property of this domain may determine G protein activation. To determine the relative contributions of charge distribution and amino acid side chain interactions within this domain of the beta-adrenergic receptor (beta AR) to the activation of the G protein Gs, point mutations were introduced into this region of the beta AR. Replacement of all four of the basic amino acid residues within this region (amino acids 222-236) with serine residues had a negligible effect on the ability of the beta AR to activate Gs. In contrast, replacement of the hydrophobic amino acids within this same region with leucine residues resulted in a mutant receptor that was poorly coupled to Gs. These results suggest that specific hydrophobic interactions within this region of the receptor may play a more significant role than ionic or hydrophilic interactions in mediating G protein activation.
authors.affiliation: Department of Molecular Pharmacology and Biochemistry, Merck Research Laboratories, Rahway, New Jersey 07065.
authors.forename: A H
authors.initials: AH
authors.lastname: Cheung
authors.forename: R R
authors.initials: RR
authors.lastname: Huang
authors.forename: C D
authors.initials: CD
authors.lastname: Strader
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000502:physiology*; D000818:Animals; D016466:CHO Cells / Q000502:physiology; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006224:Cricetinae; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D015870:Gene Expression / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D011943:Receptors, Adrenergic, beta / Q000235:genetics / Q000502:physiology*; D013329:Structure-Activity Relationship
chemical_list: D000596:Amino Acids; D011943:Receptors, Adrenergic, beta; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases