Identification of a receptor/G-protein contact site critical for signaling specificity and G-protein activation.
Each G protein-coupled receptor recognizes only a distinct subset of the many structurally closely related G proteins expressed within a cell. How this selectively is achieved at a molecular level is not well understood, particularly since no specific point-to-point contact sites between a receptor and its cognate G protein(s) have been identified. In this study, we demonstrate that a 4-aa epitope on the m2 muscarinic acetylcholine receptor, a prototypical Gi/o-coupled receptor, can specifically recognize the C-terminal 5 aa of alpha subunits of the Gi/o protein family. The m2 receptor residues involved in this interaction are predicted to be located on one side of an alpha-helical receptor region present at the junction between the third intracellular loop and the sixth transmembrane domain. Coexpression studies with hybrid m2/m3 muscarinic receptors and mutant G-protein alpha q subunits showed that the receptor/G-protein contact site identified in this study is essential for coupling specificity and G-protein activation.
Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Dieseases, Bethesda, MD 20892, USA.
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J
Liu
B R
BR
Conklin
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N
Blin
J
J
Yun
J
J
Wess
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006868:Hydrolysis; D008969:Molecular Sequence Data; D010716:Phosphatidylinositols / Q000378:metabolism; D011485:Protein Binding; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D010738:Type C Phospholipases / Q000378:metabolism
D010716:Phosphatidylinositols; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D011993:Recombinant Fusion Proteins; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases