Discrete amino acid sequences of the alpha 1-adrenergic receptor determine the selectivity of coupling to phosphatidylinositol hydrolysis.
We have constructed a variety of chimeric beta 2/alpha 1 adrenergic receptors (AR) in which selected portions of the third intracellular loop of the alpha (1B)AR were substituted into the corresponding regions of the beta 2AR. The mutant receptors were both transiently and permanently expressed in COS-7 or L-cells, respectively, and tested for their ability to mediate epinephrine-induced activation of polyphosphoinositide (PI) hydrolysis and adenylylcyclase. We have determined that 27 amino acids of the alpha (1B)AR (residues 233-259) derived from the N-terminal portion of the third intracellular loop represent the structural determinant conferring to the beta 2AR the ability to activate PI hydrolysis. This finding suggests that in the alpha (1B)AR the N-terminal portion of the third intracellular loop plays a major role in determining the selectivity of receptor-G protein coupling. However, replacement of alpha 1B sequences in the third intracellular loop of the beta 2AR did not abolish the latter receptor's coupling to activation of adenylylcyclase, thus resulting in chimeric adrenergic receptors which activated both PI hydrolysis and adenylylcyclase. These results indicate that, even if the N-terminal portion of the third intracellular loop is a major determinant of the selectivity of receptor-G protein coupling, other structural domains of the receptors also modulate this property. The comparison of the amino acid sequences which determine the selectivity of G protein coupling in functionally similar receptors may help to elucidate the structural basis for activation of specific G protein-effector systems.
Cotecchia
S
S
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710.
Ostrowski
J
J
Kjelsberg
M A
MA
Caron
M G
MG
Lefkowitz
R J
RJ
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002678:Chimera; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D007739:L Cells; D051379:Mice; D008961:Models, Structural; D008969:Molecular Sequence Data; D010716:Phosphatidylinositols / Q000378:metabolism*; D016133:Polymerase Chain Reaction / Q000379:methods; D011942:Receptors, Adrenergic, alpha / Q000235:genetics / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013937:Thymidine Kinase / Q000172:deficiency / Q000235:genetics; D014162:Transfection
D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D011993:Recombinant Fusion Proteins; D004247:DNA; D013937:Thymidine Kinase; D000262:Adenylyl Cyclases; D004837:Epinephrine