Mutation of a single TMVI residue, Phe(282), in the beta(2)-adrenergic receptor results in structurally distinct activated receptor conformations.
We showed previously that Phe(303) in transmembrane segment (TM) VI of the alpha(1B)-adrenergic receptor (alpha(1B)-AR), a residue conserved in many G protein-coupled receptors (GPCRs), is critically involved in coupling agonist binding with TM helical movement and G protein activation. Here the equivalent residue, Phe(282), in the beta(2)-AR was evaluated by mutation to glycine, asparagine, alanine, or leucine. Except for F282N, which exhibits attenuated basal and maximal isoproterenol stimulation, the Phe(282) mutants display varying degrees of constitutive activity (F282L > F282A > F282G), and as shown by the results of substituted cysteine accessibility method (SCAM) studies, induce movement of endogenous cysteine(s) into the water-accessible ligand-binding pocket. For F282A, movement is confined to Cys(285) in TMVI, whereas F282L induces movement of both Cys(285) in TMVI and Cys(327) in TMVII. Further, engineered cysteine-sensor studies indicate that F282L causes movement of TMVI, both above and below an apparent kink-inducing TMVI proline (Pro(288)), whereas that due to F282A is confined to the domain below Pro(288). A plausible interpretation of these data is that receptor activation involves rigid body movement of TMVI which, because of its Pro(288)-induced kink, acts as a pivot to transduce and amplify the agonist-induced conformational change in the upper domain, to a change in the lower domain required for productive receptor-G protein coupling.
Chen
Songhai
S
Molecular Cardiology and Biocomputing Units, Victor Chang Cardiac Research Institute, St. Vincent's Hospital, Darlinghurst, NSW 2010, Australia. songhai.chen@mcmail.vanderbilt.edu
Lin
Fang
F
Xu
Ming
M
Riek
R Peter
RP
Novotny
Jiri
J
Graham
Robert M
RM
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D019556:COS Cells; D003198:Computer Simulation; D017124:Conserved Sequence; D006224:Cricetinae; D019204:GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010649:Phenylalanine / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D008024:Ligands; D018343:Receptors, Adrenergic, beta-2; D011994:Recombinant Proteins; D010649:Phenylalanine; D019204:GTP-Binding Proteins