title: Sites of interaction in the complex between beta- and gamma-subunits of transducin.
abstract: Transducin, the guanine nucleotide-binding regulatory protein in rod outer segments, is a heterotrimer consisting of alpha-, beta-, and gamma-subunits. Activation of the photoreceptor, rhodopsin, by light, results in activation of transducin which cleaves to form transducin alpha. GTP and a complex of beta gamma-subunits. We have investigated the point(s) of contact between the subunits of transducin by analyzing for the formation of intersubunit disulfide bond(s) in the presence of copper phenanthroline. The formation of a new species with an apparent molecular mass of 43 kDa was observed which had resulted from the formation of a disulfide bond between the beta- and gamma-subunits. The amino acid residues participating in the disulfide bond were identified as Cys-25 in the beta-subunit and Cys-36 and/or Cys-37 in the gamma-subunit. Thus, these cysteine residues and, probably, some of the adjacent amino acid residues form a point of contact between the beta- and gamma-subunits of transducin in the stable complex.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
authors.forename: J
authors.initials: J
authors.lastname: Bubis
authors.forename: H G
authors.initials: HG
authors.lastname: Khorana
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002850:Chromatography, Gel; D003300:Copper / Q000494:pharmacology; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004220:Disulfides / Q000378:metabolism; D004492:Edetic Acid; D005033:Ethylmaleimide / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010618:Phenanthrolines / Q000494:pharmacology; D011485:Protein Binding; D012374:Rod Cell Outer Segment / Q000378:metabolism; D015293:Transducin / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D003432:Cross-Linking Reagents; D004220:Disulfides; D046911:Macromolecular Substances; D010618:Phenanthrolines; D003300:Copper; D004492:Edetic Acid; D015293:Transducin; D005033:Ethylmaleimide; C025205:1,10-phenanthroline