title: Quantitative analysis of mutually competitive binding of human Raf-1 and yeast adenylyl cyclase to Ras proteins.
abstract: Ras proteins appear to have two distinct downstream effectors, adenylyl cyclase in Saccharomyces cerevisiae and a product of raf-1 protooncogene in higher organisms. We found that in vitro activation of adenylyl cyclase by yeast Ras2 and human H-Ras proteins is subject to competitive inhibition by its leucine-rich repeats domain and by the N-terminal regulatory domain of human Raf-1 protein. Kinetic analyses of the inhibition patterns enabled us to determine exact dissociation constants (Kd) of the two polypeptides for Ras2 and H-Ras. The leucine-rich repeats domain bound to the posttranslationally modified Ras2 with the Kd of approximately 13 nM, which was close to the value (7 nM) of the whole adenylyl cyclase. The Kd of Raf-1 for the modified H-Ras, 3.5 nM, was significantly lower than that for Ras2, 24 nM, whereas adenylyl cyclase bound preferentially to Ras2. Similar inhibition was also observed in vivo by suppression of RAS2Val-19-dependent heat shock sensitivity and of Ras-dependent cAMP response to glucose upon overexpression of Raf-1 in yeast. These results indicate that the leucine-rich repeats domain contains the Ras protein-binding site and that Raf-1 and adenylyl cyclase, sharing no structural homology with each other, bind to a similar, if not identical, region of Ras with comparable affinities.
authors.affiliation: Department of Physiology II, Kobe University School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Minato
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: K
authors.initials: K
authors.lastname: Akasaka
authors.forename: T
authors.initials: T
authors.lastname: Okada
authors.forename: N
authors.initials: N
authors.lastname: Suzuki
authors.forename: T
authors.initials: T
authors.lastname: Kataoka
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D000242:Cyclic AMP / Q000378:metabolism; D017931:DNA Primers; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins; D018631:ras Proteins
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D017931:DNA Primers; D005656:Fungal Proteins; D011518:Proto-Oncogene Proteins; D029701:Saccharomyces cerevisiae Proteins; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras); C489015:RAS2 protein, S cerevisiae; D018631:ras Proteins; D000262:Adenylyl Cyclases; D007930:Leucine; D005947:Glucose