title: Purification of a Ras-dependent mitogen-activated protein kinase kinase kinase from bovine brain cytosol and its identification as a complex of B-Raf and 14-3-3 proteins.
abstract: We previously purified a protein factor, named REKS (Ras-dependent Extracellular Signal-regulated Kinase (ERK)/mitogen-activated protein kinase Kinase (MEK) Stimulator), from Xenopus eggs by use of a cell-free assay system in which recombinant GTP gamma S (guanosine 5'-(3-O-thio)triphosphate)-Ki-Ras activates recombinant MEK. By use of this assay system, we purified here bovine REKS to near homogeneity from the cytosol fraction of bovine brain by successive chromatographies of Mono S, Mono Q, GTP gamma S-glutathione S-transferase-Ha-Ras-coupled glutathione-agarose, and Mono Q columns. It was composed of three proteins with masses of about 95, 32, and 30 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The 95-, 32-, and 30-kDa proteins were identified by immunoblot analysis to be B-Raf protein kinase, 14-3-3 protein, and 14-3-3 protein, respectively. Moreover, the REKS activity was specifically immunoprecipitated by an anti-B-Raf antibody. Bovine REKS was activated by lipid-modified GTP gamma S-Ki-Ras far more effectively than by a lipid-unmodified one. Lipid-modified GDP-Ki-Ras was inactive. Exogenous addition of 14-3-3 proteins stimulated further the REKS activity both in the presence and absence of GTP gamma S-Ki-Ras. These results indicate that at least one of the direct targets of Ras is B-Raf complexed with 14-3-3 proteins in bovine brain.
authors.affiliation: Department of Molecular Biology, Osaka University Medical School, Suita, Japan.
authors.forename: B
authors.initials: B
authors.lastname: Yamamori
authors.forename: S
authors.initials: S
authors.lastname: Kuroda
authors.forename: K
authors.initials: K
authors.lastname: Shimizu
authors.forename: K
authors.initials: K
authors.lastname: Fukui
authors.forename: T
authors.initials: T
authors.lastname: Ohtsuka
authors.forename: Y
authors.initials: Y
authors.lastname: Takai
mesh_terms: D048948:14-3-3 Proteins; D000818:Animals; D001921:Brain / Q000201:enzymology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry / Q000302:isolation & purification*; D002417:Cattle; D002474:Cell-Free System; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases; D019950:Mitogen-Activated Protein Kinase 1; D008970:Molecular Weight; D017346:Protein Serine-Threonine Kinases / Q000302:isolation & purification* / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000302:isolation & purification*; D011518:Proto-Oncogene Proteins / Q000302:isolation & purification* / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase
chemical_list: D048948:14-3-3 Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D014446:Tyrosine 3-Monooxygenase; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D019950:Mitogen-Activated Protein Kinase 1; D020930:MAP Kinase Kinase Kinases; C089319:Ras-dependent mitogen-activated protein kinase kinase kinase; D016283:Proto-Oncogene Proteins p21(ras)