title: X-ray crystal structures of transforming p21 ras mutants suggest a transition-state stabilization mechanism for GTP hydrolysis.
abstract: RAS genes isolated from human tumors often have mutations at positions corresponding to amino acid 12 or 61 of the encoded protein (p21), while retroviral ras-encoded p21 contains substitutions at both positions 12 and 59. These mutant proteins are deficient in their GTP hydrolysis activity, and this loss of activity is linked to their transforming potential. The crystal structures of the mutant proteins are presented here as either GDP-bound or GTP-analogue-bound complexes. Based on these structures, a mechanism for the p21 GTPase reaction is proposed that is consistent with the observed structural and biochemical data. The central feature of this mechanism is a specific stabilization complex formed between the Gln-61 side-chain and the pentavalent gamma-phosphate of the GTP transition state. Amino acids other than glutamine at position 61 cannot stabilize the transition state, and amino acids larger than glycine at position 12 would interfere with the transition-state complex. Thr-59 disrupts the normal position of residue 61, thus preventing its participation in the transition-state complex.
authors.affiliation: Department of Chemistry, University of California, Berkeley 94720.
authors.forename: G G
authors.initials: GG
authors.lastname: Privé
authors.forename: M V
authors.initials: MV
authors.lastname: Milburn
authors.forename: L
authors.initials: L
authors.lastname: Tong
authors.forename: A M
authors.initials: AM
authors.lastname: de Vos
authors.forename: Z
authors.initials: Z
authors.lastname: Yamaizumi
authors.forename: S
authors.initials: S
authors.lastname: Nishimura
authors.forename: S H
authors.initials: SH
authors.lastname: Kim
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D016283:Proto-Oncogene Proteins p21(ras) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D006160:Guanosine Triphosphate; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)