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X-ray Crystal Structures of Transforming p21 Ras Mutants Suggest a Transition-State Stabilization Mechanism for GTP Hydrolysis

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 thi...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1992-04, Vol.89 (8), p.3649-3653
Main Authors: Prive, Gilbert G., Milburn, Michael V., Tong, Liang, deVos, Abraham M., Yamaizumi, Ziro, Nishimura, Susumu, Kim, Sung-Hou
Format: Article
Language:English
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Summary: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 γ-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.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.89.8.3649