Mutational and kinetic analyses of the GTPase-activating protein (GAP)-p21 interaction: the C-terminal domain of GAP is not sufficient for full activity. |
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| Authors: | P Gideon J John M Frech A Lautwein R Clark J E Scheffler and A Wittinghofer |
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| Affiliation: | Max-Planck-Institut für medizinische Forschung, Abteilung Biophysik, Heidelberg, Germany. |
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| Abstract: | The GTPase-activating protein (GAP) stimulates the GTPase reaction of p21 by 5 orders of magnitude such that the kcat of the reaction is increased to 19 s-1. Mutations of residues in loop L1 (Gly-12 and Gly-13), in loop L2 (Thr-35 and Asp-38), and in loop L4 (Gln-61 and Glu-63) influence the reaction in different ways, but all of these mutant p21 proteins still form complexes with GAP. The C-terminal domain of the human GAP gene product, GAP334, which comprises residues 714 to 1047, is 20 times less active than full-length GAP on a molar basis and has a fourfold lower affinity. This finding indicates that the N terminus of GAP containing the SH2 domains modifies the interaction between the catalytic domain and p21. |
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