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Abstract

Ras-GTPase-activating proteins (Ras-GAPs) are important regulators of the biological activity of Ras within the framework of intracellular communication where GTP-bound Ras (Ras:GTP) is a key signal transducing molecule (Trahey and McCormick, Science 238:542–545, 1987; Boguski and McCormick, Nature 366:643–654, 1993). By accelerating Ras-mediated GTP hydrolysis, Ras-GAPs provide an efficient means to reset the Ras- GTPase cycle to the GDP-bound ‘OFF’-state and terminate the Ras-mediated signal. Here we report the crystallization of the GTPaseactivating domain of the human p120GAP. The crystals belong to the orthorhombic space group symmetry P212121 with unit cell dimensions of a 5 42.2 Å, b 5 55.6 Å, c 5 142.2 Å, a 5 b 5 g 5 90°. Assuming a Matthews parameter of 2.2 Å3/Da, there is one molecule per asymmetric unit. Applying micro-seeding techniques, we grew large single crystals that could not be obtained by other routine methods for crystal improvement. They diffracted to a resolution of approximately 3 Å using X-rays from a rotating anode generator and to better than 1.8 Å in a synchrotron beam. Chemical cross-linking led to reduction of the maximum resolution but to significantly increased stability against mechanical and heavy atom stress