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Ras-related GTP-binding proteins function as molecular switches which cycle between GTP-bound 'on'- and GDP-bound 'off'-states. GTP hydrolysis is the common timing mechanism that mediates the return from the 'on' to the 'off'-state. It is usually slow but can be accelerated by orders of magnitude upon interaction with GTPase-activating proteins (GAPs). In the case of Ras, a major regulator of cellular growth, point mutations are found in approximately 30% of human tumours which render the protein unable to hydrolyse GTP, even in the presence of Ras-GAPs. The first structure determination of a GTPase-activating protein reveals the catalytically active fragment of the Ras-specific p120GAP (ref. 2), GAP-334, as an elongated, exclusively helical protein which appears to represent a novel protein fold. The molecule consists of two domains, one of which contains all the residues conserved among different GAPs for Ras. From the location of conserved residues around a shallow groove in the central domain we can identify the site of interaction with Ras x GTP. This leads to a model for the interaction between Ras and GAP that satisfies numerous biochemical and genetic data on this important regulatory process.

Crystal structure of the GTPase-activating domain of human p120GAP and implications for the interaction with Ras., Scheffzek K, Lautwein A, Kabsch W, Ahmadian MR, Wittinghofer A, Nature. 1996 Dec 12;384(6609):591-6. PMID:8955277

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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Categories: Homo sapiens | Ahmadian, M R. | Kabsch, W. | Lautwein, A. | Scheffzek, K. | Wittinghofer, A. | Cancer | Gap | Growth regulation | Gtpase activation | Ra | Signal transduction