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Updated: Jul 28, 2026

Comparing the Affinity of GTPase-binding Proteins using Competition Assays
Published on: October 8, 2015
Separate GTP binding and GTPase activating domains of a G alpha subunit
D W Markby1, R Onrust, H R Bourne
1Department of Pharmcology, University of California, San Francisco 94143.
Abstract:
Most members of the guanosine triphosphatase (GTPase) superfamily hydrolyze guanosine triphosphate (GTP) quite slowly unless stimulated by a GTPase activating protein or GAP. The alpha subunits (G alpha) of the heterotrimeric G proteins hydrolyze GTP much more rapidly and contain an approximately 120-residue insert not found in other GTPases. Interactions between a G alpha insert domain and a G alpha GTP-binding core domain, both expressed as recombinant proteins, show that the insert acts biochemically as a GAP. The results suggest a general mechanism for GAP-dependent hydrolysis of GTP by other GTPases.
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