Cell
Volume 96, Issue 6, 19 March 1999, Pages 893-902
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Article
Structural and Functional Analysis of the ARF1–ARFGAP Complex Reveals a Role for Coatomer in GTP Hydrolysis

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Abstract

The crystal structure of the complex of ARF1 GTPase bound to GDP and the catalytic domain of ARF GTPase–activating protein (ARFGAP) has been determined at 1.95 Å resolution. The ARFGAP molecule binds to switch 2 and helix α3 to orient ARF1 residues for catalysis, but it supplies neither arginine nor other amino acid side chains to the GTPase active site. In the complex, the effector-binding region appears to be unobstructed, suggesting that ARFGAP could stimulate GTP hydrolysis while ARF1 maintains an interaction with its effector, the coatomer complex of COPI-coated vesicles. Biochemical experiments show that coatomer directly participates in the GTPase reaction, accelerating GTP hydrolysis a further 1000-fold in an ARFGAP-dependent manner. Thus, a tripartite complex controls the GTP hydrolysis reaction triggering disassembly of COPI vesicle coats.

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