Structure of the complex of Cdc42Hs with a peptide derived from p-21 activated kinase

Cdc42Hs is a member of the Ras superfamily of GTPases and initiates a casca de that begins with the activation of several kinases, including p21-activa ted kinase (PAK). We have previously used a 46 amino acid fragment of PAK ( PBD46) to define the binding surface on Cdc42Hs [Guo et al. (1998) Biochemi stry 37, 14030-14037], Here we describe the three-dimensional solution stru cture of the Cdc42Hs.GMPPCP-PBD46 complex. Heteronuclear NMR methods were u sed to assign resonances in the complex, and approximately 2400 distance an d dihedral restraints were used to calculate a set of 20 structures using a combination of distance geometry, simulated annealing, and chemical shift and Ramachandran refinement. The overall structure of Cdc42Hs in the comple x differs from the uncomplexed structure in two major aspects: (1) the firs t alpha helix is reoriented to accommodate the binding of the peptide and ( 2) the regions corresponding to switch I and switch II are less disordered. As suggested by our previous work (Guo et al., 1998) and similar to the co mplex between Cdc42Hs and fACK [Mott et al. (1999) Nature 399, 384-388], PB D46 forms an intermolecular beta-sheet with beta 2 of Cdc42Hs and contacts both switch I and switch II. The extensive binding surface between PBD46 an d Cdc42Hs can account for both the high affinity of the complex and the inh ibition by PBD46 of GTP hydrolysis.