Figure 1. Structure and Biochemistry of Wild-type RAC1, the Constitutively Active RAC1^Q61L mutant, and the Fast Cycling RAC1^P29S Mutant.

Comparison of crystal structures of RAC1^WT (light blue, PDB 3TH5) with RAC1^Q61L (light purple, PDB 4GZL), and RAC1^P29S (dark pink, PDB 3SBE) in complex with the slow hydrolyzing GTP analog GMPPNP (green). RAC1^P29S possesses a more flexible switch I domain than RAC^WT and RAC1^Q61L. The proline to serine substitution enables hydrogen bonding between Ser-29 and Gly-30 of switch I and GTP and constitutes the difference between fast cycling mutations such as P29S and GTP-hydrolysis deficient mutations such as Q61L. Residue 29 and surrounding residues are displayed in orange stick format to illustrate hydrogen bonding (red).