What vibrations tell us about GTPases.

In this review, we discuss how time-resolved Fourier transform infrared (FTIR) spectroscopy is used to understand how GTP hydrolysis is catalyzed by small GTPases and their cognate GTPase-activating proteins (GAPs). By interaction with small GTPases, GAPs regulate important signal transduction pathways and transport mechanisms in cells. The GTPase reaction terminates signaling and controls transport. Dysfunctions of GTP hydrolysis in these proteins are linked to serious diseases including cancer. Using FTIR, we resolved both the intrinsic and GAP-catalyzed GTPase reaction of the small GTPase Ras with high spatiotemporal resolution and atomic detail. This provided detailed insight into the order of events and how the active site is completed for catalysis. Comparisons of Ras with other small GTPases revealed conservation and variation in the catalytic mechanisms. The approach was extended to more nearly physiological conditions at a membrane. Interactions of membrane-anchored GTPases and their extraction from the membrane are studied using the attenuated total reflection (ATR) technique.