Fluorescence Methods in the Study of Small GTP-Binding Proteins

A great variety of small guanosine triphosphate (GTP)-binding proteins are known, and each of these in turn interacts with a variety of regulatory proteins, including guanine-nucleotide dissociation inhibitors (GDIs), GTPase-activating proteins (GAPs) and guaninine nucleotide exchange factors (GEFs). Most importantly, the small GTPases bind to target “effector” proteins, and many of these have yet to be identified. This process generates a network of protein-nucleotide and protein-protein interactions, which underlies the biology of the corresponding transport or signal transduction process. Many of the interactions defined by two-hybrid analysis, blot overlay or glutathione-S-transferase (GST)-pulldown experiments require a more detailed analysis of their kinetics and thermodynamic properties in order to quantify these processes in vivo. It therefore becomes increasingly important to examine these interactions by appropriate real-time methods.