Final answer:
The GTP binding pocket is a crucial part of G proteins for signal transduction, responsible for exchanging GDP for GTP to activate the protein and later hydrolyzing GTP to terminate the signal.
Step-by-step explanation:
The GTP binding pocket is an enzymatic region found in G proteins that is responsible for the hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP). G proteins are molecular switches that transmit signals from the outer cell environment to the cell's interior.
A good example of this process includes the interaction between hormones like glucagon and G-proteins resulting in the production of cAMP through the activation of adenylate cyclase. The G proteins are composed of three subunits: alpha, beta, and gamma. When a signaling molecule binds to a G-protein-coupled receptor, GDP is exchanged for GTP on the alpha subunit.
This activation leads to the dissociation of the beta and gamma subunits, triggering a cellular response. Eventually, the alpha subunit will hydrolyze the GTP back to GDP, becoming inactive, and reassociate with the beta and gamma subunits, hence terminating the signal. Crystallographic studies have shown the structure of these protein domains and the critical roles the amino acid residues play in the binding and hydrolysis of GTP.