G-PROTEIN BETA-GAMMA-SUBUNITS

Guanine nucleotide binding (G) proteins relay extracellular signals en coded in light, small molecules, peptides, and proteins to activate or inhibit intracellular enzymes and ion channels. The larger G proteins , made up of G(alpha beta gamma) heterotrimers, dissociate into G(alph a) and G(beta gamma) subunits that separately activate intracellular e ffector molecules. Only recently has the G(beta gamma) subunit been re cognized as a signal transduction molecule in its own right; G(beta ga mma) is now known to directly regulate as many different protein targe ts as the G(alpha) subunit. Recent X-ray crystallography of G(alpha), G(beta gamma), and G(alpha beta gamma) subunits will guide the investi gation of structure-function relationships.