Gβγ Activates PIP2 Hydrolysis by Recruiting and Orienting PLCβ on the Membrane Surface

Abstract

PLC{beta}s catalyze the hydrolysis of PIP2 into IP3 and DAG. PIP2 regulates the activity of many membrane proteins, while IP3 and DAG lead to increased intracellular Ca2+ levels and activate PKC, respectively. PLC{beta}s are regulated by GPCRs through direct interaction with Gq and G{beta}{gamma}. This study addresses the mechanism by which G{beta}{gamma} activates PLC{beta}3. We show that PLC{beta}3 functions as a slow Michaelis-Menten enzyme (kcat~2 sec-1, KM~0.43 mol%) on membrane surfaces. Its partition coefficient (Kx~2.9 * 104) is such that only a small quantity of PLC{beta}3 exists in the membrane in the absence of G{beta}{gamma}. When G{beta}{gamma} is present, equilibrium binding (Keq~0.009 mol%) increases PLC{beta}3 in the membrane, increasing Vmax in proportion. Atomic structures on membrane vesicle surfaces show that two G{beta}{gamma} anchor PLC{beta}3 with its catalytic site oriented toward the membrane surface. This principle of activation explains rapid stimulated catalysis with low background catalysis.