Abstract

Phospholipase C (PLC) β2, a well studied member of the family of enzymes that catalyze the hydrolysis of the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP₂) into secondary messengers, can be activated by the Gβγ subunits of heterotrimeric G-proteins in a manner that depends on the presence and composition of the associated phospholipid membrane surface. The N-terminal pleckstrin homology (PH) domain of PLCβ2 mediates both the response to Gβγ and membrane binding, but how these interactions are coupled to yield an activated catalytic core remains unknown. Here we propose a mechanism based on molecular models of truncated PLCβ2 in its activated form complexed with Gβγ and in the catalytically inactive/membrane-bound form, obtained with the application of protein-protein docking algorithms and coarse-grained molecular dynamics simulations. These models were probed experimentally, and the inferences were confirmed by results from a combination of molecular biology and fluorescence assays. Results from the dynamic simulations of the molecular models and their interactions with various lipid bilayers identify the determinants of PLCβ2-PH domain specificity for Gβγ and lipid membranes and suggest a mechanism for the previously reported dependence of Gβγ activation on the associated membrane composition. Together, these findings explain the roles of the different activators in terms of their effect on the orientations of the PH and catalytic core domains relative to the lipid membranes.