Structural Determinants for Phosphatidic Acid Regulation of

Signaling fromGprotein-coupled receptors to phospholipase C- (PLC-) is regulated by coordinate interactions among multiple intracellular signaling molecules. Phosphatidic acid (PA), a signaling phospholipid, binds to and stimulates PLC-1 through a mechanism that requires the PLC-1 C-terminal domain. PA also modulates Gq stimulation of PLC-1. These data suggest that PA may have a key role in the regulation of PLC-1 signaling in cells. The present studies addressed the structural requirements and the mechanism for PA regulation of PLC-1. We used a combination of enzymatic assays, PA-binding assays, and circular dichroism spectroscopy to evaluate the interaction of PA with wild-type and mutant PLC-1 pro-teins andwith fragments of theGq bindingdomain.The results identify a region that includes the A helix and flexible loop of the Gq-binding domain as necessary for PA regulation.