Rac Regulates Its Effector Phospholipase Cγ(2) through Interaction with a Split Pleckstrin Homology Domain

Several isoforms of phospholipase C (PLC) are regulated through interactions with Ras superfamily GTPases, including Rac proteins. Interestingly, of two closely related PLCγ isoforms, only PLCγ(2) has previously been shown to be activated by Rac. Here, we explore the molecular basis of this interaction as well as the structural properties of PLCγ(2) required for activation. Based on reconstitution experiments with isolated PLCγ variants and Rac2, we show that an unusual pleckstrin homology (PH) domain, designated as the split PH domain (spPH), is both necessary and sufficient to effect activation of PLCγ(2) by Rac2. We also demonstrate that Rac2 directly binds to PLCγ(2) as well as to the isolated spPH of this isoform. Furthermore, through the use of NMR spectroscopy and mutational analysis, we determine the structure of spPH, define the structural features of spPH required for Rac interaction, and identify critical amino acid residues at the interaction interface. We further discuss parallels and differences between PLCγ(1) and PLCγ(2) and the implications of our findings for their respective signaling roles.