The pleckstrin homology domains of phospholipases C-β and -δ confer activation through a common site

Mammalian inositol-specific phospholipase C-beta(2) (PLCbeta(2)) and PLCdelta(1) differ in their cellular activators. PLCbeta(2) can be activated by Gbetagamma subunits, whereas PLCdelta(1) can be activated by phosphatidylinositol 4,5 bisphosphate (PI(4,5) P-2). For both proteins, the N-terminal pleckstrin homology (PH) domain appears to mediate activation. Here, we have constructed a chimera in which we placed the N-terminal PH domain of PLCdelta(1) into remaining C-terminal regions of PLCbeta(2). The PHdeltaPLCbeta chimera showed PI(4,5)P-2-dependent membrane binding similar to PLCdelta(1) and a Gbetagamma interaction energy close to that of PLCdelta(1). Like PLCdelta(1), the chimera was activated by PI( 4,5) P2 through the PH domain but not by Gbetagamma. Because these and previous results indicate a common site of contact between the PH and catalytic domains in these two enzymes, we computationally docked the known structures of the PH and catalytic domains of PLCdelta(1). A synthetic peptide whose sequence matches a potential interaction site between the two domains inhibited the basal activity of PLCbeta(2), PLCdelta(1), and a Gbetagamma-activable PHbeta(2)-PLCdelta(1) chimera. Also, the peptide was able to inhibit PI(4,5) P-2 and Gbetagamma activation of the PH-PLCdelta(1) PH-PLCbeta(2) enzymes in a concentration-dependent manner, suggesting that this is the region responsible for PH domain-mediated activation of the catalytic core.