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

Abstract

Mammalian inositol-specific phospholipase C-β2 (PLCβ2) and PLCδ1, differ in their cellular activators. PLCβ2 can be activated by Gβγ subunits, whereas PLCδ1 can be activated by phosphatidylinositol 4,5 bisphosphate (PI(4,5)P2). 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 PLCδ1 into remaining C-terminal regions of PLCβ2. The PHδPLCβ chimera showed PI(4,5)P2-dependent membrane binding similar to PLCδ1 and a Gβγ interaction energy close to that of PLCδ1. Like PLCδ1, the chimera was activated by PI(4,5)P2 through the PH domain but not by Gβγ. 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 PLCδ1. A synthetic peptide whose sequence matches a potential interaction site between the two domains inhibited the basal activity of PLCβ2, PLCδ1, and a Gβγ-activable PHβ2-PLCδ1 chimera. Also, the peptide was able to inhibit PI(4,5)P2 and Gβγ activation of the PH-PLCδ1 PH-PLCβ2 enzymes in a concentration-dependent manner, suggesting that this is the region responsible for PH domain-mediated activation of the catalytic core.