Structural Insights into Phospholipase Cɛ Function

Abstract

Phospholipase C (PLC) is a member of the PLC family of enzymes, which hydrolyze phosphatidylinositol lipids following the activation of G protein coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs). PLC is unique among the PLC superfamily as it contains an Nterminal CDC25 domain, which has a guanine nucleotide exchange factor (GEF) activity for the small G protein Rap1A, and two C-terminal Ras association (RA) domains that bind scaffolding proteins and activated G proteins. PLC activity plays an important role in cardiomyocyte contractility and survival. The best-characterized pathway of PLC activation is mediated by adrenergic (-AR) receptors. Stimulation of these receptors culminates in the activation of the small GTPase Rap1A, which binds to PLC at the sarcoplasmic reticulum. There, PLC hydrolyzes phosphatidylinol-4-phosphate (PI4P) to produce diacylglycerol (DAG). Prolonged activation of this pathway results in increased Ca 2+ -induced Ca 2+ release (CICR) and increased expression of hypertrophy-related genes. However, the structural basis of PLC basal activity, and the mechanism of Rap1A activation are largely unknown. We have now obtained the first highresolution structure of PLC. These studies, together with biochemical validation of our structurebased hypotheses, provide the first molecular insights into this enzyme. 9 CHAPTER 1.