cd08558

Catalytic domain of eukaryotic phosphoinositide-specific phospholipase C and similar proteins; This family corresponds to the catalytic domain present in eukaryotic phosphoinositide-specific phospholipase C (PI-PLC, EC 3.1.4.11) and similar proteins. The higher eukaryotic PI-PLCs play a critical role in most signal transduction pathways, controlling numerous cellular events such as cell growth, proliferation, excitation and secretion. They strictly require Ca2+ for the catalytic activity. They display a clear preference towards the hydrolysis of the more highly phosphorylated membrane phospholipids PI-analogues, phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol-4-phosphate (PIP), to generate two important second messengers in eukaryotic signal transduction cascades, inositol 1,4,5-trisphosphate (InsP3) and diacylglycerol (DAG). InsP3 triggers inflow of calcium from intracellular stores, while DAG, together with calcium, activates protein kinase C, which then phosphorylates other molecules, leading to altered cellular activity. The eukaryotic PI-PLCs have a multidomain organization that consists of a PLC catalytic core domain, and various regulatory domains, such as the pleckstrin homology (PH) domain, EF-hand motif, and C2 domain. The catalytic core domain is a TIM barrel with two highly conserved regions (X and Y) split by a linker region. The catalytic mechanism of eukaryotic PI-PLCs is based on general base and acid catalysis utilizing two well conserved histidines and consists of two steps, a phosphotransfer and a phosphodiesterase reaction. The mammalian PI-PLCs consist of 13 isozymes, which are classified into six-subfamilies, PI-PLC-delta (1,3 and 4), -beta(1-4), -gamma(1,2), -epsilon, -zeta, and -eta (1,2). Ca2+ is required for the activation of all forms of mammalian PI-PLCs, and the concentration of calcium influences substrate specificity. This family also includes metazoan phospholipase C related but catalytically inactive proteins (PRIP), which belong to a group of novel inositol trisphosphate binding proteins. Due to the replacement of critical catalytic residues, PRIP does not have PLC enzymatic activity.