Catalytic domain of metazoan phosphoinositide-specific phospholipase C-zeta
This family corresponds to the catalytic domain presenting in metazoan phosphoinositide-specific phospholipase C (PI-PLC, EC 3.1.4.11)-zeta isozyme. PI-PLC is a signaling enzyme that hydrolyzes the membrane phospholipids phosphatidylinositol-4,5-bisphosphate (PIP2) 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. Calcium is required for the catalysis. PI-PLC-zeta represents a class of sperm-specific PI-PLC that has an N-terminal EF-hand domain, a PLC catalytic core domain, and a C-terminal C2 domain. The PLC catalytic core domain is a TIM barrel with two highly conserved regions (X and Y) split by a highly degenerate linker sequence. There is one PLC-zeta isozyme (1). PLC-zeta plays a fundamental role in vertebrate fertilization by initiating intracellular calcium oscillations that trigger the embryo development. However, the mechanism of its activation still remains unclear. Aside from PI-PLC-zeta identified in mammals, its eukaryotic homologs have been classified with this family.
Comment:Both prokaryotic and eukaryotic PI-PLCs utilize a similar catalytic mechanism, a general base and acid catalysis involving two well conserved histidines. It consists of two steps, a phosphotransfer and a phosphodiesterase reaction.
Comment:Based on structure evidence of the catalytic site in Homo sapiens phospholipase C beta 2.
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