Catalytic domain of metazoan phosphoinositide-specific phospholipase C-eta1
This subfamily corresponds to the catalytic domain present in metazoan phosphoinositide-specific phospholipase C (PI-PLC, EC 220.127.116.11)-eta isozyme 1. 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-eta represents a class of neuron-speific PI-PLC that has an N-terminal pleckstrin homology (PH) domain, an array of EF hands, a PLC catalytic core domain, a C2 domain, and a unique C-terminal tail that terminates with a PDZ-binding motif, a potential interaction site for other signaling proteins. The PLC catalytic core domain is a TIM barrel with two highly conserved regions (X and Y) split by a highly degenerate linker sequence. PI-PLC-eta1 is a neuron-specific enzyme and expressed in only nerve tissues such as the brain and spinal cord. It may perform a fundamental role in the brain.
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.