Catalytic domain of metazoan phosphoinositide-specific phospholipase C-delta4
This subfamily corresponds to the catalytic domain present in metazoan phosphoinositide-specific phospholipase C (PI-PLC, EC 184.108.40.206)-delta4 isozymes. 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. PLC-delta represents a class of mammalian PI-PLC that has an N-terminal pleckstrin homology (PH) domain, an array of EF hands, a PLC catalytic core domain, and a C-terminal C2 domain. This CD corresponds to the catalytic domain which is a TIM barrel with two highly conserved regions (X and Y) split by a highly degenerate linker sequence. There are three PI-PLC-delta isozymes (1,3 and 4). Unlike PI-PLC-delta 1 and 3, a putative nuclear export sequence (NES) located in the EF-hand domain, which may be responsible transporting PI-PLC-delta1 and 3 from the cell nucleus, is not present in PI-PLC-delta4. Experiments show PI-PLC-delta4 is required for the acrosome reaction in fertilization.
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 the structure evidence of the catalytic site in Rat Phosphoinositide-specific phospholipase C-Delta1.