Catalytic domain of metazoan phosphoinositide-specific phospholipase C-delta1
This subfamily corresponds to the catalytic domain present in metazoan phosphoinositide-specific phospholipase C (PI-PLC, EC 3.1.4.11)-delta1 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 subfamily 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). PI-PLC-delta1 is relatively well characterized. It is activated by high calcium levels generated by other PI-PLC family members, and therefore functions as a calcium amplifier within the cell. Unlike PI-PLC-delta 4, PI-PLC-delta1 and 3 possess a putative nuclear export sequence (NES) located in the EF-hand domain, which may be responsible transporting PI-PLC-delta1and 3 from the cell nucleus. Experiments show PI-PLC-delta1 is essential for normal hair formation.
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.
Structure:1DJX; Rat Phosphoinositide-specific phospholipase C-Delta1 catalytic residues are well conserved in all eukaryotic PI-PLCs.