Catalytic domain of metazoan phosphoinositide-specific phospholipase C-etaThis family corresponds to the catalytic domain present in metazoan phosphoinositide-specific phospholipase C (PI-PLC, EC 188.8.131.52)-eta 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. 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. There are two PI-PLC-eta isozymes (1-2), both neuron-specific enzymes. They function as calcium sensors that are activated by small increases in intracellular calcium concentrations. The PI-PLC-eta isozymes are also activated through GPCR stimulation. Aside from the PI-PLC-eta isozymes identified in mammals, their eukaryotic homologs are also present in this family.