Catalytic domain of metazoan phosphoinositide-specific phospholipase C-epsilon
This family corresponds to the catalytic domain present in metazoan phosphoinositide-specific phospholipase C (PI-PLC, EC 220.127.116.11)-epsilon 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-epsilon represents a class of mammalian PI-PLC that has an N-terminal CDC25 homology domain with a guanyl-nucleotide exchange factor (GFF) activity, a pleckstrin homology (PH) domain, an array of EF hands, a PLC catalytic core domain, a C2 domain, and two predicted RA (Ras association) domains that are implicated in the binding of small GTPases, such as Ras or Rap, from the Ras family. 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 PI-PLC-epsilon isozyme (1). PI-PLC-epsilon is activated by G alpha(12/13), G beta gamma, and activated members of Ras and Rho small GTPases. Aside from PI-PLC-epsilon 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.