Catalytic domain of metazoan phosphoinositide-specific phospholipase C-gamma2
This subfamily corresponds to the catalytic domain present in metazoan phosphoinositide-specific phospholipase C (PI-PLC, EC 3.1.4.11)-gamma isozyme 2. PI-PLC is a signaling enzyme that hydrolyze 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 goes on to phosphorylate other molecules, leading to altered cellular activity. Calcium is required for the catalysis. PI-PLC-gamma 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 C2 domain. The PLC catalytic core domain is a TIM barrel with two highly conserved regions (X and Y) split by a highly degenerate linker sequence. Unique to PI-PLC-gamma2, a second PH domain, two SH2 (Src homology 2) regions, and one SH3 (Src homology 3) region is present within this linker region. PI-PLC-gamma2 is highly expressed in cells of hematopoietic origin. It is activated by receptor and non-receptor tyrosine kinases due to the presence of two SH2 and a single SH3 domain within the linker region. Unlike PI-PLC-gamma1, the activation of PI-PLC-gamma2 may require concurrent stimulation of PI 3-kinase.
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.
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