Catalytic domain of plant phosphatidylinositide-specific phospholipases C
This family corresponds to the catalytic domain present in a group of phosphoinositide-specific phospholipases C (PI-PLC, EC 188.8.131.52) encoded by PLC genes from higher plants, which are homologs of mammalian PI-PLC in terms of overall sequence similarity and domain organization. Mammalian 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. The domain arrangement of plant PI-PLCs is structurally similar to the mammalian PLC-zeta isoform, which lacks the N-terminal pleckstrin homology (PH) domain, but contains EF-hand like motifs (which are absent in a few plant PLCs), a PLC catalytic core domain with X- and Y- highly conserved regions split by a linker sequence, and a C2 domain. However, at the sequence level, the plant PI-PLCs are closely related to the mammalian PLC-delta isoform. Experiments show that plant PLCs display calcium dependent PLC catalytic properties, although they lack some of the N-terminal motifs found in their mammalian counterparts. A putative calcium binding site may be located at the region spanning the X- and Y- domains.
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.