Catalytic domain of putative yeast phosphatidylinositide-specific phospholipases C
This family corresponds to the catalytic domain present in a group of putative phosphoinositide-specific phospholipase C (PI-PLC, EC 22.214.171.124) encoded by PLC1 genes from yeasts, which are homologs of the delta isoforms 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 prototype of this CD is protein Plc1p encoded by PLC1 genes from Saccharomyces cerevisiae. Plc1p contains both highly conserved X- and Y- regions of PLC catalytic core domain, as well as a presumptive EF-hand like calcium binding motif. Experiments show that Plc1p displays calcium dependent catalytic properties with high similarity to those of the mammalian PLCs, and plays multiple roles in modulating the membrane/protein interactions in filamentation control. CaPlc1p encoded by CAPLC1 from the closely related yeast Candida albicans, an orthologue of S. cerevisiae Plc1p, is also included in this group. Like Plc1p, CaPlc1p has conserved presumptive catalytic domain, shows PLC activity when expressed in E. coli, and is involved in multiple cellular processes. There are two other gene copies of CAPLC1 in C. albicans, CAPLC2 (also named as PIPLC) and CAPLC3. Experiments show CaPlc1p is the only enzyme in C. albicans which functions as PLC. The biological functions of CAPLC2 and CAPLC3 gene products must be clearly different from CaPlc1p, but their exact roles remain unclear. Moreover, CAPLC2 and CAPLC3 gene products are more similar to extracellular bacterial PI-PLC than to the eukaryotic PI-PLC, and they are not included in this subfamily.
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.