Catalytic domain of bacterial phosphatidylinositol-specific phospholipase C and similar proteins
This subfamily corresponds to the catalytic domain present in bacterial phosphatidylinositol-specific phospholipase C (PI-PLC, EC 4.6.1.13) and their sequence homologs found in eukaryota. Bacterial PI-PLCs participate in Ca2+-independent PI metabolism, hydrolyzing the membrane lipid phosphatidylinositol (PI) to produce phosphorylated myo-inositol and diacylglycerol (DAG). Although their precise physiological function remains unclear, bacterial PI-PLCs may function as virulence factors in some pathogenic bacteria. Bacterial PI-PLCs contain a single TIM-barrel type catalytic domain. Its catalytic mechanism is based on general base and acid catalysis utilizing two well conserved histidines, and consists of two steps, a phosphotransfer and a phosphodiesterase reaction. Eukaryotic homologs in this family are named as phosphatidylinositol-specific phospholipase C X domain containing proteins (PI-PLCXD). They are distinct from the typical eukaryotic phosphoinositide-specific phospholipases C (PI-PLC, EC 3.1.4.11), which have a multidomain organization that consists of a PLC catalytic core domain, and various regulatory domains. The catalytic core domain is assembled from two highly conserved X- and Y-regions split by a divergent linker sequence. In contrast, eukaryotic PI-PLCXDs contain a single TIM-barrel type catalytic domain, X domain, which is closely related to that of bacterial PI-PLCs. Although the biological function of eukaryotic PI-PLCXDs still remains unclear, it may be distinct from that of typical eukaryotic PI-PLCs. This family also includes a distinctly different type of eukaryotic PLC, glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC), an integral membrane protein characterized in the protozoan parasite Trypanosoma brucei. T. brucei GPI-PLC hydrolyzes the GPI-anchor on the variant specific glycoprotein (VSG), releasing dimyristyl glycerol (DMG), which may facilitate the evasion of the protozoan to the host's immune system. It does not require Ca2+ for its activity and is more closely related to bacterial PI-PLCs, but not mammalian PI-PLCs.
Comment:Both prokaryotic and eukaryotic phosphatidylinositol-specific phospholipase Cs 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.
Structure:1GYM; Bacillus cereus phosphatidylinositol-specific phospholipase C catalytic site
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