Catalytic domain of Streptomyces antibioticus phosphatidylinositol-specific phospholipase C1-like proteins
This subfamily corresponds to the catalytic domain present in Streptomyces antibioticus phosphatidylinositol-specific phospholipase C1 (SaPLC1) and similar proteins. The typical bacterial phosphatidylinositol-specific phospholipase C (PI-PLC, EC 22.214.171.124) catalyzes Ca2+-independent hydrolysis of the membrane lipid phosphatidylinositol (PI) to produce phosphorylated myo-inositol and diacylglycerol (DAG). The 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. In contrast, SaPLC1 is the first known natural Ca2+-dependent bacterial PI-PLC. It is more closely related to the eukaryotic PI-PLCs rather than the typical bacterial PI-PLCs. It participates in PI metabolism to generate myo-inositol-1-phosphate and myo-inositol-1:2-cyclic phosphate simultaneously. SaPLC1 and other members in this subfamily have two Ca2+-chelating amino acid substitutions which convert them from metal-independent enzymes to metal-dependent bacterial PI-PLC. Additionally, SaPLC1 active site utilizes a mechanism of amino acid juxtaposition, swapping amino acid positions, to adapt a calcium binding pocket and maintain more ideal active site geometry to support efficient catalysis.
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:Calcium-dependent phosphatidylinositol-specific phospholipase C from Streptomyces antibioticus (saPLC1) catalyzes hydrolysis of phosphatidylinositol into inositol 1-phosphate by a unique mechanism involving formation of inositol 1,6-cyclic phosphate as an intermediate.