Phosphatidylinositol-Specific Phospholipase C of Bacillus cereus: Cloning, Sequencing, and Relationship to Other Phospholipases

Abstract

The phosphatidylinositol (Pl)-specific phospholipase C (PLC) of Bacillus cereuswas cloned into Escherichia coli by using monoclonal antibody probes raised against the purified protein. The enzyme is specific for hydrolysis of the membrane lipid PI and Pl-glycan-containing membrane anchors, which are important structural componentsof one class of membrane proteins. The protein expressedin E. colicomigrated with B. cereus PI-PLC in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, as detected by immunoblotting, and conferred PI-PLC activity on the host. This enzyme activity was inhibited by PI-PLC-specific monoclonal antibodies. The nucleotide sequence of the PI-PLC gene suggests that this secreted bacterial protein is synthesized as a larger precursor with a 31-amino-acid N-terminal extension to the mature enzyme of 298 amino acids. From analysis of coding and flanking sequences of the gene, weconclude that the PI-PLC gene does not reside next to the gene cluster of the other two secreted phospholipases C on the bacterial chromosome. The deduced amino acid sequence of the B. cereus PI-PLC contains a stretch of significant similarity to the glycosylphosphatidylinositol-specific PLCof Trypanosoma brucei. The conserved peptide is proposed to playa role in the function of these enzymes.