Enzyme IIIlac of the staphylococcal phosphoenolpyruvate-dependent phosphotransferase system: site-specific mutagenesis of histidine residues, biochemical characterization and 1H-NMR studies

The lactose-specific pbosphocarrier protein enzyme III of thebacterial phosphoenol-pyruvate-dependent phosphotransferasesystem of Staphylococcus aureus was modified by sitespecificmutagenesis on the corresponding lacF gene in order to replacethe histidine residues 78 and 82 of the amino acid sequencewith a serine residue. Wild-type and both mutant genes wereoverexpressed in Escherichia coli and the gene products werepurified to homogeneity. The conformation of wild-type and mutantproteins were monitored by ¹H-NMR spectroscopy. In vitro phosphorylationstudies on mutant lactose-specific enzyme III, as well as evidencefrom NMR spectroscopy, lead to the conclusion that His78 isthe activesite for phosphorylation of lactose-specific enzymeIII by phospho-HPr (histidine-containing protein). The roleof His82 probably is the enhancement of velocity and efficiencyof the phosphotransfer from lactose-specific enzyme in to lactosespecifkenzyme II. This result refutes the conclusion of former workbased on data by protelytk cleavage and sequencing of the ³²P-labeledpeptide of lactose-specific enzyme DTI that His82 is the active-sitefor phosphorylation.