Abstract
In Streptococcus salivarius, the phosphoenolpyruvate (PEP):mannose-glucose phosphotransferase system, which concomitantly transports and phosphorylates mannose, glucose, fructose, and 2-deoxyglucose, is composed of the general energy-coupling proteins EI and HPr, the specific membrane-bound IIIMan, and two forms of a protein called IIIMan, with molecular weights of 38,900 (IIIManH) and 35,200 (IIIManL), that are found in the cytoplasm as well as associated with the membrane. Several lines of evidence suggest that IIIManH and/or IIIManL are involved in the control of sugar metabolism. To determine whether other bacteria possess these proteins, we tested for their presence in 28 oral streptococcus strains, 3 nonoral streptococcus strains, 2 lactococcus strains, 2 enterococcus strains, 2 bacillus strains, 1 lactobacillus strain, Staphylococcus aureus, and Escherichia coli. Three approaches were used to determine whether the IIIMan proteins were present in these bacteria: (i) Western blot (immunoblot) analysis of cytoplasmic and membrane proteins, using anti-IIIManH and anti-IIIManH rabbit polyclonal antibodies; (ii) analysis of PEP-dependent phosphoproteins by polyacrylamide gel electrophoresis; and (iii) inhibition by anti-IIIMan antibodies of the PEP-dependent phosphorylation of 2-deoxyglucose (a mannose analog) by crude cellular extracts. Only the species S. salivarius and Streptococcus vestibularis possessed the two forms of IIIMan. Fifteen other streptococcal species possessed one protein with a molecular weight between 35,200 and 38,900 that cross-reacted with both antibodies. In the case of 9 species, a protein possessing the same electrophoretic mobility was phosphorylated at the expense of PEP. No such phosphoprotein, however, could be detected in the other six species. A III(Man)-like protein with a molecular weight of 35,500 was also detected in Lactobacillus casei by Western blot experiments as well as by PEP-dependent phosphoprotein analysis, and a protein with a molecular weight of 38,900 that cross-reacted with anti-III(Man) antibodies was detected in Lactococcus lactis. In several cases, the involvement of these putative III(Man) proteins in the PEP-dependent phosphorylation of 2-deoxyglucose was substantiated by the inhibition of phosphorylation activity of anti-III(Man) antibodies. No proteins cross-reacting with anti-III(Man) antibodies were detected in enterococci, bacilli, and E. coli. In S. aureus, a membrane protein with a molecular weight of 50,000 reacted strongly with the antibodies. This protein, however, was not phosphorylated at the expense of PEP.