Regulation of the glucose-specific phosphotransferase system (PTS) of Staphylococcus carnosus by the antiterminator protein GlcT.

The ptsG operon of Staphylococcus carnosus consists of two adjacent genes, glcA and glcB, encoding glucose- and glucoside-specific enzymes II, respectively, the sugar permeases of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). The expression of the ptsG operon is glucose-inducible. Putative RAT (ribonucleic antiterminator) and terminator sequences localized in the promoter region of glcA suggest regulation via antitermination. The glcT gene was cloned and the putative antiterminator protein GlcT was purified. Activity of this protein was demonstrated in vivo in Escherichia coli and Bacillus subtilis. In vitro studies led to the assumption that phosphoenolpyruvate-dependent phosphorylation of residue His105 via the general PTS components enzyme I and HPr facilitates dimerization of GlcT and consequently activation. Because of the high similarity of the two ptsG-RAT sequences of B. subtilis and S. carnosus, in vivo studies were performed in B. subtilis. These indicated that GlcT of S. carnosus is able to recognize ptsG-RAT sequences of B. subtilis and to cause antitermination. The specific interaction between B. subtilis ptsG-RAT and S. carnosus GlcT demonstrated by surface plasmon resonance suggests that only the dimer of GlcT binds to the RAT sequence. HPr-dependent phosphorylation of GlcT facilitates dimer formation and may be a control device for the proper function of the general PTS components enzyme I and HPr necessary for glucose uptake and phosphorylation by the corresponding enzyme II.