The phosphotransferase system of Streptomyces coelicolor IIACrr exhibits properties that resemble transport and inducer exclusion function of enzyme IIAGlucose of Escherichia coli

We have investigated the err gene of Streptomyces coelicolor that encodes a homologue of enzyme IIA(Glucose) of Escherichia coli, which, as a component of the phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS) plays a key role in carbon regulation by triggering glucose transport, carbon catabolite repression, and inducer exclusion. As in E. coli, the err gene of S. coelicolor is genetically associated with the ptsI gene that encodes the general phosphotransferase enzyme I. The gene product IIA(Crr) was overproduced, purified, and polyclonal antibodies were obtained. Western blot analysis revealed that IIA(Crr) is expressed in vivo. The functionality of IIA(Crr) was demonstrated by phosphoenolpyruvate-dependent phosphorylation via enzyme I and the histidine-containing phosphoryl carrier protein HPr. Phosphorylation was abolished when His72, which corresponds to the catalytic histidine of E. coli IIA(Glucose), was mutated. The capacity of IIA(Crr) to operate in sugar transport was shown by complementation of the E. coli glucose-PTS. The striking functional resemblance between IIA(Crr) and IIA(Glucose) was further demonstrated by its ability to confer inducer exclusion of maltose to E. coli. A specific interaction of IIA(Crr) with the maltose permease subunit MalK from Salmonella typhimurium was uncovered by surface plasmon resonance. These data suggest that this IIA(Gluose)-like protein may be involved in carbon metabolism in S. coelicolor.