Characterization of an HPr kinase mutant of Staphylococcus xylosus

The Staphylococcus xylosus gene hprK, encoding HPr kinase (HPrK), has been isolated from a genomic library. The HPrK enzyme, purified as a His(6) fusi on protein, phosphorylated HPr, the phosphocarrier protein of the bacterial phosphotransferase system, at a serine residue in an ATP-dependent manner, and it also catalyzed the reverse reaction. Therefore, the enzyme constitu tes a bifunctional HPr kinase/phosphatase, Insertional inactivation of the gene in the genome of S. xylosus resulted in the concomitant loss of both H Pr kinase and His serine-phosphorylated-HPr phosphatase activities in cell extracts, strongly indicating that the HPrK enzyme is also responsible for both reactions in vivo. HPrK deficiency had a profound pleiotropic effect o n the physiology of S. xylosus, The hprK mutant strain showed a severe grow th defect in complex medium upon addition of glucose. Glucose uptake in glu cose-grown cells was strongly enhanced compared with the wild type. Carbon catabolite repression of three tested enzyme activities by glucose, sucrose , and fructose was abolished. These results clearly demonstrate the promine nt role of HPr kinase in global control to adjust catabolic capacities of S . xylosus according to the availability of preferred carbon sources.