Evidence for the presence of heat-stable protein (HPr) and ATP-dependent HPr kinase in heterofermentative lactobacilli lacking phosphoenolpyruvate: glycose phosphotransferase activity (phosphotransferase system/protein pbosphorylation/HPr(Ser(P)J/Hpr(Ser(P)) phosphatase)

An analysis of the biochemical basis for the lack of phosphoenolpyruvate:glycose phosphotransferase ac- tivity in heterofermentative lactobacili was carried out. Ex- tracts of Lactobacillus brevis and Lactobacillus buchneri failed to reconstitute phosphotransferase activity of extracts of Staphylococcus aureus mutants impaired in the phosphotrans- ferase system due to the absence of enzyme I, enzyme flLac, or enzyme HILac activity, suggesting that these lactobacilli lack those phosphotransferase system components. In contrast, complementation tests with an extract of a S. aureus mutant deficient in heat-stable protein (HPr) indicated the presence of HPr activity in heterofermentative lactobacilli. The HPr of L. brevis was purified and shown to have properties similar to those of a typical HPr. In addition, L. brevis possesses an ATP-dependent protein kinase that phosphorylates a serine residue of the endogenous HPr as well as other HPrs of Gram-positive origin. The kinase activity is markedly stimu- lated by phosphorylated compounds related to sugar metabo- lism and is negatively modulated by orthophosphate, pyro- phosphate, or arsenate and by a low molecular weight endog- enous factor. In keeping with the idea of a regulatory role for the phosphorylation of HPr in lactobacilli, a HPr(Ser(P)) phosphatase activity in L. brevis was also demonstrated. On the basis of the finding of HPr and a system for its reversible covalent modification in an organism devoid of a functional phosphotransferase system we propose that, in lactobacilli, HPr has a role in the regulation of pathways other than the phosphotransferase system.