Journal of Bacteriology, May 2000, p. 2582-2590, Vol. 182, No. 9
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Laboratoire de Génétique des Microorganismes, 78850 Thiverval-Grignon,1 Laboratoire de Recherche sur la Viande, 78352 Jouy-en-Josas,2 and Institut de Biologie et Chimie des Protéines, 69367 Lyon,3 France, and Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de Alimentos, 46100 Burjasot, Valencia, Spain4
Received 23 November 1999/Accepted 9 February 2000
We have cloned and sequenced the Lactobacillus casei
hprK gene encoding the bifunctional enzyme HPr kinase/P-Ser-HPr
phosphatase (HprK/P). Purified recombinant L. casei HprK/P
catalyzes the ATP-dependent phosphorylation of HPr, a phosphocarrier
protein of the phosphoenolpyruvate:carbohydrate phosphotransferase
system at the regulatory Ser-46 as well as the dephosphorylation of
seryl-phosphorylated HPr (P-Ser-HPr). The two opposing activities of
HprK/P were regulated by fructose-1,6-bisphosphate, which stimulated
HPr phosphorylation, and by inorganic phosphate, which stimulated the
P-Ser-HPr phosphatase activity. A mutant producing truncated HprK/P was
found to be devoid of both HPr kinase and P-Ser-HPr phosphatase
activities. When hprK was inactivated, carbon catabolite
repression of N-acetylglucosaminidase disappeared, and the
lag phase observed during diauxic growth of the wild-type strain on
media containing glucose plus either lactose or maltose was strongly
diminished. In addition, inducer exclusion exerted by the presence of
glucose on maltose transport in the wild-type strain was abolished in
the hprK mutant. However, inducer expulsion of
methyl
-D-thiogalactoside triggered by
rapidly metabolizable carbon sources was still operative in
ptsH mutants altered at Ser-46 of HPr and the
hprK mutant, suggesting that, in contrast to the model
proposed for inducer expulsion in gram-positive bacteria, P-Ser-HPr
might not be involved in this regulatory process.
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