Regulatory functions of serine-46-phosphorylated HPr in Lactococcus lactis.
In most low-G+C gram-positive bacteria, the phosphoryl carrier protein HPr of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) becomes phosphorylated at Ser-46. This ATP-dependent reaction is catalyzed by the bifunctional HPr kinase/P-Ser-HPr phosphatase. We found that serine-phosphorylated HPr (P-Ser-HPr) of Lactococcus lactis participates not only in carbon catabolite repression of an operon encoding a beta-glucoside-specific EII and a 6-P-beta-glucosidase but also in inducer exclusion of the non-PTS carbohydrates maltose and ribose. In a wild-type strain, transport of these non-PTS carbohydrates is strongly inhibited by the presence of glucose, whereas in a ptsH1 mutant, in which Ser-46 of HPr is replaced with an alanine, glucose had lost its inhibitory effect. In vitro experiments carried out with L. lactis vesicles had suggested that P-Ser-HPr is also implicated in inducer expulsion of nonmetabolizable homologues of PTS sugars, such as methyl beta-D-thiogalactoside (TMG) and 2-deoxy-D-glucose (2-DG). In vivo experiments with the ptsH1 mutant established that P-Ser-HPr is not necessary for inducer expulsion. Glucose-activated 2-DG expulsion occurred at similar rates in wild-type and ptsH1 mutant strains, whereas TMG expulsion was slowed in the ptsH1 mutant. It therefore seems that P-Ser-HPr is not essential for inducer expulsion but that in certain cases it can play an indirect role in this regulatory process.
Monedero
V
V
Laboratoire de Génétique des Microorganismes, INRA-CNRS URA 1925, 78850 Thiverval-Grignon, France.
Kuipers
O P
OP
Jamet
E
E
Deutscher
J
J
D001426:Bacterial Proteins; D003470:Culture Media; D004790:Enzyme Induction; D004794:Enzyme Repression; D015964:Gene Expression Regulation, Bacterial; D005947:Glucose / Q000378:metabolism*; D005960:Glucosides / Q000378:metabolism; D013294:Lactococcus lactis / Q000235:genetics / Q000378:metabolism*; D008320:Maltose / Q000378:metabolism; D009154:Mutation; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000235:genetics* / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D012266:Ribose / Q000378:metabolism
D001426:Bacterial Proteins; D003470:Culture Media; D005960:Glucosides; D012266:Ribose; D008320:Maltose; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C030182:phosphocarrier protein HPr; D005947:Glucose