Phosphorylation of Streptococcus salivarius lactose permease (LacS) by HPr(His ~ P) and HPr(Ser-P)(His ~ P) and effects on growth.
The oral bacterium Streptococcus salivarius takes up lactose via a transporter called LacS that shares 95% identity with the LacS from Streptococcus thermophilus, a phylogenetically closely related organism. S. thermophilus releases galactose into the medium during growth on lactose. Expulsion of galactose is mediated via LacS and stimulated by phosphorylation of the transporter by HPr(His approximately P), a phosphocarrier of the phosphoenolpyruvate:sugar phosphotransferase transport system (PTS). Unlike S. thermophilus, S. salivarius grew on lactose without expelling galactose and took up galactose and lactose concomitantly when it is grown in a medium containing both sugars. Analysis of the C-terminal end of S. salivarius LacS revealed a IIA-like domain (IIA(LacS)) almost identical to the IIA domain of S. thermophilus LacS. Experiments performed with purified proteins showed that S. salivarius IIA(LacS) was reversibly phosphorylated on a histidine residue at position 552 not only by HPr(His approximately P) but also by HPr(Ser-P)(His approximately P), a doubly phosphorylated form of HPr present in large amounts in rapidly growing S. salivarius cells. Two other major S. salivarius PTS proteins, IIAB(L)(Man) and IIAB(H)(Man), were unable to phosphorylate IIA(LacS). The effect of LacS phosphorylation on growth was studied with strain G71, an S. salivarius enzyme I-negative mutant that cannot synthesize HPr(His approximately P) or HPr(Ser-P)(His approximately P). These results indicated that (i) the wild-type and mutant strains had identical generation times on lactose, (ii) neither strain expelled galactose during growth on lactose, (iii) both strains metabolized lactose and galactose concomitantly when grown in a medium containing both sugars, and (iv) the growth of the mutant was slightly reduced on galactose.
Lessard
Christian
C
Groupe de Recherche en Ecologie Buccale, Département de Biochimie et de Microbiologie, Faculté des Sciences et de Génie, and Faculté de Médecine Dentaire, Université Laval, Québec City, Quebec G1K 7P4, Canada.
Cochu
Armelle
A
Lemay
Jean-Dominique
JD
Roy
Denis
D
Vaillancourt
Katy
K
Frenette
Michel
M
Moineau
Sylvain
S
Vadeboncoeur
Christian
C
D001345:Autoradiography; D001426:Bacterial Proteins; D003470:Culture Media; D004591:Electrophoresis, Polyacrylamide Gel; D029968:Escherichia coli Proteins; D005690:Galactose / Q000378:metabolism; D007785:Lactose / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000032:analysis / Q000378:metabolism / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000032:analysis / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013291:Streptococcus / Q000254:growth & development / Q000378:metabolism*; D027981:Symporters
D001426:Bacterial Proteins; D003470:Culture Media; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D011994:Recombinant Proteins; D027981:Symporters; C021499:lactose permease; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C030182:phosphocarrier protein HPr; D010749:Phosphoprotein Phosphatases; D007785:Lactose; D005690:Galactose