Phosphorylation of Streptococcus salivarius Lactose Permease (LacS) by HPr(His∼P) and HPr(Ser-P)(His∼P) and Effects on Growth

Abstract

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(HisϳP), 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. The effect of LacS phosphorylation on growth was studied with strain G71, an S. salivarius enzyme I-negative mutant that cannot synthesize HPr(HisϳP) or HPr(Ser-P)(HisϳP). 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.Streptococcus salivarius is the predominant bacterial species among the pioneer microorganisms that colonize the mouth (19). Acquisition of and competition for nutrients, particularly sugars, which serve as the major energy source for oral streptococci, constitute vital ecological determinants for the survival of oral bacteria. S. salivarius is able to metabolize a broad variety of sugars that can be grouped into two categories, non-PTS sugars, which are taken up by transport systems energized by proton motive force or ATP, and PTS sugars, which are transported by the phosphoenolpyruvate:sugar phosphotransferase system (PTS) (4,35,38). The PTS uses phosphoenolpyruvate (PEP) in a group translocation process to phosphorylate incoming mono-and disaccharides via a phosphoryl-transfer cascade involving the non-sugar-specific proteins, Enzyme I (EI) and HPr, and a family of sugar-specific enzyme II complexes (EII) (27). In gram-positive bacteria, the PTS controls sugar metabolism by regulating transporter activities and gene transcription via the protein HPr (6, 29). This protein can be phosphorylated by EI at the expense of PEP on a histidine at position 15, generating HPr(HisϳP), and by a ATP-dependent protein kinase/phosphorylase, called HPrK/P, on a serine at position 46, generating HPr(Ser-P) (6,8,29). Both HPr(HisϳP) and HPr(Ser-P) possess regulatory functions. HPr(HisϳP) accomplishes its regulatory functions by reversibly phosphorylating its targets, and HPr(Ser-P) accomplishes its regulatory functions by protein-protein interactions (7,13,31,42). In addition to the aforementioned phosphorylated forms of HPr, rapidly growing streptococcal cells contain substantial amounts of the doubly phosphorylated form HPr(Ser-P)(HisϳP), whose functions remain unclear (33,36,37).Lactose (milk sugar) is a disacc...

Global analysis of carbohydrate utilization by Lactobacillus acidophilus using cDNA microarrays

“…LacS is similar to GPH permeases previously identified in lactic acid bacteria (18)(19)(20). Although LacS contains a EIIA at the carboxy terminus, it is not a PTS transporter.…”

“…Members of the LacS subfamily of GPH translocators have been described in a variety of lactic acid bacteria, including Leuconostoc lactis (26), S. thermophilus (27), S. salivarius (19), Lactobacillus delbrueckii (28), and Lactobacillus helveticus (20). LacS has been reported to have the ability to import both galactose and lactose in select organisms (26,27).…”

“…Although LacS contains a EIIA at the carboxy terminus, it is not a PTS transporter. In addition, LacS includes a His at position 560, which might be involved in interaction with HPr, as shown in Streptococcus salivarius (19). In the presence of lactose and galactose, galKTM was induced between 3.7-and 17.6-fold; lacSZ was induced between 2.8-and 17.6-fold; lacL and galE were induced between 2.7 and 29.5 when compared with other carbohydrates not containing galactose, i.e., glucose, fructose, sucrose, trehalose, and FOS.…”

How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria

“…In vitro studies revealed that LacS of S. thermophilus and S. salivarius becomes efficiently phosphorylated at His-552 not only by PϳHis-HPr but also by doubly phosphorylated (PϳHis,P-Ser)-HPr (134,468), which is present in large amounts in oral streptococci grown on glucose or lactose (660,893) and in lactose-grown S. thermophilus cells (134). However, in contrast to S. thermophilus, S. salivarius did not expel galactose during growth on lactose.…”

The Bacterial Phosphoenolpyruvate:Carbohydrate Phosphotransferase System: Regulation by Protein Phosphorylation and Phosphorylation-Dependent Protein-Protein Interactions

“…The export of galactose is coupled to the uptake of lactose via a counterflow mechanism. Phosphorylation of the EIIA Glc -like domain of LacS was demonstrated for S. thermophilus (60) and S. salivarius (61). It increases the affinity of LacS for its substrate and the speed of the counterflow reaction (62).…”