Glucose transport by a mutant of Streptococcus mutans unable to accumulate sugars via the phosphoenolpyruvate phosphotransferase system

Abstract

Streptococcus mutans transports glucose via the phosphoenolpyruvate (PEP)-dependent sugar phosphotransferase system (PTS). Earlier studies indicated that an alternate glucose transport system functions in this organism under conditions of high growth rates, low pH, or excess glucose. To identify this system, S. mutans BM71 was transformed with integration vector pDC-5 to generate a mutant, DC10, defective in the general PTS protein enzyme I (EI . Sugar competition experiments with DC10 indicated that the non-PTS transport system had high specificity for glucose since glucose transport was not significantly inhibited by a 100-fold molar excess of several competing sugar substrates, including 2-deoxyglucose and ␣-methylglucoside. These results demonstrate that S. mutans possesses a glucose transport system that can function independently of the PEP PTS.Carbohydrate metabolism by Streptococcus mutans results in the formation of acid end products that can contribute to the demineralization of tooth enamel, leading to dental caries (11, 42). The phosphoenolpyruvate (PEP)-dependent sugar phosphotransferase system (PTS) (29) is the principal transport process in oral streptococci for glucose and a variety of sugars, including mannose, fructose, sucrose, lactose, and maltose (2, 17, 37). In the PTS, phosphate is transferred from PEP via the general PTS proteins HPr and EI to the sugar-specific, membrane-bound protein EII and then to the incoming sugar. Much of the current information on the structure of the PTS has come from work with Escherichia coli and Salmonella typhimurium, particularly with respect to the various sugar-specific EIIs (29). The arrangement of the domains that make up the EIIs can vary depending on the organism and the sugar to be transported, appearing either (i) as a single membranebound protein consisting of three domains (A, B, and C); (ii) as two or more proteins, one of which is membrane bound (B and C) and one of which is soluble (IIA or EIII); (iii) with domains A and B fused into a single soluble protein and associated with two membrane components (C and D); or (iv) with domains IIA and IIB existing as separate soluble proteins (29,34). While other variations in the domain organization are known, phosphoryl transfer generally occurs sequentially via EI, HPr, EIIA, and EIIB, with the EIIC and EIID components probably forming a translocation channel in the membrane.With respect to S. mutans, information is available on the genetic arrangement of some, but not all, of the PTS and associated components responsible for the transport of sucrose (scrA) (35) and mannitol (20). More complete information is available on the lactose operon in this organism, including the nucleotide and deduced amino acid sequences of the repressor, the tagatose-6-phosphate pathway, and IIA Lac (lacF) and IICB Lac (lacE) of the PTS (30). A more recent report (21) has indicated that the gene for phospho-␤-galactosidase (lacG), the enzyme that cleaves lactose phosphate that is generated by the lactose PTS, is also locate...

The HPr protein of the phosphotransferase system links induction and catabolite repression of the Bacillus subtilis levanase operon

“…All strains contain a p⌬B (Ϫ148, ϩ189) levDЈ-ЈlacZ translational fusion (38) subtilis. The existence of such a system has recently been described for the gram-positive bacterium Streptococcus mutans (6). Effect of point mutations in the ptsH gene encoding the HPr protein on the regulation of the levanase operon.…”

Up-regulation of competence- but not stress-responsive proteins accompanies an altered metabolic phenotype in Streptococcus mutans biofilms

“…Notwithstanding, neither this nor previous 2-DGE analyses (Len et al, 2003(Len et al, , 2004b have identified the integral cytoplasmic membrane glucose transporters EII man and EII glc , or the glucose permease of S. mutans required for uptake of glucose (Cvitkovitch et al, 1995;Vadeboncoeur et al, 1991) due to their hydrophobic structure. As a consequence, any change that the level of expression of these transporters may have on glucose uptake and subsequent metabolic rate cannot be surmised.…”

Proteome analysis of Streptococcus mutans metabolic phenotype during acid tolerance

“…However, continuous-culture studies suggest that S. mutans is completely devoid of EII man and EII glc activity at pH 5?0 (Vadeboncoeur et al, 1991). At this acid pH, the bacterium preferentially utilizes a non-PTS glucose permease system (Hamilton & St Martin, 1982;Dashper & Reynolds, 1990;Buckley & Hamilton, 1994), while maintaining a more alkaline cytoplasm by increasing the level of its proton-translocating F 1 F 0 -ATPase (Hamilton & Buckley, 1991;Cvitkovitch et al, 1995). The recent annotation of the S. mutans genome, however, does not identify a gene encoding a specific glucose permease (Ajdić et al, 2002).…”