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1.  Characterization of Streptococcus mutans Strains Deficient in EIIABMan of the Sugar Phosphotransferase System 
The phosphoenolpyruvate:sugar phosphotransferase system (PTS) is the major sugar uptake system in oral streptococci. The role of EIIABMan (encoded by manL) in gene regulation and sugar transport was investigated in Streptococcus mutans UA159. The manL knockout strain, JAM1, grew more slowly than the wild-type strain in glucose but grew faster in mannose and did not display diauxic growth, indicating that EIIABMan is involved in sugar uptake and in carbohydrate catabolite repression. PTS assays of JAM1, and of strains lacking the inducible (fruI) and constitutive (fruCD) EII fructose, revealed that S. mutans EIIABMan transported mannose and glucose and provided evidence that there was also a mannose-inducible or glucose-repressible mannose PTS. Additionally, there appears to be a fructose PTS that is different than FruI and FruCD. To determine whether EIIABMan controlled expression of the known virulence genes, glucosyltransferases (gtfBC) and fructosyltransferase (ftf) promoter fusions of these genes were established in the wild-type and EIIABMan-deficient strains. In the manL mutant, the level of chloramphenicol acetyltransferase activity expressed from the gtfBC promoter was up to threefold lower than that seen with the wild-type strain at pH 6 and 7, indicating that EIIABMan is required for optimal expression of gtfBC. No significant differences were observed between the mutant and the wild-type background in ftf regulation, with the exception that under glucose-limiting conditions at pH 7, the mutant exhibited a 2.1-fold increase in ftf expression. Two-dimensional gel analysis of batch-grown cells of the EIIABMan-deficient strain indicated that the expression of at least 38 proteins was altered compared to that seen with the wild-type strain, revealing that EIIABMan has a pleiotropic effect on gene expression.
PMCID: PMC169087  PMID: 12902269
2.  The EIIABMan Phosphotransferase System Permease Regulates Carbohydrate Catabolite Repression in Streptococcus gordonii▿ †  
Commensal oral streptococci play critical roles in oral biofilm formation and promote dental health by competing with, and antagonizing the growth of, pathogenic organisms, such as Streptococcus mutans. Efficient utilization of the spectrum of carbohydrates in the oral cavity by commensal streptococci is essential for their persistence, and yet very little is known about the regulation of carbohydrate catabolism by these organisms. Carbohydrate catabolite repression (CCR) in the abundant oral commensal Streptococcus gordonii strain DL-1 was investigated using the exo-β-d-fructosidase gene (fruA) and a fructose/mannose sugar:phosphotransferase (PTS) enzyme II operon (levDEFG) as model systems. Functional studies confirmed the predicted roles of FruA and LevD in S. gordonii. ManL, the AB domain of a fructose/mannose-type enzyme II PTS permease, contributed to utilization of glucose, mannose, galactose, and fructose and exerted primary control over CCR of the fruA and levD operons. Unlike in S. mutans, ManL-dependent CCR was not sugar specific, and galactose was very effective at eliciting CCR in S. gordonii. Inactivation of the apparent ccpA homologue of S. gordonii actually enhanced CCR of fruA and levD, an effect likely due to its demonstrated role in repression of manL expression. Thus, there are some similarities and fundamental differences in CCR control mechanisms between the oral pathogen S. mutans and the oral commensal S. gordonii that may eventually be exploited to enhance the competitiveness of health-associated commensals in oral biofilms.
PMCID: PMC3067331  PMID: 21239541
3.  Regulation of the Bacillus subtilis GlcT Antiterminator Protein by Components of the Phosphotransferase System 
Journal of Bacteriology  1998;180(20):5319-5326.
Bacillus subtilis utilizes glucose as the preferred source of carbon and energy. The sugar is transported into the cell by a specific permease of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) encoded by the ptsGHI operon. Expression of this operon is induced by glucose and requires the action of a positive transcription factor, the GlcT antiterminator protein. Glucose availability is sensed by glucose-specific enzyme II (EIIGlc), the product of ptsG. In the absence of inducer, the glucose permease negatively controls the activity of the antiterminator. The GlcT antiterminator has a modular structure. The isolated N-terminal part contains the RNA-binding protein and acts as a constitutively acting antiterminator. GlcT contains two PTS regulation domains (PRDs) at the C terminus. One (PRD-I) is the target of negative control exerted by EIIGlc. A conserved His residue (His-104 in GlcT) is involved in inactivation of GlcT in the absence of glucose. It was previously proposed that PRD-containing transcriptional antiterminators are phosphorylated and concomitantly inactivated in the absence of the substrate by their corresponding PTS permeases. The results obtained with B. subtilis glucose permease with site-specific mutations suggest, however, that the permease might modulate the phosphorylation reaction without being the phosphate donor.
PMCID: PMC107579  PMID: 9765562
4.  Effect of growth conditions on levels of components of the phosphoenolpyruvate:sugar phosphotransferase system in Streptococcus mutans and Streptococcus sobrinus grown in continuous culture. 
Journal of Bacteriology  1987;169(12):5686-5691.
The membrane-bound, sugar-specific enzyme II (EII) component of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) in Streptococcus mutans Ingbritt is repressed by growth on glucose under various conditions in continuous culture. Compared with optimal PTS conditions (i.e., glucose limitation, dilution rate [D] of 0.1 h-1, and pH 7.0), EII activity for glucose (EIIGlc) and mannose (EIIMan) in cells grown at a D of 0.4 h-1 and pH 5.5 with the same glucose concentration was reduced 24- to 27-fold. EII activity with methyl alpha-glucoside and 2-deoxyglucose was reduced 6- and 26-fold, respectively. Growth with excess glucose (i.e., nitrogen limitation) resulted in 26- to 88-fold repression of EII activity with these substrates. The above conditions of low pH, high dilution rate, and excess glucose also repressed EII activity for fructose (EIIFru), but to a lesser extent (two- to fivefold). Conversely, growth of S. mutans DR0001 at a D of 0.2 h-1 and pH 5.5 resulted in increased EIIGlc and EIIMan activity. Unlike the EII component, the HPr concentration in S. mutans Ingbritt varied only twofold (5.5 to 11.4 nmol/mg of protein) despite growth at pH 5.5 with limiting and excess glucose. The HPr concentrations in S. mutans DR0001 and the glucose-PTS-defective mutant DR0001/6 were similar. In a companion study, the soluble components of the PTS (i.e., HPr, EI, and EIIILac) in Streptococcus sobrinus grown on limiting lactose in a chemostat were not influenced significantly by growth at various pHs (7.0 and 5.0) and growth rates (D of 0.1, 0.54, and 0.8 h-1). However, growth on lactose resulted in repression of both EIIGlc and EIIFru, confirming earlier results with batch-grown cells. Thus, the glucose-PTS in some strains of S. mutans is regulated at the level of EII synthesis by certain environmental conditions.
PMCID: PMC214049  PMID: 3680174
5.  Concentration-dependent repression of the soluble and membrane components of the Streptococcus mutans phosphoenolpyruvate: sugar phosphotransferase system by glucose. 
Journal of Bacteriology  1989;171(6):2942-2948.
Growth of Streptococcus mutans Ingbritt in continuous culture (pH 7.0, dilution rate of 0.1 h-1) at medium glucose concentrations above 2.6 mM resulted in repression of the sugar-specific membrane components, enzyme IIGlc (EIIGlc) and EIIMan, of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). In one experiment, significant repression (27-fold) was observed with 73 mM glucose when the glycolytic capacity of the cells was reduced by only 2-fold and when the culture was still glucose limited. In a more comprehensive experiment in which cells were grown in continuous culture at eight glucose concentrations from 2.6 to 304 mM, in addition to repression of specific EII activities for glucose, mannose, 2-deoxyglucose, and fructose, synthesis of the general protein, EI, was repressed at all glucose levels above 2.6 mM to a maximum of 4-fold at 304 mM glucose when the culture was growing with excess glucose (i.e., nitrogen limited). The other PTS general protein, HPr, was less sensitive to the exogenous glucose level but was nevertheless repressed fourfold under glucose-excess conditions. The Km for glucose for EIIGlc increased from 0.22 mM during growth at 3.6 mM glucose (glucose limited) to 0.48 mM at 271 mM glucose (glucose excess). The shift from heterofermentation to homofermentation during growth with increasing glucose levels suggests the involvement of glycolytic intermediates, ATP, or another high-energy phosphate metabolite in regulation of the synthesis of the PTS components in S. mutans.
PMCID: PMC209998  PMID: 2722738
6.  Glucose phosphoenolpyruvate-dependent phosphotransferase system of Streptococcus mutans GS5 studied by using cell-free extracts. 
Infection and Immunity  1984;44(2):486-492.
The glucose phosphotransferase system (PTS) of Streptococcus mutans GS5 has been partially characterized, using fractions derived from cells treated with the muramidase mutanolysin. Membranes retained functional PTS enzymes for the phosphoenolpyruvate-dependent phosphorylation of glucose, fructose, and mannose. This was confirmed by assaying membranes directly for enzyme I (EI) and enzyme IIglc (EIIglc) by employing specific phosphoryl-exchange reactions for each factor. Membranes prepared from glucose PTS- mutants, however, were either deficient in glucose phosphorylation or reflected the "leakiness" displayed by whole cells. Mutant membranes were unable to catalyze the glucose:glucose 6-phosphate transphosphorylation reaction, indicating a defective EIIglc in these fractions. Although total cellular EI activities in the mutant clones were about the same as that measured for the wild-type strain by employing the pyruvate:phosphoenolpyruvate phosphoryl-exchange reaction, mutant membranes were found to possess less than 10% of the specific EI activity of wild-type membranes. The cytoplasmic fractions of mutants, however, displayed markedly increased specific activities for this enzyme when compared with wild-type extracts. These results strongly suggest a molecular association of EI with a normal membrane protein, perhaps EIIglc, that is absent in mutants. This would explain the absence of fructose PTS activity in glucose PTS- mutant membranes despite the fact that whole cells of these clones are normal for this transport function.
PMCID: PMC263546  PMID: 6715047
7.  Mlc of Thermus thermophilus: a Glucose-Specific Regulator for a Glucose/Mannose ABC Transporter in the Absence of the Phosphotransferase System 
Journal of Bacteriology  2006;188(18):6561-6571.
We report the presence of Mlc in a thermophilic bacterium. Mlc is known as a global regulator of sugar metabolism in gram-negative enteric bacteria that is controlled by sequestration to a glucose-transporting EIIGlc of the phosphotransferase system (PTS). Since thermophilic bacteria do not possess PTS, Mlc in Thermus thermophilus must be differently controlled. DNA sequence alignments between Mlc from T. thermophilus (MlcTth) and Mlc from E. coli (MlcEco) revealed that MlcTth conserved five residues of the glucose-binding motif of glucokinases. Here we show that MlcTth is not a glucokinase but is indeed able to bind glucose (KD = 20 μM), unlike MlcEco. We found that mlc of T. thermophilus is the first gene within an operon encoding an ABC transporter for glucose and mannose, including a glucose/mannose-binding protein and two permeases. malK1, encoding the cognate ATP-hydrolyzing subunit, is located elsewhere on the chromosome. The system transports glucose at 70°C with a Km of 0.15 μM and a Vmax of 4.22 nmol per min per ml at an optical density (OD) of 1. MlcTth negatively regulates itself and the entire glucose/mannose ABC transport system operon but not malK1, with glucose acting as an inducer. MalK1 is shared with the ABC transporter for trehalose, maltose, sucrose, and palatinose (TMSP). Mutants lacking malK1 do not transport either glucose or maltose. The TMSP transporter is also able to transport glucose with a Km of 1.4 μM and a Vmax of 7.6 nmol per min per ml at an OD of 1, but it does not transport mannose.
PMCID: PMC1595481  PMID: 16952948
8.  Genetic Analysis of the Functions and Interactions of Components of the LevQRST Signal Transduction Complex of Streptococcus mutans 
PLoS ONE  2011;6(2):e17335.
Transcription of the genes for a fructan hydrolase (fruA) and a fructose/mannose sugar:phosphotransferase permease (levDEFG) in Streptococcus mutans is activated by a four-component regulatory system consisting of a histidine kinase (LevS), a response regulator (LevR) and two carbohydrate-binding proteins (LevQT). The expression of the fruA and levD operons was at baseline in a levQ mutant and substantially decreased in a levT null mutant, with lower expression with the cognate inducers fructose or mannose, but slightly higher expression in glucose or galactose. A strain expressing levQ with two point mutations (E170A/F292S) did not require inducers to activate gene expression and displayed altered levD expression when growing on various carbohydrates, including cellobiose. Linker-scanning (LS) mutagenesis was used to generate three libraries of mutants of levQ, levS and levT that displayed various levels of altered substrate specificity and of fruA/levD gene expression. The data support that LevQ and LevT are intimately involved in the sensing of carbohydrate signals, and that LevQ appears to be required for the integrity of the signal transduction complex, apparently by interacting with the sensor kinase LevS.
PMCID: PMC3043104  PMID: 21364902
9.  Global Transcriptional Analysis of Streptococcus mutans Sugar Transporters Using Microarrays▿ † 
Journal of Bacteriology  2007;189(14):5049-5059.
The transport of carbohydrates by Streptococcus mutans is accomplished by the phosphoenolpyruvate-phosphotransferase system (PTS) and ATP-binding cassette (ABC) transporters. To undertake a global transcriptional analysis of all S. mutans sugar transporters simultaneously, we used a whole-genome expression microarray. Global transcription profiles of S. mutans UA159 were determined for several monosaccharides (glucose, fructose, galactose, and mannose), disaccharides (sucrose, lactose, maltose, and trehalose), a β-glucoside (cellobiose), oligosaccharides (raffinose, stachyose, and maltotriose), and a sugar alcohol (mannitol). The results revealed that PTSs were responsible for transport of monosaccharides, disaccharides, β-glucosides, and sugar alcohol. Six PTSs were transcribed only if a specific sugar was present in the growth medium; thus, they were regulated at the transcriptional level. These included transporters for fructose, lactose, cellobiose, and trehalose and two transporters for mannitol. Three PTSs were repressed under all conditions tested. Interestingly, five PTSs were always highly expressed regardless of the sugar source used, presumably suggesting their availability for immediate uptake of most common dietary sugars (glucose, fructose, maltose, and sucrose). The ABC transporters were found to be specific for oligosaccharides, raffinose, stachyose, and isomaltosaccharides. Compared to the PTSs, the ABC transporters showed higher transcription under several tested conditions, suggesting that they might be transporting multiple substrates.
PMCID: PMC1951856  PMID: 17496079
10.  Substrate Specificity and Signal Transduction Pathways in the Glucose-Specific Enzyme II (EIIGlc) Component of the Escherichia coli Phosphotransferase System 
Journal of Bacteriology  2000;182(16):4437-4442.
Escherichia coli adapted to glucose-limited chemostats contained mutations in ptsG resulting in V12G, V12F, and G13C substitutions in glucose-specific enzyme II (EIIGlc) and resulting in increased transport of glucose and methyl-α-glucoside. The mutations also resulted in faster growth on mannose and glucosamine in a PtsG-dependent manner. By use of enhanced growth on glucosamine for selection, four further sites were identified where substitutions caused broadened substrate specificity (G176D, A288V, G320S, and P384R). The altered amino acids include residues previously identified as changing the uptake of ribose, fructose, and mannitol. The mutations belonged to two classes. First, at two sites, changes affected transmembrane residues (A288V and G320S), probably altering sugar selectivity directly. More remarkably, the five other specificity mutations affected residues unlikely to be in transmembrane segments and were additionally associated with increased ptsG transcription in the absence of glucose. Increased expression of wild-type EIIGlc was not by itself sufficient for growth with other sugars. A model is proposed in which the protein conformation determining sugar accessibility is linked to transcriptional signal transduction in EIIGlc. The conformation of EIIGlc elicited by either glucose transport in the wild-type protein or permanently altered conformation in the second category of mutants results in altered signal transduction and interaction with a regulator, probably Mlc, controlling the transcription of pts genes.
PMCID: PMC94614  PMID: 10913076
11.  Analysis of cis- and trans-Acting Factors Involved in Regulation of the Streptococcus mutans Fructanase Gene (fruA) 
Journal of Bacteriology  2002;184(1):126-133.
There are two primary levels of control of the expression of the fructanase gene (fruA) of Streptococcus mutans: induction by levan, inulin, or sucrose and repression in the presence of glucose and other readily metabolized sugars. The goals of this study were to assess the functionality of putative cis-acting regulatory elements and to begin to identify the trans-acting factors involved in induction and catabolite repression of fruA. The fruA promoter and its derivatives generated by deletions and/or site-directed mutagenesis were fused to a promoterless chloramphenicol acetyltransferase (CAT) gene as a reporter, and strains carrying the transcriptional fusions were then analyzed for CAT activities in response to growth on various carbon sources. A dyadic sequence, ATGACA(TC)TGTCAT, located at −72 to −59 relative to the transcription initiation site was shown to be essential for expression of fruA. Inactivation of the genes that encode fructose-specific enzymes II resulted in elevated expression from the fruA promoter, suggesting negative regulation of fruA expression by the fructose phosphotransferase system. Mutagenesis of a terminator-like structure located in the 165-base 5′ untranslated region of the fruA mRNA or insertional inactivation of antiterminator genes revealed that antitermination was not a mechanism controlling induction or repression of fruA, although the untranslated leader mRNA may play a role in optimal expression of fructanase. Deletion or mutation of a consensus catabolite response element alleviated glucose repression of fruA, but interestingly, inactivation of the ccpA gene had no discernible effect on catabolite repression of fruA. Accumulating data suggest that expression of fruA is regulated by a mechanism that has several unique features that distinguish it from archetypical polysaccharide catabolic operons of other gram-positive bacteria.
PMCID: PMC134753  PMID: 11741852
12.  Isolation and characterization of a mutation that alters the substrate specificity of the Escherichia coli glucose permease. 
Journal of Bacteriology  1996;178(3):940-942.
We isolated 10 mannitol-positive mutants from a mannitol-negative Escherichia coli strain. These mutations mapped within ptsG, encoding the glucose permease (EIIGlc), and resulted in a G-320-to-V substitution that allows EIIGlc to transport mannitol. Gly-320 lies within a putative transmembrane helix of EIIGlc that may be involved in substrate recognition.
PMCID: PMC177751  PMID: 8550539
13.  Changes in Biochemical and Phenotypic Properties of Streptococcus mutans during Growth with Aeration▿ † 
Oxygen has a potent influence on the expression of genes and the activity of physiological and biochemical pathways in bacteria. We have found that oxygen significantly altered virulence-related phenotypic properties of Streptococcus mutans, the primary etiological agent of human dental caries. Transport of glucose, fructose, or mannose by the sugar:phosphotransferase system was significantly enhanced by growth under aerobic conditions, whereas aeration caused an extended lag phase and slower growth of S. mutans in medium containing glucose, fructose, or mannose as the carbohydrate source. Aeration resulted in a decrease in the glycolytic rate and enhanced the production of intracellular storage polysaccharides. Although aeration decreased the acid tolerance of S. mutans, aerobically grown cells had higher F-ATPase activity. Aeration altered biofilm architecture but did not change the ability of S. mutans to interact with salivary agglutinin. Growth in air resulted in enhanced cell-associated glucosyltransferase (Gtf) activity at the expense of cell-free Gtf activity. These results demonstrate that S. mutans can dramatically alter its pathogenic potential in response to exposure to oxygen, suggesting that the phenotype of the organism may be highly variable in the human oral cavity depending on the maturity of the dental plaque biofilm.
PMCID: PMC2675223  PMID: 19251884
14.  A Novel PTS of Streptococcus mutans is Responsible for Transport of Carbohydrates with α-1,3 linkage 
Molecular oral microbiology  2012;28(2):114-128.
The most common type of carbohydrate-transport system in Streptococcus mutans is the phosphoenolpyruvate (PEP)-sugar phosphotransferase system (PTS). We previously showed that fourteen PTSs exist in S. mutans UA159 (Ajdic et al., 2002). Several studies have shown that microorganisms growing in biofilms express different genes as compared to their planktonic counterparts. In this study, we showed that one PTS of S. mutans was expressed in sucrose-grown biofilms. Furthermore, the same PTS was also responsible for the transport and metabolism of disaccharide nigerose (3-O-α-D-glucopyranosyl-D-glucose). Additionally, the results indicate that the studied PTS might be involved in the transport and metabolism of carbohydrates synthesized by glucosyltransferase B (GtfB) and glucosyltransferase C (GtfC) of S. mutans. To our knowledge, this is the first report that shows PTS transport of a disaccharide (and possibly extracellular oligosaccharides) with α-1,3 linkage.
PMCID: PMC3593818  PMID: 23193985
S. mutans; Biofilm; Transporter; Carbohydrate; Microarray
Molecular microbiology  2008;70(1):197-208.
Streptococcus mutans is particularly well-adapted for high-affinity, high-capacity catabolism of multiple carbohydrate sources. S. mutans EIILev, a fructose/mannose permease encoded by the levDEFG genes, and fruA, which encodes a hydrolase that releases fructose from fructan polymers, are transcriptionally regulated by the LevQRST four-component signal transduction system. Here, we demonstrate that (1) levDEFGX are co-transcribed and the levE/F intergenic region is required for optimal expression of levFGX; (2) D-mannose is a potent inducer of the levD and fruA operons; (3) CcpA regulates levD expression in a carbohydrate-specific manner; (4) deletion of the genes for the fructose/mannose-EII enzymes of S. mutans (manL, fruI, and levD) enhances levD expression; (5) repression of the LevQRST regulon by EII enzymes depends on the presence of their substrates and requires LevR, but not LevQST; and (6) CcpA inhibits expression of the manL and frul genes to indirectly control the LevQRST regulon. Further, the manL, ccpA, frul/fruCD and levD gene products differentially exert control over the cellobiose and lactose operons. Collectively, the results reveal the existence of a global regulatory network in S. mutans that governs the utilization of non-preferred carbohydrates in response to the availability and source of multiple preferred carbohydrates.
PMCID: PMC2583961  PMID: 18699864
Sugar:phosphotransferase system; β-D-fructosidase; Catabolite repression; CcpA; Gene regulation
16.  Identification and Characterization of a Fructose Phosphotransferase System in Bifidobacterium breve UCC2003▿  
In silico analysis of the Bifidobacterium breve UCC2003 genome allowed identification of four genetic loci, each of which specifies a putative enzyme II (EII) protein of a phosphoenolpyruvate:sugar phosphotransferase system. The EII encoded by fruA, a clear homologue of the unique EIIBCA enzyme encoded by the Bifidobacterium longum NCC2705 genome, was studied in more detail. The fruA gene is part of an operon which contains fruT, which is predicted to encode a homologue of the Bacillus subtilis antiterminator LicT. Transcriptional analysis showed that the fru operon is induced by fructose. The genetic structure, complementation studies, and the observed transcription pattern of the fru operon suggest that the EII encoded in B. breve is involved in fructose transport and that its expression is controlled by an antiterminator mechanism. Biochemical studies unequivocally demonstrated that FruA phosphorylates fructose at the C-6 position.
PMCID: PMC1796965  PMID: 17098914
17.  Effect of nutritional constraints on the biosynthesis of the components of the phosphoenolpyruvate: sugar phosphotransferase system in a fresh isolate of Streptococcus mutans. 
Infection and Immunity  1988;56(2):518-522.
A procedure for the purification of enzyme I (EI) and the protein HPr, the general components of the phosphoenolpyruvate:sugar phosphotransferase system, from Streptococcus mutans serotype c is presented. The method was also applied successfully to the purification of EI and HPr from Streptococcus salivarius, Streptococcus sobrinus, and Streptococcus sanguis. Using specific antibodies obtained against the proteins purified from S. mutans DR0001, we determined quantitatively by rocket electrophoresis the cellular levels of EI and HPr in a freshly isolated strain of S. mutans grown under various conditions in continuous culture. The activity of a few specific EIIs was also determined by an in vitro phosphorylation test. Results indicated that maximum EII activities for glucose, mannose, and 2-deoxyglucose were obtained under conditions of glucose limitation, at pH 7.0 and low dilution rate (D = 0.057/h). Increasing the amount of glucose or the dilution rate (D = 0.40/h) or decreasing the pH from 7.0 to 5.5 resulted in a 1.4- to 24-fold decrease in these activities. The EII activity for fructose was not influenced by the growth conditions in the same way as the other EIIs. The fructose EII was highest at pH 5.5 and at high dilution rate under conditions of glucose or nitrogen limitation and was always repressed at pH 7.0 and at low dilution rates. The intracellular levels of EI were also dependent on the growth conditions. The highest concentration (0.65 nmol/mg of protein) was observed in cells grown under glucose limitation at pH 7.0 and high dilution rate, and the lowest concentration (0.12 nmol/mg of protein) was found in cells grown under glucose excess at pH 7.0 and high dilution rate. The other general component of the phosphoenolpyruvate:sugar phosphotransferase system, the protein HPr, was not influenced significantly by varying growth conditions.
PMCID: PMC259313  PMID: 3338847
18.  CcpA Regulates Central Metabolism and Virulence Gene Expression in Streptococcus mutans▿ †  
Journal of Bacteriology  2008;190(7):2340-2349.
CcpA globally regulates transcription in response to carbohydrate availability in many gram-positive bacteria, but its role in Streptococcus mutans remains enigmatic. Using the fructan hydrolase (fruA) gene of S. mutans as a model, we demonstrated that CcpA plays a direct role in carbon catabolite repression (CCR). Subsequently, the expression of 170 genes was shown to be differently expressed (≥2-fold) in glucose-grown wild-type (UA159) and CcpA-deficient (TW1) strains (P ≤ 0.001). However, there were differences in expression of only 96 genes between UA159 and TW1 when cells were cultivated with the poorly repressing substrate galactose. Interestingly, 90 genes were expressed differently in wild-type S. mutans when glucose- and galactose-grown cells were compared, but the expression of 515 genes was altered in the CcpA-deficient strain in a similar comparison. Overall, our results supported the hypothesis that CcpA has a major role in CCR and regulation of gene expression but revealed that in S. mutans there is a substantial CcpA-independent network that regulates gene expression in response to the carbohydrate source. Based on the genetic studies, biochemical and physiological experiments demonstrated that loss of CcpA impacts the ability of S. mutans to transport and grow on selected sugars. Also, the CcpA-deficient strain displayed an enhanced capacity to produce acid from intracellular stores of polysaccharides, could grow faster at pH 5.5, and could acidify the environment more rapidly and to a greater extent than the parental strain. Thus, CcpA directly modulates the pathogenic potential of S. mutans through global control of gene expression.
PMCID: PMC2293215  PMID: 18223086
19.  Enzymes II of the phosphotransferase system do not catalyze sugar transport in the absence of phosphorylation. 
Journal of Bacteriology  1980;141(2):476-484.
In Salmonella typhimurium, glucose, mannose, and fructose are normally transported and phosphorylated by the phosphoenolpyruvate:sugar phosphotransferase system. We have investigated the transport of these sugars and their non-metabolizable analogs in mutant strains lacking the phospho-carrier proteins of the phosphoenolpyruvate:sugar phosphotransferase system, the enzymes I and HPr, to determine whether the sugar-specific, membrane-bound components of the phosphonenolpyruvate: sugar phosphotransferase system, the enzymes II, can catalyze the uptake of these sugars in the absence of phosphorylation. This process does not occur. We have also isolated mutant strains which lack enzyme I and HPr, but have regained the ability to grow on mannose or fructose. These mutants contained elevated levels of mannokinase (fructokinase). In addition, growth on mannose required constitutive synthesis of the galactose permease. When strains were constructed which lacked the galactose permease, they were unable to grow even on high concentrations of mannose, although elevated levels of mannokinase (fructokinase) were present. These results substantiate the conclusion that the enzymes II of the phosphoenolpyruvate:sugar phosphotransferase system are unable to carry out facilitated diffusion.
PMCID: PMC293650  PMID: 6988384
20.  Regulation of Expression of the Fructan Hydrolase Gene of Streptococcus mutans GS-5 by Induction and Carbon Catabolite Repression 
Journal of Bacteriology  1999;181(9):2863-2871.
The polymers of fructose, levan and inulin, as well as sucrose and raffinose, are substrates for the product of the fruA gene of Streptococcus mutans GS-5. The purpose of this study was to characterize the DNA immediately flanking fruA, to explore the regulation of expression of fruA by the carbohydrate source, and to begin to elucidate the molecular basis for differential expression of the gene. Located 3′ to fruA was an open reading frame (ORF) with similarity to β-fructosidases which was cotranscribed with fruA. A transcriptional initiation site, located an appropriate distance from an extended −10-like promoter, was mapped at 165 bp 5′ to the fruA structural gene. By the use of computer algorithms, two overlapping, stable stem-loop sequences with the potential to function as rho-independent terminators were found in the 5′ untranslated region. Catabolite response elements (CREs), which have been shown to govern carbon catabolite repression (CCR) by functioning as negative cis elements in gram-positive bacteria, were located close to the promoter. The levels of production of fruA mRNA and FruA were elevated in cells growing on levan, inulin, or sucrose as the sole carbohydrate source, and repression was observed when cells were grown on readily metabolizable hexoses. Deletion derivatives containing fusions of fruA promoter regions, lacking sequences 5′ or 3′ to the promoter, and a promoterless chloramphenicol acetyltransferase gene were used (i) to demonstrate the functionality of the promoter mapped by primer extension, (ii) to demonstrate that CCR of the fru operon requires the CRE that is located 3′ to the promoter region, and (iii) to provide preliminary evidence that supports the involvement of an antitermination mechanism in fruA induction.
PMCID: PMC93730  PMID: 10217779
21.  Transport of glucose and mannose by a common phosphoenolpyruvate-dependent phosphotransferase system in Streptococcus mutans GS5. 
Infection and Immunity  1984;43(3):1106-1109.
Decryptified cells of Streptococcus mutans GS5 transport glucose, mannose, and fructose by constitutive phosphoenolpyruvate-dependent phosphotransferase systems (PTSs). Although the non-metabolizable glucose analog 2-deoxyglucose is transported by a PTS, alpha-methylglucose is not taken up by strain GS5. The transport of [14C]mannose and [14C]glucose was almost totally blocked by the heterologous sugars, indicating that these substrates may share a common PTS permease. [14C]fructose transport, however, was not inhibited by large excesses of glucose, indicating the existence of a separate fructose PTS. All "tight" glucose PTS- mutant clones studied were also unable to transport mannose, whereas some "leaky" glucose PTS- clones also were leaky for mannose phosphorylation. Fructose transport in most of these mutant strains was unimpaired, indicating that genetic lesions did not involve soluble (cytoplasmic) PTS components.
PMCID: PMC264305  PMID: 6698606
22.  Characteristics and cariogenicity of a fructanase-defective Streptococcus mutants strain. 
Infection and Immunity  1992;60(9):3673-3681.
Polymers of D-fructose produced by a variety of oral bacteria are believed to function as extracellular carbohydrate reserves. Degradation of these polysaccharides in plaque following exhaustion of dietary carbohydrates is thought to contribute to the extent and duration of the acid challenge to the tooth surface and thus to the initiation and progression of dental caries. Streptococcus mutans produces a fructanase, the product of the fruA gene, which is capable of degrading beta(2,6)- and beta(2,1)-linked fructans that are commonly synthesized by dental plaque microorganisms. To evaluate the role of the FruA protein in exopolysaccharide metabolism and to assess the contribution of this enzyme to the pathogenic potential of S. mutans, a fructanase-deficient strain of S. mutans was constructed. Inactivation of a cloned fruA gene was accomplished in Escherichia coli by using a mini-Mu dE transposon, and then an isogenic mutant of S. mutans UA159 was constructed by allelic exchange. Successful inactivation of fruA was confirmed through the use of biochemical assays, Western blotting (immunoblotting) with anti-recombinant FruA antisera, and Southern hybridization. The data indicated that FruA was the only fructan hydrolase produced by S. mutans UA159. Inactivation of fruA had no significant effects on glucosyltransferase or fructosyltransferase activity. In the rat caries model using animals fed a high-sucrose diet and ad libitum, there were no significant differences in the number or severity of smooth surface, sulcal, or root caries elicited by the fruA mutant and the wild-type organism.
PMCID: PMC257376  PMID: 1500176
23.  Improvement of Escherichia coli production strains by modification of the phosphoenolpyruvate:sugar phosphotransferase system 
The application of metabolic engineering in Escherichia coli has resulted in the generation of strains with the capacity to produce metabolites of commercial interest. Biotechnological processes with these engineered strains frequently employ culture media containing glucose as the carbon and energy source. In E. coli, the phosphoenolpyruvate:sugar phosphotransferase system (PTS) transports glucose when this sugar is present at concentrations like those used in production fermentations. This protein system is involved in phosphoenolpyruvate-dependent sugar transport, therefore, its activity has an important impact on carbon flux distribution in the phosphoenolpyruvate and pyruvate nodes. Furthermore, PTS has a very important role in carbon catabolite repression. The properties of PTS impose metabolic and regulatory constraints that can hinder strain productivity. For this reason, PTS has been a target for modification with the purpose of strain improvement. In this review, PTS characteristics most relevant to strain performance and the different strategies of PTS modification for strain improvement are discussed. Functional replacement of PTS by alternative phosphoenolpyruvate-independent uptake and phosphorylation activities has resulted in significant improvements in product yield from glucose and productivity for several classes of metabolites. In addition, inactivation of PTS components has been applied successfully as a strategy to abolish carbon catabolite repression, resulting in E. coli strains that use more efficiently sugar mixtures, such as those obtained from lignocellulosic hydrolysates.
PMCID: PMC1156936  PMID: 15904518
24.  Genetic locus, distant from ptsM, affecting enzyme IIA/IIB function in Escherichia coli K-12. 
Journal of Bacteriology  1980;142(1):120-130.
Most strains of Escherichia coli K-12 are unable to use the enzyme IIA/IIB (enzyme IIMan) complex of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) in anaerobic growth and therefore cannot utilize glucosamine anaerobically. Introduction into these strains of a ptsG mutation, which eliminates activity of the enzyme IIIGlc/IIB' complex of the PTS, resulted in inability to grow anaerobically on glucose and mannose. Derivative strains able to grow anaerobically on glucosamine had mutations at a locus close to man, the gene coding for phosphomannose isomerase, and had higher enzyme IIA/IIB activities during anaerobic growth than did the parental strain. These results establish a locus affecting function of enzyme IIA/IIB that maps distant from ptsM, the probable structural gene for enzyme IIB.
PMCID: PMC293914  PMID: 6989798
25.  Regulation of sugar transport via the multiple sugar metabolism operon of Streptococcus mutans by the phosphoenolpyruvate phosphotransferase system. 
Journal of Bacteriology  1995;177(19):5704-5706.
In this report, we provide evidence that the transport of sugars in Streptococcus mutans via the multiple sugar metabolism system is regulated by the phosphoenolpyruvate phosphotransferase system. A ptsI-defective mutant (DC10), when grown on the multiple sugar metabolism system substrate raffinose, exhibited reduced growth, transport, and glycolytic activity with raffinose relative to the parent strain BM71. Inhibition of [3H]raffinose uptake was also observed in both BM71 and DC10 with increasing concentrations of glucose and the glucose analogs alpha-methyl glucoside and 2-deoxyglucose.
PMCID: PMC177384  PMID: 7559362

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