Phosphoenolpyruvate:carbohydrate phosphotransferase system of bacteria

Null mutations in the SNF3 gene of Saccharomyces cerevisiae cause a different phenotype than do previously isolated missense mutations

Missense mutations in the SNF3 gene of Saccharomyces cerevisiae were previously found to cause defects in both glucose repression and derepression of the SUC2 (invertase) gene. In addition, the growth properties of snf3 mutants suggested that they were defective in uptake of glucose and fructose. We have cloned the SNF3 gene by complementation and demonstrated linkage of the cloned DNA to the chromosomal SNF3 locus. The gene encodes a 3-kilobase poly(A)-containing RNA, which was fivefold more abundant in cells deprived of glucose. The SNF3 gene was disrupted at its chromosomal locus by several methods to create null mutations. Disruption resulted in growth phenotypes consistent with a defect in glucose uptake. Surprisingly, gene disruption did not cause aberrant regulation of SUC2 expression. We discuss possible mechanisms by which abnormal SNF3 gene products encoded by missense alleles could perturb regulatory functions.

Genetic expression of enzyme I activity of the phosphoenolpyruvate:sugar phosphotransferase system in ptsHI deletion strains of Salmonella typhimurium

Mutants expressing a novel enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system, termed enzyme I, were isolated from strains of Salmonella typhimurium which were deleted for the HPr and enzyme I structural genes. The mutations lay in a newly defined gene, termed ptsJ, which mapped on the S. typhimurium chromosome between the ptsHI operon and the cysA gene.

Evidence for regulation of gluconeogenesis by the fructose phosphotransferase system in Salmonella typhimurium

A genetic locus designated fruR, previously mapped to min 3 on the Salmonella typhimurium chromosome, gave rise to constitutive expression of the fructose (fru) regulon and pleiotropically prevented growth on all Krebs cycle intermediates. Regulatory effects of fruR were independent of cyclic AMP and its receptor protein and did not prevent uptake of Krebs cycle intermediates. Instead, the phosphotransferase system appeared to regulate gluconeogenesis by controlling the activities of phosphoenolpyruvate carboxykinase and phosphoenolpyruvate synthase.

Indirect role of adenylate cyclase and cyclic AMP in chemotaxis to phosphotransferase system carbohydrates in Escherichia coli K-12

Most strains of Escherichia coli K-12 lacking the enzyme adenylate cyclase showed normal chemotaxis toward carbohydrates taken up and phosphorylated by the phosphoenolpyruvate-dependent carbohydrate: phosphotransferase system. The normal reaction was observed even in the absence of externally added cyclic adenosine 3',5'-phosphate, provided that the enzyme II chemoreceptors and the flagella were synthesized. In the CA8306 series of strains, however, the cya-854 deletion abolished chemotaxis toward phosphotransferase system carbohydrates even though growth on and transport of these carbohydrates were not affected. This abnormal phenotype was due to the presence of a specific mutation in strain CA8306 which mapped in or close to the crp locus and apparently prevented expression of a hitherto unidentified molecule involved in enzyme II-mediated signal transduction. This molecule is neither a pts protein nor a cyclic adenosine 3',5'-phosphate-binding protein.

II-BGlc, a glucose receptor of the bacterial phosphotransferase system: molecular cloning of ptsG and purification of the receptor from an overproducing strain of Escherichia coli

The bacterial phosphoenolpyruvate:glycose phosphotransferase system (PTS) consists of interacting cytoplasmic and membrane proteins that catalyze the phosphorylation and translocation of sugar substrates across the cell membrane. One PTS protein, II-BGlc, is the membrane receptor specific for glucose and methyl D-glucopyranosides; the protein has been purified to homogeneity from Salmonella typhimurium [Erni, B., Trachsel, H., Postma, P. & Rosenbusch, J. (1982) J. Biol. Chem. 257, 13726-13730]. In the present experiments, the Escherichia coli ptsG locus, which encodes II-BGlc, was isolated from a transducing phage library and subcloned into plasmid vectors. The resulting plasmids complement the following phenotypic defects of ptsG mutants: growth on glucose, uptake and phosphorylation of methyl alpha-D-glucoside, and repression of the utilization of non-PTS sugars by methyl alpha-glucoside. The transformed cells overproduce II-BGlc 4- to 10-fold, and a Mr 43,000 polypeptide was synthesized from the plasmids in an in vitro transcription/translation system. The E. coli and S. typhimurium II-BGlc proteins differ in their physical properties, and a modified, three-step purification procedure was developed for isolating the E. coli protein.

Proline requirement for glucose utilization by Peptostreptococcus anaerobius ATCC 27337

Resting cells of Peptostreptococcus anaerobius maintained under anaerobic conditions were unable to metabolize either glucose or alanine. The addition of proline to the appropriate suspension, however, resulted in the immediate utilization of both compounds. Fermentation of alanine by the cells required that stoichiometric concentrations of proline be present in the medium; and during the oxidation of alanine, proline was simultaneously reduced to the ring cleavage product delta-aminovaleric acid. Although proline was required to initiate glucose transport, stoichiometric amounts of the imino acid were not necessary for glucose fermentation. Proline also stimulated the uptake and concomitant phosphorylation of the nonmetabolizable glucose analog 2-deoxy-D-glucose. The proline requirement for glucose transport by P. anaerobius could be replaced by adding ferricyanide or simply by aerating the cell suspension. The initiation of sugar uptake by proline, ferricyanide, and O2 was attributed to the capacity of these compounds to function as electron acceptors, which permitted reoxidation of the (reduced) intracellular nucleotide pool and the formation (from an endogenous reserve) of the high-energy donor(s) required for the vectorial transport and phosphorylation of sugar.

Energetics of glucose uptake in Salmonella typhimurium

We have studied the energetics of glucose uptake in Salmonella typhimurium. Strain PP418 transports glucose via the phosphoenolpyruvate: glucose phosphotransferase system, while strain PP1705 lacks this system and can only use the galactose permease for glucose uptake. These two strains were cultured anaerobically in glucose-limited chemostats. Both strains produced ethanol and acetate in equimolar amounts but a significant difference was observed in the molar growth yield on glucose (YGlc). It is suggested that this difference is due to a difference in the energetics of the glucose uptake systems in the two strains. Assuming an equal YATP for both strains, we could calculate that uptake of 1 mole of glucose via the galactose permease consumes the equivalent of 0.5 mole of ATP. With the additional assumption that one proton is transported in symport with one glucose molecule, these results imply a stoichiometry of two protons per ATP hydrolysed.

Pel, the protein that permits lambda DNA penetration of Escherichia coli, is encoded by a gene in ptsM and is required for mannose utilization by the phosphotransferase system

Mannose uptake and phosphorylation in Escherichia coli is catalyzed by the phosphoenolpyruvate:glycose phosphotransferase system (PTS). The mannose-specific complex of the PTS, designated IIMan, comprises lipid and two membrane proteins, II-AMan and II-BMan. The proteins are encoded by ptsM, located at approximately equal to 40 minutes on the E. coli chromosome. A different genetic marker, pel, maps with ptsM, and is required for lambda DNA penetration of the cytoplasmic membrane. Earlier studies suggested that both pel function and II-BMan are encoded by the same gene, while a different gene (also in ptsM) encodes II-AMan. In the present studies, a ptsM clone, pCS13, was isolated from an E. coli HindIII gene bank in pBR322 and restored both mannose termentation and pel+ function to ptsM mutants defective in II-BMan. Subclones of pCS13 show that two distinct genes, manY and manZ, encode the pel+ function and the II-BMan protein, respectively; each gene may have its own promoter; whereas the protein encoded by manY (Pel) alone seems sufficient for lambda sensitivity, all three gene products are required for mannose fermentation, transport of the mannose analogue 2-deoxyglucose, and phosphorylation of the latter by cytoplasmic membranes. Thus, Pel is required for function of the IIMan complex. The efficiency of the complex may depend on the ratio of Pel to IIMan.

Three classes of Escherichia coli mutants selected for aerobic expression of fumarate reductase

Fumarate reductase (encoded by frd) and succinate dehydrogenase (encoded by sdh) of Escherichia coli are both known to catalyze the interconversion of fumarate and succinate. Fumarate reductase, however, is not inducible aerobically and therefore cannot participate in the dehydrogenation of succinate. Three classes of suppressor mutants, classified as frd oxygen-resistant [frd(Oxr)], constitutive [frd(Con)], and gene amplification [frd(Amp)] mutants, were selected from an sdh strain as pseudorevertants that regained the partial ability to grow aerobically on succinate. All contained increased aerobic levels of fumarate reductase activity. In frd(Oxr) mutants expression of the operon showed increased resistance to aerobic repression. Under anaerobic conditions expression of the operon became less dependent on the fnr+ gene product, a pleiotropic activator protein for genes encoding anaerobic respiratory enzymes. Exogenous fumarate, however, was still required for full induction, and repression by nitrate was undiminished. Thus, aerobic repression and anaerobic nitrate repression appear to involve separate mechanisms. In frd(Con) mutants expression of the operon became highly resistant to aerobic repression. Under anaerobic conditions expression of the operon no longer required the fnr+ gene product or exogenous fumarate and became immune to nitrate repression. In partial diploids bearing an frd(Oxr) or an frd(Con) allele and phi(frd+-lac) there was no mutual regulatory influence between the two genetic loci. Thus, the frd mutations act in cis and hence are probably in the promoter region. In frd(Amp) mutants the frd locus was amplified without significant alteration in the pattern of regulation.

Transport of trehalose in Salmonella typhimurium

We have studied trehalose uptake in Salmonella typhimurium and the possible involvement of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) in this process. Two transport systems could recognize and transport trehalose, the mannose PTS and the galactose permease. Uptake of trehalose via the latter system required that it be expressed constitutively (due to a galR or galC mutation). Introduction of a ptsM mutation, resulting in a defective IIMan/IIIMan system, in S. typhimurium strains that grew on trehalose abolished growth on trehalose. A ptsG mutation, eliminating IIGlc of the glucose PTS, had no effect. In contrast, a crr mutation that resulted in the absence of IIIGlc of the glucose PTS prevented growth on trehalose. The inability of crr and also cya mutants to grow on trehalose was due to lowered intracellular cyclic AMP synthesis, since addition of extracellular cyclic AMP restored growth. Subsequent trehalose metabolism could be via a trehalose phosphate hydrolase, if trehalose phosphate was formed via the PTS, or trehalase. Trehalose-grown cells contained trehalase activity, but we could not detect phosphoenolpyruvate-dependent phosphorylation of trehalose in toluenized cells.

Null mutations in the SNF3 gene of Saccharomyces cerevisiae cause a different phenotype than do previously isolated missense mutations

Missense mutations in the SNF3 gene of Saccharomyces cerevisiae were previously found to cause defects in both glucose repression and derepression of the SUC2 (invertase) gene. In addition, the growth properties of snf3 mutants suggested that they were defective in uptake of glucose and fructose. We have cloned the SNF3 gene by complementation and demonstrated linkage of the cloned DNA to the chromosomal SNF3 locus. The gene encodes a 3-kilobase poly(A)-containing RNA, which was fivefold more abundant in cells deprived of glucose. The SNF3 gene was disrupted at its chromosomal locus by several methods to create null mutations. Disruption resulted in growth phenotypes consistent with a defect in glucose uptake. Surprisingly, gene disruption did not cause aberrant regulation of SUC2 expression. We discuss possible mechanisms by which abnormal SNF3 gene products encoded by missense alleles could perturb regulatory functions.

Evidence against direct involvement of cyclic GMP or cyclic AMP in bacterial chemotactic signaling

Defects in phosphotransferase chemotaxis in cya and cpd mutants previously cited as evidence of a cyclic GMP or cyclic AMP intermediate in signal transduction were not reproduced in a study of chemotaxis in Escherichia coli and Salmonella typhimurium. In cya mutants, which lack adenylate cyclase, the addition of cyclic AMP was required for synthesis of proteins that were necessary for phosphotransferase transport and chemotaxis. However, the induced cells retained normal phosphotransferase chemotaxis after cyclic AMP was removed. Phosphotransferase chemotaxis was normal in a cpd mutant of S. typhimurium that has elevated levels of cyclic GMP and cyclic AMP. S. typhimurium crr mutants are deficient in enzyme III glucose, which is a component of the glucose transport system, and a regulator of adenylate cyclase. After preincubation with cyclic AMP, the crr mutants were deficient in enzyme II glucose-mediated transport and chemotaxis, but other chemotactic responses were normal. It is concluded that cyclic GMP does not determine the frequency of tumbling and is probably not a component of the transduction pathway. The only known role of cyclic AMP is in the synthesis of some proteins that are subject to catabolite repression.

Regulation of glycerol kinase by enzyme IIIGlc of the phosphoenolpyruvate:carbohydrate phosphotransferase system

Wild-type glycerol kinase of Escherichia coli is inhibited by both nonphosphorylated enzyme IIIGlc of the phosphoenolpyruvate:carbohydrate phosphotransferase system and fructose 1,6-diphosphate. Mutant glycerol kinase, resistant to inhibition by fructose 1,6-diphosphate, was much less sensitive to inhibition by enzyme IIIGlc. The difference between the wild-type and mutant enzymes was even greater when inhibition was measured in the presence of both enzyme IIIGlc and fructose 1,6-diphosphate. The binding of enzyme IIIGlc to glycerol kinase required the presence of the substrate glycerol.

Relationship between pseudo-HPr and the PEP: fructose phosphotransferase system in Salmonella typhimurium and Escherichia coli

We have studied in Salmonella typhimurium and Escherichia coli the properties of pseudo-HPr suppressor mutations. These mutations suppressed the defects in a ptsH mutant which lacks HPr, one of the enzymes of the phosphoenolpyruvate: carbohydrate phosphotransferase system. The suppressor mutation was mapped in S. typhimurium at 3 min, closely linked to leu. The corresponding chromosomal fragment of 1.7 kb from S. typhimurium and E. coli (extending clockwise from ilvH) was cloned. In a maxicell system a protein with an approximate molecular weight of 36,000 was synthesized. Pseudo-HPr suppressor mutations (fruR) and a deletion extending clockwise from leu resulted in the constitutive expression of the fru operon containing the genes for IIFru (fruA), IIIFru (fruB), fructose 1-phosphate kinase (fruK) and pseudo-HPr (fruF). fruR probably codes for a repressor of the fru operon. Tn10 mutagenesis revealed the following order of genes in the fru operon: fruB-(fruK, fruF)-fruA. Pseudo-HPr activity could replace HPr in PEP-dependent phosphorylation of PTS carbohydrates. IIIFru could be phosphorylated both via HPr and pseudo-HPr, since mutants lacking pseudo-HPr activity were still able to phosphorylate fructose in the presence of added HPr. Both the pseudo-HPr suppressor mutations at 3 min and the deletion extending from leu had an additional phenotype. Introduction of these mutations or deletions was always accompanied by disappearance of PEP synthase activity. Complementation of such a mutant with the cloned fragments reversed both phenotypes at the same time. Possibly, the fruR gene product acts as an activator of the gene coding for PEP synthase.

Does secA mediate coupling between secretion and translation in Escherichia coli?

An amber mutation in the secA gene of Escherichia coli causes a pleiotropic decrease in the synthesis of secreted proteins, including maltose-binding protein (MBP) and alkaline phosphatase. Reversal of the inhibition of MBP synthesis in secA(Am) strains by signal sequence mutations in the malE gene has been reported. These results suggest a coupling between secretion and translation which involves an interaction between the signal sequence of nascent polypeptides and a cellular secretion machinery. Further analysis reported here indicated that signal sequence mutations of MBP or alkaline phosphatase did not selectively overcome the inhibition of MBP or alkaline phosphatase synthesis in secA(Am) strains. Rather, at a given time in parallel experiments there was substantial variability among closely isogenic secA(Am) strains in the magnitude of the synthesis block; this variability could account for the earlier results. Further experiments suggested that the inhibition of MBP synthesis in secA(Am) strains was caused by depletion of cyclic AMP, leading to decreased transcription of the malE gene. However, the secretion defects in secA(Am) strains were not affected by cyclic AMP levels. Therefore, we conclude that the reduction in MBP synthesis was a secondary consequence of the primary export defect in the secA(Am) strains.

Active transport in phototrophic bacteria

Phototrophic bacteria utilize light-driven, cyclic electron flow to pump protons out of their cytoplasm, creating an electrochemical proton gradient, ΔμH+, outside acid and positive. These bacteria exchange external protons for internal cations (Na(+), K(+) and Ca(+2)), allowing the cells to maintain a nearly constant internal pH while maintaining the electrical component of ΔμH+. Na(+)/H(+) exchange also establishes an electrochemical Na(+) gradient. Phototrophic bacteria are able to utilize these electrochemical gradients as energy sources for the uptake of a wide variety of metabolites (e.g., sugars, organic acids and amino acids) via metabolite/cation symports.

Effect of endogenous phosphoenolpyruvate potential on fluoride inhibition of glucose uptake by Streptococcus mutans

The fluoride sensitivity of glucose uptake by whole cell suspensions of Streptococcus mutans was studied. Preincubation of the organism with up to 1 mM glucose markedly reduced the fluoride sensitivity of subsequent glucose uptake at pH 7.0 and 5.5. Glucose preincubation was shown to result in the establishment of a stable pool of three-carbon glycolytic intermediates. On the basis of inhibition studies and thin-layer chromatography of cell extracts, we suggest that 3- and 2-phosphoglycerate are the principal constituents of the pool. Increased concentrations of glucose used in preincubation mixtures was associated with increased pool sizes of the glycolytic intermediates and increased fluoride resistance. Transport of 2-deoxy-D-glucose by permeabilized cells was inhibited by fluoride when 2-phoshoglycerate served as the energy source. Increased concentrations of 2-phosphoglycerate were shown to overcome the fluoride inhibition of transport. The data suggest that establishment of a stable pool of glycolytic intermediates that includes 2-phosphoglycerate (or its progenitors) may contribute significantly to the apparent refractoriness of plaque microbes to fluoride in vivo.

Regulation of cyclic AMP synthesis by enzyme IIIGlc of the phosphoenolpyruvate:sugar phosphotransferase system in crp strains of Salmonella typhimurium

We investigated the claim (J. Daniel, J. Bacteriol. 157:940-941, 1984) that nonphosphorylated enzyme IIIGlc of the phosphoenolpyruvate:sugar phosphotransferase system is required for full synthesis of bacterial cyclic AMP (cAMP). In crp strains of Salmonella typhimurium, cAMP synthesis by intact cells was regulated by the phosphorylation state of enzyme IIIGlc. Introduction of either a pstHI deletion mutation or a crr::Tn10 mutation resulted in a low level of cAMP synthesis. In contrast, crp strains containing a leaky pstI mutation exhibited a high level of cAMP synthesis which was inhibited by phosphotransferase system carbohydrates. From these results, we conclude that phosphorylated enzyme IIIGlc rather than nonphosphorylated enzyme IIIGlc is required for full cAMP synthesis.