The phosphoenolpyruvate:sugar phosphotransferase system and biofilms in gram-positive bacteria

This review will examine the connection between the bacterial phosphoenolpyruvate:sugar phosphotransferase system and biofilms. We will consider both the primary role of the phosphoenolpyruvate:sugar phosphotransferase system in sugar uptake by biofilm cells and its possible role in regulatory processes in cells growing as biofilms, and in establishment and maintenance of these biofilms.     

Characterization of phosphorylated histidine-containing protein (HPr) of the bacterial phosphoenolpyruvate:sugar phosphotransferase system

The histidine-containing phosphocarrier protein (HPr) of the phosphoenolpyruvate:sugar phosphotransferase system, when phosphorylated, contains a 1-phosphohistidinyl (1-P-histidinyl) residue (His-15). The properties of this 1-P-histidinyl residue were investigated by using phospho-HPr (P-HPr), P-HPr-1, and P-HPr-2. HPr-1 and HPr-2 are deamidated forms of HPr produced by boiling. In addition, HPr-1 produced during frozen storage was investigated. Both pH and temperature dependencies of the rate of hydrolysis of the phosphoryl group of the 1-P-histidinyl residue were investigated. The results show that the 1-P-histidinyl residue in HPr and HPr-1 has significantly different properties from free 1-P-histidine and that these differences are attributable to the active-site residues Glu-66 and Arg-17 and the pK of the imidazole group of the 1-P-histidinyl residue in P-HPr. The 1-P-histidinyl residue in P-HPr and P-HPr-1 shows a greater lability at physiological pH than the free amino acid. A proposal for the active site of P-HPr is made on the basis of these results and the recently obtained tertiary structure. In contrast, the hydrolysis properties of the 1-P-histidinyl residue in P-HPr-2 were similar to those obtained for either free 1-P-histidine or denatured P-HPr. The loss of activity that is associated with boiling HPr was shown to be due to HPr-2 formation as HPr-1 was found to be fully active.     

Metabolite-sensitive, ATP-dependent, protein kinase-catalyzed phosphorylation of HPr, a phosphocarrier protein of the phosphotransferase system in gram-positive bacteria

In this review article we summarize the recent information available concerning important mechanistic and physiological aspects of the protein kinase-mediated phosphorylation of seryl residue-46 in HPr, a phosphocarrier protein of the phosphoenolpyruvate: sugar phosphotransferase system in Gram-positive bacteria. Emphasis is placed upon the information recently obtained in two laboratories through the use of site-specific mutants of the HPr protein. The results show that (i) in contrast to eukaryotic protein kinases, the HPr(ser) kinase recognizes the tertiary structure of HPr rather than a restricted part of the primary sequence of the protein; (ii) like seryl protein kinases of eukaryotes, the HPr(ser) kinase can phosphorylate a threonyl residue, but not a tyrosyl residue when such a residue replaces the regulatory seryl residue in position-46 of the protein; (iii) the regulatory consequences of seryl phosphorylation are due to the introduction of a negative charge at position-46 in the protein rather than the bulky phosphate group; and (iv) PTS protein-HPr interactions influence the conformation of HPr, thereby retarding or stimulating the rate of kinase-catalyzed seryl-46 phosphorylation. The physiological consequences of HPr(ser) phosphorylation in vivo are still a matter of debate.     

Promoter-like mutation affecting HPr and enzyme I of the phosphoenolpyruvate: sugar phosphotransferase system in Salmonella typhimurium

A promoter-like mutation, ptsP160, has been identified which drastically reduces expression of the genes specifying two proteins, HPr and enzyme I, of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) in Salmonella typhimurium. This mutation lies between trzA, a gene specifying susceptibility to 1,2,4-triazole, and ptsH, the structural gene for HPr. It leads to a loss of active transport of those sugars that require the PTS for entry into the cell. Pseudorevertants of strains carrying this promoter-like mutation have additional lesions very closely linked to ptsP160 by transduction analysis and are noninducible for HPr and enzyme I above a basal level. Presumably, strains carrying ptsP160 are defective in the normal induction mechanism for HPr and enzyme I, and the pseudorevertants derived from them result from second-site initiation signals within or near this promoter-like element. The induction of HPr and enzyme I above their noninduced levels apparently is not required for transport of at least one PTS sugar, methyl alpha-d-glucopyranoside, since this sugar is taken up by the pseudorevertants at the same rate as by the wild type. The existence of a promoter-like element governing the coordinate inducibility of both HPr and enzyme I suggests that ptsH and ptsI constitute an operon. Wild-type levels of a sugar-specific PTS protein, factor III, are synthesized in response to the crr(+) gene in both a ptsP160 strain and its pseudorevertants; this suggests that the crr(+) gene has its own promoter distinct from ptsP.     

Synthesis of HPr(Ser-P)(His-P) by enzyme I of the phosphoenolpyruvate: sugar phosphotransferase system of Streptococcus salivarius

HPr is a protein of the bacterial phosphoenolpyruvate:sugar phosphotransferase transport system (PTS). In Gram-positive bacteria, HPr can be phosphorylated on Ser(46) by HPr(Ser) kinase/phosphorylase (HPrK/P) and on His(15) by enzyme I (EI) of the PTS. In vitro studies have shown that phosphorylation on one residue greatly inhibits the second phosphorylation. However, streptococci contain significant amounts of HPr(Ser-P)(His approximately P) during exponential growth, and recent studies suggest that phosphorylation of HPr(Ser-P) by EI is involved in the recycling of HPr(Ser-P)(His approximately P). We report in this paper a study on the phosphorylation of Streptococcus salivarius HPr, HPr(Ser-P), and HPr(S46D) by EI. Our results indicate that (i) the specificity constant (k(cat)/K(m)) of EI for HPr(Ser-P) at pH 7.9 was approximately 5000-fold smaller than that observed for HPr, (ii) no metabolic intermediates were able to stimulate HPr(Ser-P) phosphorylation, (iii) the rate of HPr phosphorylation decreased at pHs below 6.5, while that of HPr(Ser-P) increased and was almost 10-fold higher at pH 6.1 than at pH 7.9, (iv) HPr(S46D), a mutated HPr alleged to mimic HPr(Ser-P), was also phosphorylated more efficiently under acidic conditions, and, lastly, (v) phosphorylation of Bacillus subtilis HPr(Ser-P) by B. subtilis EI was also stimulated at acidic pH. Our results suggest that the high levels of HPr(Ser-P)(His approximately P) in streptococci result from the combination of two factors, a high physiological concentration of HPr(Ser-P) and stimulation of HPr(Ser-P) phosphorylation by EI at acidic pH, an intracellular condition that occurs in response to the acidification of the external medium during growth of the culture.     

The presence of two forms of the phosphocarrier protein HPr of the phosphoenolpyruvate:sugar phosphotransferase system in streptococci.

The protein, HPr, a necessary component of the phosphoenolpyruvate phosphotransferase system (PTS) in bacteria, was purified from Streptococcus salivarius by column chromatography. The purified preparation gave only one band when analyzed by sodium dodecylsulfate gel electrophoresis or by isoelectric focusing in polyacrylamide gel (pI = 4.85). However, electrophoresis in Tris-containing buffers under non-denaturing conditions revealed 2 bands that could be phosphorylated by PEP in the presence of enzyme I of the PTS or by ATP with the HPr kinase. Homogeneous preparations of these 2 forms could be obtained by preparative electrophoresis. Each preparation exhibited only 1 band when analyzed by electrophoresis under non-denaturing conditions, indicating that the doublet observed before preparative electrophoresis was not an electrophoretic artefact. The electrophoretic mobility of each protein was not modified following heat-treatment at 100 degrees C for 20 min or storage at -40 degrees C for several months. Both HPr proteins catalyzed in vitro the PEP-dependent phosphorylation of glucose, but at a rate slightly lower than that observed with a preparation of HPr containing both forms of the protein. Both forms were also able to transfer the phosphate group from PEP to the other specific PTS proteins known in S salivarius. Rabbit polyclonal antibodies directed against each form reacted with both proteins. The presence of the 2 forms of HPr was detected in fresh cellular extracts of S salivarius; however, their intracellular ratio varied according to growth conditions. A doublet was also found in many other streptococcal species tested (S mutans, S sobrinus, S sanguis, S thermophilus, S bovis, S rattus) and also in L lactis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Carbohydrate transporters of the bacterial phosphoenolpyruvate: sugar phosphotransferase system (PTS)

The glucose transporter of Escherichia coli couples translocation with phosphorylation of glucose. The IICB(Glc) subunit spans the membrane eight times. Split, circularly permuted and cyclized forms of IICB(Glc) are described. The split variant was 30 times more active when the two proteins were encoded by a dicistronic mRNA than by two genes. The stability and activity of circularly permuted forms was improved when they were expressed as fusion proteins with alkaline phosphatase. Cyclized IICB(Glc) and IIA(Glc) were produced in vivo by RecA intein-mediated trans-splicing. Purified, cyclized IIA(Glc) and IICB(Glc) had 100% and 30% of wild-type glucose phosphotransferase activity, respectively. Cyclized IIA(Glc) displayed increased stability against temperature and GuHCl-induced unfolding.     

The role of phosphorylation of HPr,a phosphocarrier protein of the phosphotransferase system,in the regulation of carbon metabolism in gram-positive bacteria

HPr of the Gram-positive bacterial phosphotransferase system (PTS) can be phosphorylated by an ATP-dependent protein kinase on a serine residue or by PEP-dependent Enzyme I on a histidyl residue. Both phosphorylation events appear to influence the metabolism of non-PTS carbon sources. Catabolite repression of the gluconate (gnt) operon of B. subtilis appears to be regulated by the former phosphorylation event, while glycerol kinase appears to be regulated by the latter phosphorylation reaction. The extent of our understanding of these processes will be described. © 1993 Wiley-Liss, Inc.     

Physiological studies on regulation of glycerol utilization by the phosphoenolpyruvate:sugar phosphotransferase system in Enterococcus faecalis.

In vitro studies with purified glycerol kinase from Enterococcus faecalis have established that this enzyme is activated by phosphorylation of a histidyl residue in the protein, catalyzed by the phosphoenolpyruvate-dependent phosphotransferase system (PTS), but the physiological significance of this observation is not known. In the present study, the regulation of glycerol uptake was examined in a wild-type strain of E. faecalis as well as in tight and leaky ptsI mutants, altered with respect to their levels of enzyme I of the PTS. Glycerol kinase was shown to be weakly repressible by lactose and strongly repressible by glucose in the wild-type strain. Greatly reduced levels of glycerol kinase activity were also observed in the ptsI mutants. Uptake of glycerol into intact wild-type and mutant cells paralleled the glycerol kinase activities in extracts. Glycerol uptake in the leaky ptsI mutant was hypersensitive to inhibition by low concentrations of 2-deoxyglucose or glucose even though the rates and extent of 2-deoxyglucose uptake were greatly reduced. These observations provide strong support for the involvement of reversible PTS-mediated phosphorylation of glycerol kinase in the regulation of glycerol uptake in response to the presence or absence of a sugar substrate of the PTS in the medium. Glucose and 2-deoxyglucose were shown to elicit rapid efflux of cytoplasmic [14C]lactate derived from [14C]glycerol. This phenomenon was distinct from the inhibition of glycerol uptake and was due to phosphorylation of the incoming sugar by cytoplasmic phosphoenolpyruvate. Lactate appeared to be generated by sequential dephosphorylation and reduction of cytoplasmic phosphoenolpyruvate present in high concentrations in resting cells. The relevance of these findings to regulatory phenomena in other bacteria is discussed.     

Characterization of the 1-phosphohistidinyl residue in the phosphocarrier protein HPr of the phosphoenolpyruvate: sugar phosphotransferase system of Streptococcus faecalis

The phosphocarrier protein HPr of the bacterial phosphoenolpyruvate:sugar phosphotransferase system contains 1-phosphohistidine at residue 15. This residue and the active site residue Arg-17 are conserved in HPrs isolated from both Gram-positive and -negative bacteria. The pH- and temperature-dependent hydrolysis of the 1-phosphohistidinyl residue in P-HPr from Streptococcus faecalis has been investigated. The results show that the hydrolysis properties are very similar to those previously reported for P-HPr from Escherichia coli. It was postulated that the unusual hydrolysis properties were due to the presence of a carboxyl group at the active site, and it is now known that in HPr from Escherichia coli the C-terminal residue Glu-85 is present. The results in this paper suggest that a similar carboxyl group is present at the active site in HPr from Streptococcus faecalis.     

Enzyme I of the phosphoenolpyruvate: sugar phosphotransferase system has two sites of phosphorylation per dimer

Enzyme I of the phosphoenolpyruvate: sugar phosphotransferase system of Escherichia coli has been reported to contain one phosphorylation site per dimer and thus operates by either a half of the sites or a flip-flop mechanism [Misset, O., & Robillard, G. T. (1982) Biochemistry 21, 3136-3142; Hoving, T., ten Hoeve-Duurkens, R., & Robillard, G. T. (1984) Biochemistry 23, 4335-4340]. In this paper, the determination of two phosphorylation sites per dimer of enzyme I was made by using a number of different methods. In some experiments, less than two sites per dimer were found, but a concomitant loss in enzyme I activity was also found. The phosphorylated residue in enzyme I was shown to have the properties expected for a N3-phosphohistidinyl residue.     

Identification of a site in the phosphocarrier protein, HPr, which influences its interactions with sugar permeases of the bacterial phosphotransferase system: kinetic analyses employing site-specific mutants.

The permeases of the Escherichia coli phosphoenolpyruvate:sugar phosphotransferase system (PTS), the sugar-specific enzymes II, are energized by sequential phosphoryl transfer from phosphoenolpyruvate to (i) enzyme I, (ii) the phosphocarrier protein HPr, (iii) the enzyme IIA domains of the permeases, and (iv) the enzyme IIBC domains of the permeases which transport and phosphorylate their sugar substrates. A number of site-specific mutants of HPr were examined by using kinetic approaches. Most of the mutations exerted minimal effects on the kinetic parameters characterizing reactions involving phosphoryl transfer from phospho-HPr to various sugars. However, when the well-conserved aspartyl 69 residue in HPr was changed to a glutamyl residue, the affinities for phospho-HPr of the enzymes II specific for mannitol, N-acetylglucosamine, and beta-glucosides decreased markedly without changing the maximal reaction rates. The same mutation reduced the spontaneous rate of phosphohistidyl HPr hydrolysis but did not appear to alter the rate of phosphoryl transfer from phospho-enzyme I to HPr. When the adjacent glutamyl residue 70 in HPr was changed to a lysyl residue, the Vmax values of the reactions catalyzed by the enzymes II were reduced, but the Km values remained unaltered. Changing this residue to alanine exerted little effect. Site-specific alterations in the C terminus of the beta-glucoside enzyme II which reduced the maximal reaction rate of phosphoryl transfer about 20-fold did not alter the relative kinetic parameters because of the aforementioned mutations in HPr. Published three-dimensional structural analyses of HPr and the complex of HPr with the glucose-specific enzyme IIA (IIAGlc) (homologous to the beta-glucoside and N-acetylglucosamine enzyme IIA domains) have revealed that residues 69 and 70 in HPr are distant from the active phosphorylation site and the IIAGlc binding interface in HPr. The results reported therefore suggest that residues D-69 and E-70 in HPr play important roles in controlling conformational aspects of HPr that influence (i) autophosphohydrolysis, (ii) the interaction of this protein with the sugar permeases of the bacterial phosphotransferase system, and (iii) catalysis of phosphoryl transfer to the IIA domains in these permeases.     

Distribution of the phosphoenolpyruvate:glucose phosphotransferase system in fermentative bacteria.

A number of selected fermentative bacteria were surveyed for the presence of the phosphoenolpyruvate:glucose phosphotransferase system, with particular attention to those organisms which ferment glucose by pathways other than the Embden-Meyerhof-Parnas pathway. The phosphoenolpyruvate:glusoe phosphotransferase system was found in all homofermentative lactic acid bacteria tested that ferment glucose via the Embden-Meyerhof-Parnas pathway, but in none of a group of heterofermentative species of Lactobacillus or Leuconostoc, which ferment glucose via the phosphoketolase pathway. A phosphoenolpyruvate:glucose phosphotransferase system was also absent in Zymomonas mobilis, which ferments glucose via an anaerobic Entner-Doudoroff pathway. It thus appears that the phosphotransferase mode of glucose transport is limited to bacteria with the Embden-Meyerhof-Parnas mode of glucose fermentation.     

Deletion mapping of the genes coding for HPr and enzyme I of the phosphoenolpyruvate: sugar phosphotransferase system in Salmonella typhimurium

Sugars transported by a bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) require two soluble proteins: HPr, a low-molecular-weight phosphate-carrier protein, and enzyme I. The structural genes coding for HPr (ptsH) and Enzyme I (ptsI) are shown to be cotransducible in Salmonella typhimurium. The gene order of this region of the Salmonella chromosome is cysA-trzA-ptsH-ptsI...(crr). A method for the isolation of trzA-pts deletion is described. One class of pts deletions extends through ptsH and into ptsI; a second class includes both ptsH and ptsI and extends into or through the crr gene. The crr gene either codes for or regulates the synthesis of a third PTS protein (factor III) which is sugar-specific. A hypothesis is presented for a mechanism of deletion formation.     

Genetic analysis of succinate utilization in enzyme I mutants of the phosphoenolpyruvate: sugar phosphotransferase system in Escherichia coli.

Studies on the reversion characteristics of Escherichia coli strains carrying various mutations in the pts region have led to the recognition of a mutation, suc-1, with a previously undescribed phenotype. Strains carrying the suc-1 mutation grow normally on most sources of carbon but are unable to utilize succinate effectively. The suc-1 mutation can be separated genetically from the tightly linked ptsI6 mutation. Reversion of suc-1 mutants for growth on succinate yields interesting classes of suppressor mutations.     

Phosphoproteins and the phosphoenolpyruvate:sugar phosphotransferase system of Streptococcus salivarius. Detection of two different ATP-dependent phosphorylations of the phosphocarrier protein HPr

Phosphoproteins which arise from incubation of Streptococcus salivarius ATCC25975 crude extracts with [32P]phosphoenolpyruvate and [gamma-32P]ATP, were separated and detected by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography. These procedures were carried out using the methodology that has been developed to allow for the detection of phosphoproteins containing 1-P-histidinyl and 3-P-histidinyl residues, and also to distinguish between these and phosphoproteins containing acid-stable phosphoamino acids such as phosphoserine, phosphothreonine, and phosphotyrosine. Extracts of cells which had been grown with various sugars as carbon sources were investigated to determine both constitutive and inducible phosphoproteins. No evidence was found for phosphoproteins specifically induced by a sugar, and in particular no evidence was found for any IIIsugar phosphocarrier protein of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). Incubation with [gamma-32P]ATP showed that histidine-containing phosphocarrier protein (HPr) of the PTS could be phosphorylated to give both acid-stable and acid-labile phosphoamino acid residues. The acid-labile ATP-dependent phosphorylation activity was activated by glucose-6-P and appeared to produce a 3-P-histidinyl residue in HPr.     

Genetic dissection of specificity determinants in the interaction of HPr with enzymes II of the bacterial phosphoenolpyruvate:sugar phosphotransferase system in Escherichia coli

The histidine protein (HPr) is the energy-coupling protein of the phosphoenolpyruvate (PEP)-dependent carbohydrate:phosphotransferase system (PTS), which catalyzes sugar transport in many bacteria. In its functions, HPr interacts with a number of evolutionarily unrelated proteins. Mainly, it delivers phosphoryl groups from enzyme I (EI) to the sugar-specific transporters (EIIs). HPr proteins of different bacteria exhibit almost identical structures, and, where known, they use similar surfaces to interact with their target proteins. Here we studied the in vivo effects of the replacement of HPr and EI of Escherichia coli with the homologous proteins from Bacillus subtilis, a gram-positive bacterium. This replacement resulted in severe growth defects on PTS sugars, suggesting that HPr of B. subtilis cannot efficiently phosphorylate the EIIs of E. coli. In contrast, activation of the E. coli BglG regulatory protein by HPr-catalyzed phosphorylation works well with the B. subtilis HPr protein. Random mutations were introduced into B. subtilis HPr, and a screen for improved growth on PTS sugars yielded amino acid changes in positions 12, 16, 17, 20, 24, 27, 47, and 51, located in the interaction surface of HPr. Most of the changes restore intermolecular hydrophobic interactions and salt bridges normally formed by the corresponding residues in E. coli HPr. The residues present at the targeted positions differ between HPrs of gram-positive and -negative bacteria, but within each group they are highly conserved. Therefore, they may constitute a signature motif that determines the specificity of HPr for either gram-negative or -positive EIIs.