The Fructose-Specific Phosphotransferase System of Klebsiella pneumoniae Is Regulated by Global Regulator CRP and Linked to Virulence and Growth.

Klebsiella pneumoniae is an opportunistic pathogen, and its hypervirulent variants cause serious invasive community-acquired infections. A genomic view of K. pneumoniae NTUH-2044 for the carbohydrate phosphotransferase system (PTS) found a putative fructose PTS, namely, the Frw PTS gene cluster. The deletion mutant and the complemented mutant of frwC (KP1_1992), which encodes the putative fructose-specific enzyme IIC, were constructed, and the phenotypes were characterized. This transmembrane PTS protein is responsible for fructose utilization. frwC deletion can enhance biofilm formation and capsular polysaccharide (CPS) biosynthesis but decreases the growth rate and lethality in mice. frwC expression was repressed in the cyclic AMP receptor protein (CRP) mutant. Electrophoretic mobility shift assay showed that CRP can directly bind to the promoter of frwC These results indicated that frwC expression is controlled by CRP directly and that such regulation contributes to bacterial growth, CPS synthesis, and the virulence of the Δcrp strain. The findings help elucidate fructose metabolism and the CRP regulatory mechanism in K. pneumoniae.

Glucose induces delocalization of a flagellar biosynthesis protein from the flagellated pole.

To survive in a continuously changing environment, bacteria sense concentration gradients of attractants or repellents, and purposefully migrate until a more favourable habitat is encountered. While glucose is known as the most effective attractant, the flagellar biosynthesis and hence chemotactic motility has been known to be repressed by glucose in some bacteria. To date, the only known regulatory mechanism of the repression of flagellar synthesis by glucose is via downregulation of the cAMP level, as shown in a few members of the family Enterobacteriaceae. Here we show that, in Vibrio vulnificus, the glucose-mediated inhibition of flagellar motility operates by a completely different mechanism. In the presence of glucose, EIIA(Glc) is dephosphorylated and inhibits the polar localization of FapA (flagellar assembly protein A) by sequestering it from the flagellated pole. A loss or delocalization of FapA results in a complete failure of the flagellar biosynthesis and motility. However, when glucose is depleted, EIIA(Glc) is phosphorylated and releases FapA such that free FapA can be localized back to the pole and trigger flagellation. Together, these data provide new insight into a bacterial strategy to reach and stay in the glucose-rich area.

Enhancing human-like collagen accumulation by deleting the major glucose transporter ptsG in recombinant Escherichia coli BL21.

Collagen has been proven to be a valuable biomedical material for many medical applications. Human-like collagen (HLC) is a novel important biomedical material with diverse medical applications. In this work, recombinant Escherichia coli BL21 3.7 ∆ptsG was constructed, the characters of ptsG mutant strain were analyzed, and real-time quantitative polymerase chain reaction (PCR) was applied to investigate the effect of ptsG gene deletion on the transcriptional level of the phosphotransferase system (PTS) genes responsible for glucose transport. The HLC production and cell growth ability were 1.33- and 1.24-fold higher than those of its parent strain in the fermentation medium, respectively, and 1.16- and 1.17-fold in the modified minimal medium individually. The acetate accumulation decreased by 42%-56% compared to its parent strain in the fermentation medium, and 70%-87% in the modified minimal medium. The results of RT-qPCR showed that the transcriptional level of crr, ptsH, ptsI, and blgF in ptsG mutant all decreased dramatically, which inferred a decrease in the glucose uptake rate, but the transcriptional level of FruB and manX increased slightly, which demonstrated the activation of fructose- and mannose-specific transport pathways in the ptsG mutant. This study demonstrates that ptsG deletion is an effective strategy to reduce acetate accumulation and increase biomass and HLC production.

Determinants of interaction specificity of the Bacillus subtilis GlcT antitermination protein: functionality and phosphorylation specificity depend on the arrangement of the regulatory domains.

The control of several catabolic operons in bacteria by transcription antitermination is mediated by RNA-binding proteins that consist of an RNA-binding domain and two reiterated phosphotransferase system regulation domains (PRDs). The Bacillus subtilis GlcT antitermination protein regulates the expression of the ptsG gene, encoding the glucose-specific enzyme II of the phosphotransferase system. In the absence of glucose, GlcT becomes inactivated by enzyme II-dependent phosphorylation at its PRD1, whereas the phosphotransferase HPr phosphorylates PRD2. However, here we demonstrate by NMR analysis and mass spectrometry that HPr also phosphorylates PRD1 in vitro but with low efficiency. Size exclusion chromatography revealed that non-phosphorylated PRD1 forms dimers that dissociate upon phosphorylation. The effect of HPr on PRD1 was also investigated in vivo. For this purpose, we used GlcT variants with altered domain arrangements or domain deletions. Our results demonstrate that HPr can target PRD1 when this domain is placed at the C terminus of the protein. In agreement with the in vitro data, HPr exerts a negative control on PRD1. This work provides the first insights into how specificity is achieved in a regulator that contains duplicated regulatory domains with distinct dimerization properties that are controlled by phosphorylation by different phosphate donors. Moreover, the results suggest that the domain arrangement of the PRD-containing antitermination proteins is under selective pressure to ensure the proper regulatory output, i.e. transcription antitermination of the target genes specifically in the presence of the corresponding sugar.

Characterization of MtfA, a novel regulatory output signal protein of the glucose-phosphotransferase system in Escherichia coli K-12.

The glucose-phosphotransferase system (PTS) in Escherichia coli K-12 is a complex sensory and regulatory system. In addition to its central role in glucose uptake, it informs other global regulatory networks about carbohydrate availability and the physiological status of the cell. The expression of the ptsG gene encoding the glucose-PTS transporter EIICB(Glc) is primarily regulated via the repressor Mlc, whose inactivation is glucose dependent. During transport of glucose and dephosphorylation of EIICB(Glc), Mlc binds to the B domain of the transporter, resulting in derepression of several Mlc-regulated genes. In addition, Mlc can also be inactivated by the cytoplasmic protein MtfA in a direct protein-protein interaction. In this study, we identified the binding site for Mlc in the carboxy-terminal region of MtfA by measuring the effect of mutated MtfAs on ptsG expression. In addition, we demonstrated the ability of MtfA to inactivate an Mlc super-repressor, which cannot be inactivated by EIICB(Glc), by using in vivo titration and gel shift assays. Finally, we characterized the proteolytic activity of purified MtfA by monitoring cleavage of amino 4-nitroanilide substrates and show Mlc's ability to enhance this activity. Based on our findings, we propose a model of MtfA as a glucose-regulated peptidase activated by cytoplasmic Mlc. Its activity may be necessary during the growth of cultures as they enter the stationary phase. This proteolytic activity of MtfA modulated by Mlc constitutes a newly identified PTS output signal that responds to changes in environmental conditions.

Increased glucose utilization in Corynebacterium glutamicum by use of maltose, and its application for the improvement of L-valine productivity.

Corynebacterium glutamicum efficiently utilizes maltose as a substrate. We show here that the presence of maltose increases glucose utilization by raising the expression of ptsG, which encodes the glucose-specific EII permease of the phosphotransferase system. Consequently, the L-valine productivity of a pyruvate dehydrogenase complex-deficient C. glutamicum strain was improved by the presence of maltose.

The mannitol operon repressor MtlR belongs to a new class of transcription regulators in bacteria.

Many bacteria express phosphoenolpyruvate-dependent phosphotransferase systems (PTS). The mannitol-specific PTS catalyze the uptake and phosphorylation of d-mannitol. The uptake system comprises several genes encoded in the single operon. The expression of the mannitol operon is regulated by a proposed transcriptional factor, mannitol operon repressor (MtlR) that was first studied in Escherichia coli. Here we report the first crystal structures of MtlR from Vibrio parahemeolyticus (Vp-MtlR) and its homolog YggD protein from Shigella flexneri (Sf-YggD). MtlR and YggD belong to the same protein family (Pfam05068). Although Vp-MtlR and Sf-YggD share low sequence identity (22%), their overall structures are very similar, representing a novel all alpha-helical fold, and indicate similar function. However, their lack of any known DNA-binding structural motifs and their unfavorable electrostatic properties imply that MtlR/YggD are unlikely to bind a specific DNA operator directly as proposed earlier. This structural observation is further corroborated by in vitro DNA-binding studies of E. coli MtlR (Ec-MtlR), which detected no interaction of Ec-MtlR with the well characterized mannitol operator/promoter region. Therefore, MtlR/YggD belongs to a new class of transcription factors in bacteria that may regulate gene expression indirectly as a part of a larger transcriptional complex.

The Lactobacillus casei ptsHI47T mutation causes overexpression of a LevR-regulated but RpoN-independent operon encoding a mannose class phosphotransferase system.

A proteome analysis of Lactobacillus casei mutants that are affected in carbon catabolite repression revealed that a 15-kDa protein was strongly overproduced in a ptsHI47T mutant. This protein was identified as EIIA of a mannose class phosphotransferase system (PTS). A 7.1-kb DNA fragment containing the EIIA-encoding open reading frame and five other genes was sequenced. The first gene encodes a protein resembling the RpoN (sigma54)-dependent Bacillus subtilis transcription activator LevR. The following pentacistronic operon is oriented in the opposite direction and encodes four proteins with strong similarity to the proteins of the B. subtilis Lev-PTS and one protein of unknown function. The genes present on the 7.1-kb DNA fragment were therefore called levR and levABCDX. The levABCDX operon was induced by fructose and mannose. No "-12, -24" promoter typical of RpoN-dependent genes precedes the L. casei lev operon, and its expression was therefore RpoN independent but required LevR. Phosphorylation of LevR by P approximately His-HPr stimulates its activity, while phosphorylation by P approximately EIIBLev inhibits it. Disruption of the EIIBLev-encoding levB gene therefore led to strong constitutive expression of the lev operon, which was weaker in a strain carrying a ptsI mutation preventing phosphorylation by both P approximately EIIBLev and P approximately His-HPr. Expression of the L. casei lev operon is also subject to P-Ser-HPr-mediated catabolite repression. The observed slow phosphoenolpyruvate- and ATP-dependent phosphorylation of HPrI47T as well as the slow phosphoryl group transfer from the mutant P approximately His-HPr to EIIALev are assumed to be responsible for the elevated expression of the lev operon in the ptsHI47T mutant.

Expression of ptsG encoding the major glucose transporter is regulated by ArcA in Escherichia coli.

Because the phosphoenolpyruvate:sugar phosphotransferase system plays multiple regulatory roles in addition to the phosphorylation-coupled transport of many sugars in bacteria, synthesis of its protein components is regulated in a highly sophisticated way. Thus far, the cAMP receptor protein (CRP) complex and Mlc are known to be the major regulators of ptsHIcrr and ptsG expression in response to the availability of carbon sources. In this report, we performed ligand fishing experiments by using the promoters of ptsHIcrr and ptsG as bait to find out new factors involved in the transcriptional regulation of the phosphoenolpyruvate:sugar phosphotransferase system in Escherichia coli, and we found that the anaerobic regulator ArcA specifically binds to the promoters. Deletion of the arcA gene caused about a 2-fold increase in the ptsG expression, and overexpression of ArcA significantly decreased glucose consumption. In vitro transcription assays showed that phospho-ArcA (ArcA-P) represses ptsG P1 transcription. DNase I footprinting experiments revealed that ArcA-P binds to three sites upstream of the ptsG P1 promoter, two of which overlap the CRP-binding sites, and the ArcA-P binding decreases the CRP binding that is essential for the ptsG P1 transcription. These results suggest that the response regulator ArcA regulates expression of enzyme IICB(Glc) mediating the first step of glucose metabolism in response to the redox conditions of growth in E. coli.

The multifactorial influences of RpoS, Mlc and cAMP on ptsG expression under glucose-limited and anaerobic conditions.

The ptsG gene encodes the high-affinity glucose receptor component of the PEP:glucose phosphotransferase system. PtsG is the major glucose transporter in Escherichia coli under glucose-excess conditions but its regulation under glucose limitation or anaerobiosis is poorly defined. Using a ptsG-lacZ transcriptional fusion, ptsG expression was found to peak with low (micromolar) external glucose levels in glucose-limited chemostats, so PtsG is primed to contribute to glucose scavenging under hunger response conditions. This regulatory pattern was confirmed using methyl- alpha-glucoside transport assays of PtsG-dependent transport. The regulation of ptsG by cAMP contributed to the optimal expression with micromolar glucose but ptsG was actually repressed to levels below that in glucose-excess batch cultures at very slow growth rates and submicromolar glucose concentrations. RpoS contributed to repression of ptsG in slow-growing bacteria but not under glucose-excess conditions. Also, Mlc increasingly contributed to the repression of ptsG at residual glucose concentrations too low to saturate PtsG. A similar pattern of ptsG regulation was observed in anaerobic cultures with either glucose-excess or glucose-limiting situations.

Selective regulation of ptsG expression by Fis. Formation of either activating or repressing nucleoprotein complex in response to glucose.

Transcription of ptsG encoding glucose-specific permease, enzyme IICB(Glc), in Escherichia coli is initiated from two promoters, P1 and P2. ptsG transcription is repressed by Mlc, a glucose-inducible regulator of carbohydrate metabolism. The regulation of ptsG P1 transcription is also under positive control by cyclic AMP receptor protein and cyclic AMP complex (CRP.cAMP) as observed in other Mlc regulon. We report here that Fis, one of the nucleoid-associated proteins, plays a key role in glucose induction of Mlc regulon. ptsG transcription was induced when wild-type cells were grown in the presence of glucose. However, in a fis mutant, the basal level of ptsG transcription was higher but decreased when cells were grown in the presence of glucose, which implies the possibility of regulatory interactions among Fis, Mlc, and CRP.cAMP. Footprinting experiments with various probes and transcription assays revealed that Fis assists both Mlc repression and CRP.cAMP activation of ptsG P1 through the formation of Fis.CRP.Mlc or Fis.CRP nucleoprotein complexes at ptsG P1 promoter depending on the availability of glucose in the growth medium. ptsG P2 transcription was inhibited by Fis and Mlc. Tighter Mlc repression and enhanced CRP.cAMP activation of ptsG P1 by Fis enable cells to regulate Mlc regulon efficiently by selectively controlling the concentration of enzyme IICB(Glc) that modulates Mlc activity.

Widespread N-acetyl-D-glucosamine uptake among pelagic marine bacteria and its ecological implications.

Dissolved free and combined N-acetyl-D-glucosamine (NAG) is among the largest pools of amino sugars in the ocean. NAG is a main structural component in chitin and a substantial constituent of bacterial peptidoglycan and lipopolysaccharides. We studied the distribution and kinetics of NAG uptake by the phosphoenolpyruvate:NAG phosphotransferase systems (PTS) in marine bacterial isolates and natural bacterial assemblages in near-shore waters. Of 78 bacterial isolates examined, 60 took up 3H-NAG, while 18 showed no uptake. No systematic pattern in NAG uptake capability relative to phylogenetic affiliation was found, except that all isolates within Vibrionaceae took up NAG. Among 12 isolates, some showed large differences in the relationship between polymer hydrolysis (measured as chitobiase activity) and uptake of the NAG, the hydrolysis product. Pool turnover time and estimated maximum ambient concentration of dissolved NAG in samples off Scripps Pier (La Jolla, Calif.) were 5.9 +/- 3.0 days (n = 10) and 5.2 +/- 0.9 nM (n = 3), respectively. Carbohydrate competition experiments indicated that glucose, glucosamine, mannose, and fructose were taken up by the same system as NAG. Sensitivity to the antibiotic and NAG structural analog streptozotocin (STZ) was developed into a culture-independent approach, which demonstrated that approximately one-third of bacteria in natural marine assemblages that were synthesizing DNA took up NAG. Isolates possessing a NAG PTS system were found to be predominantly facultative anaerobes. These results suggest the hypothesis that a substantial fraction of bacteria in natural pelagic assemblages are facultative anaerobes. The adaptive value of fermentative metabolism in the pelagic environment is potentially significant, e.g., to bacteria colonizing microenvironments such as marine snow that may experience periodic O2-limitation.

Glycerol-3-phosphate-induced catabolite repression in Escherichia coli.

The formation of glycerol-3-phosphate (G3P) in cells growing on TB causes catabolite repression, as shown by the reduction in malT expression. For this repression to occur, the general proteins of the phosphoenolpyruvate-dependent phosphotransferase system (PTS), in particular EIIA(Glc), as well as the adenylate cyclase and the cyclic AMP-catabolite activator protein system, have to be present. We followed the level of EIIA(Glc) phosphorylation after the addition of glycerol or G3P. In contrast to glucose, which causes a dramatic shift to the dephosphorylated form, glycerol or G3P only slightly increased the amount of dephosphorylated EIIA(Glc). Isopropyl-beta-D-thiogalactopyranoside-induced overexpression of EIIA(Glc) did not prevent repression by G3P, excluding the possibility that G3P-mediated catabolite repression is due to the formation of unphosphorylated EIIA(Glc). A mutant carrying a C-terminally truncated adenylate cyclase was no longer subject to G3P-mediated repression. We conclude that the stimulation of adenylate cyclase by phosphorylated EIIA(Glc) is controlled by G3P and other phosphorylated sugars such as D-glucose-6-phosphate and is the basis for catabolite repression by non-PTS compounds. Further metabolism of these compounds is not necessary for repression. Two-dimensional polyacrylamide gel electrophoresis was used to obtain an overview of proteins that are subject to catabolite repression by glycerol. Some of the prominently repressed proteins were identified by peptide mass fingerprinting. Among these were periplasmic binding proteins (glutamine and oligopeptide binding protein, for example), enzymes of the tricarboxylic acid cycle, aldehyde dehydrogenase, Dps (a stress-induced DNA binding protein), and D-tagatose-1,6-bisphosphate aldolase.

YidC, an assembly site for polytopic Escherichia coli membrane proteins located in immediate proximity to the SecYE translocon and lipids.

Like its mitochondrial homolog Oxa1p, the inner membrane protein YidC of Escherichia coli is involved in the integration of membrane proteins. We have analyzed individual insertion steps of the polytopic E. coli membrane protein MtlA targeted as ribosome-nascent chain complexes to inner membrane vesicles. YidC can accommodate at least the first two transmembrane segments of MtlA at the protein lipid interface and retain them even though the length of the nascent chain would amply allow insertion into membrane lipids. An even longer insertion intermediate of MtlA is described that still has the first transmembrane helix bound to YidC while the third contacts SecE and YidC during integration. Our findings suggest that YidC forms a contiguous integration unit with the SecYE translocon and functions as an assembly site for polytopic membrane proteins mediating the formation of helix bundles prior to their release into the membrane lipids.

"Early" protein synthesis of Lactobacillus delbrueckii ssp. bulgaricus in milk revealed by [35S] methionine labeling and two-dimensional gel electrophoresis.

The proteomes of exponentially growing and stationary cells of Lactobacillus delbrueckii ssp. bulgaricus grown in rich medium (MRS) were separated by two-dimensional polyacrylamide gel electrophoresis (2-DE) and quantified after Coomassie staining. Stationary cells grown in MRS were inoculated in reconstituted skim milk, and "early" protein synthesis during the first 30 min of fermentation in milk was monitored by [35S]methionine labeling and 2-DE. In contrast to exponentially growing or stationary cells, the predominant "early" proteins were small (< 15 kDa) and of low pI (< 5.3). Quantification of the proteome of the "early" lag phase based on 47 "spots" revealed that only three "early" proteins accounted for more than 80% of the total label. They were identified as pI 4.7 and 4.9 isoforms of the heat-stable phosphoryl carrier protein (HPr) with 45.2 and 9.4% of total label, respectively, and an unknown protein called EPr1 ("early" protein 1) with 26.6% of total label. Although an N-terminal sequence of 19 amino acids was obtained, no homologs to EPr1 could be found. De novo synthesis of the 10 and 60 kDa heat shock proteins (GroES and GroEL) was considerably lower (0.04 and 0.9% of total label, respectively), indicating only low levels of stress. Synthesis of triosephosphate isomerase (Tpi) as marker for glycolytic enzymes reached only 0.08% of total label. Our results demonstrate that inoculation in milk, resulting in a change from glucose to lactose as carbon source, imposes only little need for synthesis of stress or glycolytic enzymes, as sufficient proteins are present in the stationary, MRS-grown cells. The high level of expression of the pI 4.7 isoform of HPr suggests a regulatory function of the presumed Ser-46 phosphorylated form of HPr.

Purification of Mlc and analysis of its effects on the pts expression in Escherichia coli.

Products of the pts operon of Escherichia coli have multiple physiological roles such as sugar transport, and the operon is controlled by two promoters, P0 and P1. Expression of the pts P0 promoter that is increased during growth in the presence of glucose is also activated by cAMP receptor protein.cAMP. Based on the existence of a sequence that has a high similarity with the known Mlc binding site in the promoter, the effects of the Mlc protein on the pts P0 promoter expression were studied. In vivo transcription assays using wild type and mlc-negative E. coli strains grown in the presence and absence of glucose indicate that Mlc negatively regulates expression of the P0 promoter, and Mlc-dependent repression is relieved by glucose in the growth medium. In vitro transcription assay using purified recombinant Mlc showed that Mlc repressed transcription from the P0 but did not affect the activity of the P1. DNase I footprinting experiments revealed that a Mlc binding site was located around +1 to +25 of the promoter and that Mlc inhibited the binding of RNA polymerase to the P0 promoter. Cells overexpressing Mlc showed a very slow fermentation rate compared with the wild type when grown in the presence of various phosphoenolpyruvate-carbohydrate phosphotransferase system sugars but few differences in the presence of non-phosphoenolpyruvate-carbohydrate phosphotransferase system sugars except maltose. These results suggest that the pts operon is one of major targets for the negative regulation by Mlc, and thus Mlc regulates the utilization of various sugars as well as glucose in E. coli. The possibility that the inducer of Mlc may not be sugar or its derivative but an unknown factor is proposed to explain the Mlc induction mechanism by various sugars.

Alterations in protein expression caused by the hha mutation in Escherichia coli: influence of growth medium osmolarity.

The Hha protein belongs to a new family of regulators involved in the environmental regulation of virulence factors. The aim of this work was to study the effect of the hha mutation on the overall protein pattern of Escherichia coli cells by two-dimensional polyacrylamide gel electrophoresis. The growth medium osmolarity clearly influenced the effect of the hha mutation. The number of proteins whose expression was altered in hha cells, compared with wild-type cells, was three times larger at a high osmolarity than at a low osmolarity. Among the proteins whose expression was modified by the hha allele, both OmpA and protein IIAGlc of the phosphotransferase system could be identified. As this latter enzyme participates in the regulation of the synthesis of cyclic AMP and hence influences the catabolite repression system, we tested whether the expression of the lacZ gene was also modified in hha mutants. This was the case, suggesting that at least some of the pleiotropic effects of the hha mutation could be caused by its effect on the catabolite repression system.

Regulation of the expression of a gene encoding beta-endoglucanase secreted by Myxococcus xanthus during growth: role of genes involved in developmental regulation.

An endoglucanase, CelA, is secreted by Myxococcus xanthus only during exponential growth. The production of this enzyme is decreased by mutations in 5 different genes (Exc +/- phenotype), three of which correspond to asg genes which regulate the production of an early cell-to-cell signal in development. Transcription of celA is decreased in two of these Exc +/- mutants, whereas a post-transcriptional step is affected in two other Exc- mutants. Thus, asg genes, in addition to regulating the onset of development, also regulate a gene (celA) that is expressed during exponential growth and that is not involved in development.

Cloning, expression, and isolation of the mannitol transport protein from the thermophilic bacterium Bacillus stearothermophilus.

A mannitol phosphotransferase system (PTS) was identified in Bacillus stearothermophilus by in vitro complementation with Escherichia coli EI, HPr, and IIA(Mtl). Degenerate primers based on regions of high amino acid similarity in the E. coli and Staphylococcus carnosus EII(Mt1) were used to develop a digoxigenin-labeled probe by PCR. Using this probe, we isolated three overlapping DNA fragments totaling 7.2 kb which contain the genes mtlA, mtlR, mtlF, and mtlD, encoding the mannitol IICB,a regulator, IIA, and a mannitol-1-phosphate dehydrogenase, respectively. The mtl4 gene consists of 1,413 bp coding for a 471-amino-acid protein with a calculated mass of 50.1 kDa. The amino acid sequence shows high similarity with the sequence of IICB(Mtl) of S. carnosus and the IICB part of the IICBA(Mtl)s of E. coli and B. subtilis. The enzyme could be functionally expressed in E. coli by placing it behind the strong tac promoter. The rate of thermal inactivation at 60 degrees C of B. stearothermophilus HCB(Mt1) expressed in E. coli was two times lower than that of E. coli IICB(Mtl). IICB(Mtl) in B. stearothermophilus is maximally active at 85 degrees C and thus very thermostable. The enzyme was purified on Ni-nitrilotriacetic acid resin to greater than 95% purity after six histidines were fused to the C-terminal part of the transporter.

The N-terminal domain of Escherichia coli enzyme I of the phosphoenolpyruvate/glycose phosphotransferase system: molecular cloning and characterization.

The bacterial phosphoenolpyruvate/glycose phosphotransferase system (PTS) comprises a group of proteins that catalyze the transfer of the phosphoryl group from phosphoenolpyruvate (PEP) to sugars concomitant with their translocation. The first two steps of the phosphotransfer sequence are PEP <--> Enzyme I (EI) <--> HPr (the histidine-containing phosphocarrier protein). We have proposed that many functions of the PTS are regulated by EI, which undergoes a monomer/dimer transition. EI monomer (63.5 kDa) comprises two major domains: a flexible C-terminal domain (EI-C) and a protease-resistant, structurally stable N-terminal domain (EI-N) containing the active site His. Trypsin treatment of Salmonella typhimurium EI yielded EI-N, designated EI-N(t). Homogeneous recombinant Escherichia coli EI-N [i.e., EI-N(r)], has now been prepared in quantity, shows the expected thermodynamic unfolding properties and, similarly to EI-N(t), is phosphorylated by phospho-HPr, but not by PEP. In addition, binding of EI-N(r) to HPr was studied by isothermal titration calorimetry: K/a = 1.4 x 10(5) M(-1) and delta H = +8.8 kcal x mol(-1). Both values are comparable to those for HPr binding to intact EI. Fluorescence anisotropy [dansyl-EI-N(r)] and gel filtration of EI-N(r) show that it does not dimerize. These results emphasize the role of EI-C in dimerization and the regulation of intact EI.