Isolation, characterization, and nucleotide sequence of the Streptococcus mutans mannitol-phosphate dehydrogenase gene and the mannitol-specific factor III gene of the phosphoenolpyruvate phosphotransferase system

Current Promising Therapeutic Targets for Aspergillosis Treatment

Aspergillosis is a fungal disease caused by different species of Aspergillus. They live in soil,dust and decomposed material. Number of Aspergillus species found till now is about 300 and more are still to be identified. Only few Aspergillus species can cause human disease and the most common species for human infection is Aspergillus fumigatus, which is a ubiquitous airborne saprophytic fungus. Severity of the disease ranges from an allergic response to life-threatening generalized infection. They grow optimally at 37°C and can grow upto 50°C. The fungal conidia are being constantly inhaled by humans and animals everyday normally gets eliminated by innate immune mechanism. Due to increasing number of immunocompromised patients, severe and fatal Aspergillosis cases have augmented. Currently, available antifungal drug for the treatment of Aspergillosis act on these three molecular target are 14 alpha demethylase for Azoles, ergosterol for Polyene and β-1,3-glucan synthase for Echinocandin. These antifungal drug show high resistance problem and toxicity. So, it is high time to develop new drugs for treatment with reduced toxicity and drug resistant problem. Synthesis of essential amino acid is absent in human as they obtain it from their diet but fungi synthesis these amino acid. Thus, enzymes in this pathway acts as novel drug target. This article summarizes promising drug targets presents in different metabolic pathway of Aspergillus genome and discusses their molecular functions in detail. This review also list down the inhibitors of these novel target. We present a comprehensive review that will pave way for discovery and development of novel antifungals against these drug targets for Aspergillosis treatment.

Harnessing Adaptive Evolution to Achieve Superior Mannitol Production by Lactococcus lactis Using Its Native Metabolism

Mannitol can be obtained as a by-product of certain heterolactic lactic acid bacteria, when grown on substrates containing fructose. Lactococcus lactis, a homolactic lactic acid bacterium, normally does not form mannitol but can be persuaded into doing so by expressing certain foreign enzyme activities. In this study, we find that L. lactis has an inherent capacity to form mannitol from glucose. By adaptively evolving L. lactis or derivatives blocked in NAD⁺ regenerating pathways, we manage to accelerate growth on mannitol. When cells of the adapted strains are resuspended in buffer containing glucose, 4-58% of the glucose metabolized is converted into mannitol, in contrast to nonadapted strains. The highest conversion was obtained for a strain lacking all major NAD⁺ regenerating pathways. Mannitol had an inhibitory effect on the conversion, which we speculated was due to the mannitol uptake system. After its inactivation, 60% of the glucose was converted into mannitol by cells suspended in glucose buffer. Using a two-stage setup, where biomass first was accumulated by aerated culturing, followed by a nonaerated phase (static conditions), it was possible to obtain 6.1 g/L mannitol, where 60% of the glucose had been converted into mannitol, which is the highest yield reported for L. lactis.

The mannitol utilization system of the marine bacterium Zobellia galactanivorans

Mannitol is a polyol that occurs in a wide range of living organisms, where it fulfills different physiological roles. In particular, mannitol can account for as much as 20 to 30% of the dry weight of brown algae and is likely to be an important source of carbon for marine heterotrophic bacteria. Zobellia galactanivorans (Flavobacteriia) is a model for the study of pathways involved in the degradation of seaweed carbohydrates. Annotation of its genome revealed the presence of genes potentially involved in mannitol catabolism, and we describe here the biochemical characterization of a recombinant mannitol-2-dehydrogenase (M2DH) and a fructokinase (FK). Among the observations, the M2DH of Z. galactanivorans was active as a monomer, did not require metal ions for catalysis, and featured a narrow substrate specificity. The FK characterized was active on fructose and mannose in the presence of a monocation, preferentially K(+). Furthermore, the genes coding for these two proteins were adjacent in the genome and were located directly downstream of three loci likely to encode an ATP binding cassette (ABC) transporter complex, suggesting organization into an operon. Gene expression analysis supported this hypothesis and showed the induction of these five genes after culture of Z. galactanivorans in the presence of mannitol as the sole source of carbon. This operon for mannitol catabolism was identified in only 6 genomes of Flavobacteriaceae among the 76 publicly available at the time of the analysis. It is not conserved in all Bacteroidetes; some species contain a predicted mannitol permease instead of a putative ABC transporter complex upstream of M2DH and FK ortholog genes.

Molecular cloning and characterization of mannitol-1-phosphate dehydrogenase from Vibrio cholerae

Vibrio cholerae utilizes mannitol through an operon of the phosphoenolpyruvate-dependent phosphotransferase (PTS) type. A gene, mtlD, encoding mannitol-1-phosphate dehydrogenase was identified within the 3.9 kb mannitol operon of V. cholerae. The mtlD gene was cloned from V. cholerae O395, and the recombinant enzyme was functionally expressed in E. coli as a 6×His-tagged protein and purified to homogeneity. The recombinant protein is a monomer with a molecular mass of 42.35 kDa. The purified recombinant MtlD reduced fructose 6-phosphate (F6P) using NADH as a cofactor with a K(m) of 1.54 +/- 0.1 mM and V(max) of 320.8 +/- 7.81 micronmol/min/mg protein. The pH and temperature optima for F6P reduction were determined to be 7.5 and 37°C, respectively. Using quantitative real-time PCR analysis, mtlD was found to be constitutively expressed in V. cholerae, but the expression was up-regulated when grown in the presence of mannitol. The MtlD expression levels were not significantly different between V. cholerae O1 and non-O1 strains.

How phosphotransferase system-related protein phosphorylation regulates carbohydrate metabolism in bacteria

The phosphoenolpyruvate(PEP):carbohydrate phosphotransferase system (PTS) is found only in bacteria, where it catalyzes the transport and phosphorylation of numerous monosaccharides, disaccharides, amino sugars, polyols, and other sugar derivatives. To carry out its catalytic function in sugar transport and phosphorylation, the PTS uses PEP as an energy source and phosphoryl donor. The phosphoryl group of PEP is usually transferred via four distinct proteins (domains) to the transported sugar bound to the respective membrane component(s) (EIIC and EIID) of the PTS. The organization of the PTS as a four-step phosphoryl transfer system, in which all P derivatives exhibit similar energy (phosphorylation occurs at histidyl or cysteyl residues), is surprising, as a single protein (or domain) coupling energy transfer and sugar phosphorylation would be sufficient for PTS function. A possible explanation for the complexity of the PTS was provided by the discovery that the PTS also carries out numerous regulatory functions. Depending on their phosphorylation state, the four proteins (domains) forming the PTS phosphorylation cascade (EI, HPr, EIIA, and EIIB) can phosphorylate or interact with numerous non-PTS proteins and thereby regulate their activity. In addition, in certain bacteria, one of the PTS components (HPr) is phosphorylated by ATP at a seryl residue, which increases the complexity of PTS-mediated regulation. In this review, we try to summarize the known protein phosphorylation-related regulatory functions of the PTS. As we shall see, the PTS regulation network not only controls carbohydrate uptake and metabolism but also interferes with the utilization of nitrogen and phosphorus and the virulence of certain pathogens.

Synthesis of arabinitol 1-phosphate and its use for characterization of arabinitol-phosphate dehydrogenase

D-arabinitol 1-phosphate (Ara-ol1-P), a substrate for D-arabinitol-phosphate dehydrogenase (APDH), was chemically synthesized from D-arabinonic acid in five steps (O-acetylation, chlorination, reduction, phosphorylation, and de-O-acetylation). Ara-ol1-P was used as a substrate for the characterization of APDH from Bacillus halodurans. APDH converts Ara-ol1-P to xylulose 5-phosphate in the oxidative reaction; both NAD(+) and NADP(+) were accepted as co-factors. Kinetic parameters for the oxidative and reductive reactions are consistent with a ternary complex mechanism.

Biochemical and genetic characterization of a novel enzyme of pentitol metabolism: D-arabitol-phosphate dehydrogenase

An enzyme with a specificity that has not been described previously, D-arabitol-phosphate dehydrogenase (APDH), has been purified from cell lysate of Enterococcus avium. SDS/PAGE indicated that the enzyme had a molecular mass of 41+/-2 kDa, whereas a molecular mass of 160+/-5 kDa was observed under non-denaturing conditions, implying that the APDH may exist as a tetramer with identical subunits. Purified APDH was found to have a narrow substrate specificity, converting only D-arabitol 1-phosphate and D-arabitol 5-phosphate into xylulose 5-phosphate and ribulose 5-phosphate, respectively, in the oxidative reaction. Both NAD(+) and NADP(+) were accepted as cofactors. Based on the partial protein sequences, the APDH gene was cloned. Homology comparisons place APDH within the medium-range dehydrogenase family. Unlike most members of this family, APDH requires Mn(2+) but no Zn(2+) for enzymic activity. The DNA sequence surrounding the gene suggests that it belongs to an operon that also contains several components of phosphotransferase system. Both biochemical evidence and protein sequence homology comparisons indicate that similar enzymes are widespread among the Gram-positive bacteria. Their apparent biological role is to participate in arabitol catabolism via the 'arabitol phosphate route', similar to the ribitol and xylitol catabolic routes described previously.

The transcriptional regulation of the Streptococcus mutans bgl regulon

A beta-glucoside utilization regulon recently isolated from Streptococcus mutans has been shown to contain genes involved in beta-glucoside hydrolysis and a putative regulator. The bglP gene encodes a beta-glucoside-specific enzyme II (EII) component of the phosphoenolpyruvate-dependent phosphotransferase system, the bglC gene encodes a putative transcriptional regulator, and the bglA gene encodes a putative phospho-beta-glucosidase. To investigate the transcriptional activity of these genes, the putative promoter regions of the bglP, bglC and bglA genes were fused with the E. coli lacZ reporter gene. The resultant reporter plasmids were used to monitor the transcriptional activity of these loci in S. mutans. The results illustrate that these genes are not repressed by glucose in the presence of an inducing beta-glucoside, esculin, to the levels of expression observed in the absence of esculin. Therefore, these loci are not subject to catabolite repression by glucose to noninduced levels of expression. The bglC gene product was determined to be a positive transcriptional regulator of the bglA gene but does not regulate the expression of the bglP gene. Thus, regulation of these loci requires different and multiple control mechanisms.

Novel phosphotransferase system genes revealed by bacterial genome analysis: the complete complement of pts genes in mycoplasma genitalium

The complete sequence of the Mycoplasma genitalium chromosome has recently been determined. We here report analyses of the genes encoding proteins of the phosphoenolpyruvate:sugar phosphotransferase system, PTS. These genes encode (1) Enzyme I, (2) HPr, (3) a glucose-specific Enzyme IICBA, (4) an inactive glucose-specific Enzyme IIB, lacking the active site cysteyl residue, and (5) a fructose-specific Enzyme IIABC. Some of the unique features of these genes and their enzyme products are as follows. (1) Each of the genes is encoded within a distinct operon. (2) Both Enzyme I and HPr have basic isoelectric points. (3) The glucose-specific Enzyme IIC bears a centrally located, hydrophilic, 200 amino acyl residue insert that lacks sequence similarity with any protein in the current database. (4) The fructose-specific Enzyme II has a domain order (IIABC), different from those of previously characterized fructose permeases, and its IIA domain more closely resembles the IIANtr protein of Escherichia coli than other fructose-specific IIA domains. The potential significance of these novel features is discussed.

The mtl genes and the mannitol-1-phosphate dehydrogenase from Klebsiella pneumoniae KAY2026

The mtl operon of Klebsiella pneumoniae KAY2026 (formerly Aerobacter aerogenes 1033-5P14) was shown to contain as the promoter-proximal gene mtlA, encoding a D-mannitol-specific enzyme II transporter (IICBA(Mtl)). This gene is followed by mtlD, coding for a mannitol-1-phosphate dehydrogenase (MtlD, 382 amino acid residues), and mtlR (MtlR, 195 amino acid residues) coding for a putative repressor, gene mtlR overlaps the termination codon of mtlD. The DNA and protein sequences are highly similar to the corresponding genes (81% identical bp) and proteins (79-85% identical amino acids) of Escherichia coli K-12. A truncated form of MtlD lacking the 162 C-terminal amino acid residues still shows 10% dehydrogenase activity which may explain the controversy in the literature concerning the properties of mannitol-phosphate and other medium-length dehydrogenases.

The mannitol-specific enzyme II (mtlA) gene and the mtlR gene of the PTS of Streptococcus mutans

The phosphoenolpyruvate-dependent phosphotransferase system (PTS) is widely found among Gram-positive bacteria. It is the major source of carbohydrate transport in the dental pathogen Streptococcus mutans. The transported carbohydrates are fermented to produce large amounts of lactic acid which initiates dental caries. The authors have isolated the S. mutans gene for the mannitol-specific Enzyme II (EII) component of the PTS, mtlA, and the adjacent mtlR gene, which is located in the same operon. The mtlR gene is located between mtlA and the genes mtlF and mtlD. The nucleotide sequence of the mtlA and mtlR loci has been determined. The deduced mtlA gene product of S. mutans consists of 589 amino acids with a molecular mass of 62.0 kDa. It exhibits similarity with the mtlA gene products from other organisms. However, the similarity between these proteins is generally restricted to the 470 amino-terminal residues of the S. mutans protein. This region would correspond to the EIICB domains of the PTS. The authors have previously shown that the S. mutans mtlF gene product exhibits 76.6% similarity to the carboxyl-terminal 143 amino acids of the Escherichia coli mtlA product and that the mtlF gene encodes the EIIA domain of the PTS. Thus, the genes that encode the EIICB and the EIIA domains are separated by approximately 2250 bp. In many organisms, all of the EII domains may be fused together to form one molecule. The fact that these domains are separated by this distance in S. mutans supports the hypothesis that various functional domains of the PTS have been rearranged during evolution. The sequence of the 119 carboxyl-terminal amino acids of the S. mutans mtlA gene product also displays homology to the carboxyl-terminal end of the EIIB domain of various mannitol PTSs. Thus, this domain may have been duplicated in S. mutans during evolution of the operon. The mtlR gene is located in the same operon structure as mtlA but these loci are separated by an intragenic space. The precise 5' end of the mtlR locus cannot be determined either by in vitro transcription-translation assays or based upon nucleotide sequence analysis because of the apparent lack of a ribosome-binding site preceding the gene. The deduced mtlR gene product, which consists of approximately 650 amino acids with a molecular mass of 75.3 kDa, exhibits limited similarity to several potential transcriptional regulators. However, the exact function of this locus is currently unknown.

Physical and genetic map of Streptococcus mutans GS-5 and localization of five rRNA operons

The physical map of the 2.1 megabase chromosome of Streptococcus mutans GS-5 has been refined by including all ApaI and SmaI fragments of 5 kbp or greater, and by positioning the fragments generated by the endonuclease I-CeuI. Sixty-three new genetic loci have been added to the map, so that it now contains 90 loci. The new loci include those for 35 cloned streptococcal genes of established function and for 23 S. mutans genes of putative function. In addition, five rrn operons were identified and placed on the map of the chromosome. The presence of a SmaI site in each of the rrn operons allowed the direction of transcription of each operon to be deduced. The orientation of the rrn loci indicates that their transcription is directed away from a small region of the chromosome, identifying a possible region for the initiation of chromosome replication.

The Bacillus stearothermophilus mannitol regulator, MtlR, of the phosphotransferase system. A DNA-binding protein, regulated by HPr and iicbmtl-dependent phosphorylation

D-Mannitol is taken up by Bacillus stearothermophilus and phosphorylated via a phosphoenolpyruvate-dependent phosphotransferase system (PTS). The genes involved in the mannitol uptake were recently cloned and sequenced. One of the genes codes for a putative transcriptional regulator, MtlR. The presence of a DNA binding helix-turn-helix motif and two antiterminator-like PTS regulation domains, suggest that MtlR is a DNA-binding protein, the activity of which can be regulated by phosphorylation by components of the PTS. To demonstrate DNA binding of MtlR to a region upstream of the mannitol promoter, by DNA footprinting, MtlR was overproduced and purified. EI, HPr, IIAmtl, and IICBmtl of B. stearothermophilus were purified and used to demonstrate that MtlR can be phosphorylated and regulated by HPr and IICBmtl, in vitro. Phosphorylation of MtlR by HPr increases the affinity of MtlR for its binding site, whereas phosphorylation by IICBmtl results in a reduction of this affinity. The differential effect of phosphorylation, by two different proteins, on the DNA binding properties of a bacterial transcriptional regulator has not, to our knowledge, been described before. Regulation of MtlR by two components of the PTS is an example of an elegant control system sensing both the presence of mannitol and the need to utilize this substrate.

Cloning and characterization of NADP-mannitol dehydrogenase cDNA from the button mushroom, Agaricus bisporus, and its expression in response to NaCl stress

Mannitol, a six-carbon sugar alcohol, is the main storage carbon in the button mushroom, Agaricus bisporus. Given the physiological importance of mannitol metabolism in growth, fruit body development, and salt tolerance of A. bisporus, the enzyme responsible for mannitol biosynthesis, NADP-dependent mannitol dehydrogenase (MtDH) (EC 1.1.1.138), was purified to homogeneity, and MtDH cDNA was cloned, sequenced, and characterized. To our knowledge, this represents the first report on the isolation of a cDNA encoding an NADP-dependent mannitol dehydrogenase. The MtDH cDNA contains an open reading frame of 789 bp encoding a protein of approximately 28 kDa. The N-terminal and internal amino acid sequences of the deduced protein exactly matched the ones determined from the purified MtDH subunit, whereas the amino acid composition of the deduced protein was nearly identical to that of the purified MtDH. The MtDH cDNA showed high homology with a plant-induced short-chain dehydrogenase from Uromyces fabae. Phylogenetic analysis based on amino acid sequences from mannitol(-1-phosphate) dehydrogenases indicated a close relationship between the substrate specificity of the enzymes and phylogenetic differentiation. Salt-stressed fruit bodies showed an overall increase in mannitol biosynthesis, as was evident from the increase in MtDH activity, MtDH abundance, and MtDH RNA accumulation. Furthermore, the MtDH transcript level seems to be under developmental control, as MtDH RNA accumulated during maturation of the fruit body.

The functional importance of structural differences between the mannitol-specific IIAmannitol and the regulatory IIAnitrogen

The three-dimensional structures of the IIA domain of the mannitol-specific phosphoenol-pyruvate dependent phosphotransferase system (PTS) of Escherichia coli and the regulatory IIAntr enzyme have been compared. The enzymes are 20% identical in sequence and contain the sequence motif specific for IIA proteins belonging to the mannitol-fructose family of the PTS. The fold of the enzymes is nearly identical, which confirms their evolution from a common ancestor. Moreover, the phosphorylation site of IIAmtl (His65) and one of the observed conformations of the active site Arg49 are extremely similar to their equivalents (His73 and Arg57) in IIAntr. In contrast, His120, the equivalent of the second active site His111 of IIAmtl, is not located in the active site of IIAntr but points into the solvent on the other side of the molecule. The different position of His120 makes it unlikely that this residue assists in phosphoryl transfer in the regulatory IIA(ntr)s. As His120 is conserved in all IIAntr enzymes, it could have an essential role in the recognition of the target protein of IIAntr.

Identification of a homolog of CcpA catabolite repressor protein in Streptococcus mutans

A locus containing a gene with homology to ccpA of other bacteria has been cloned from Streptococcus mutans LT11, sequenced, and named regM. Upstream of the regM gene, on the opposite strand, is a gene encoding an X-Pro dipeptidase, pepQ. A 14-bp palindromic sequence with homology to the consensus catabolite-responsive element sequence lay in the promoter region between the two genes. To study the function of regM, the gene was inactivated by insertion of an antibiotic resistance marker. Diauxic growth of S. mutans on a number of sugars in the presence of glucose was not affected by disruption of regM. The loss of RegM increased glucose repression of alpha-galactosidase, mannitol-1-P dehydrogenase, and P-beta-galactosidase activities. These results suggest that while RegM can affect catabolite repression in S. mutans, it does not conform to the model proposed for CcpA in Bacillus subtilis.

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

Streptococcus mutans transports glucose via the phosphoenolpyruvate (PEP)-dependent sugar phosphotransferase system (PTS). Earlier studies indicated that an alternate glucose transport system functions in this organism under conditions of high growth rates, low pH, or excess glucose. To identify this system, S. mutans BM71 was transformed with integration vector pDC-5 to generate a mutant, DC10, defective in the general PTS protein enzyme I (EI). This mutant expressed a defective EI that had been truncated by approximately 150 amino acids at the carboxyl terminus as revealed by Western blot (immunoblot) analysis with anti-EI antibody and Southern hybridizations with a fragment of the wild-type EI gene as a probe. Phosphotransfer assays utilizing 32P-PEP indicated that DC10 was incapable of phosphorylating HPr and EIIAMan, indicating a nonfunctional PTS. This was confirmed by the fact that DC10 was able to ferment glucose but not a variety of other PTS substrates and phosphorylated glucose with ATP and not PEP. Kinetic assays indicated that the non-PTS system exhibited an apparent Ks of 125 microM for glucose and a Vmax of 0.87 nmol mg (dry weight) of cells-1 min-1. Sugar competition experiments with DC10 indicated that the non-PTS transport system had high specificity for glucose since glucose transport was not significantly by a 100-fold molar excess of several competing sugar substrates, including 2-deoxyglucose and alpha-methylglucoside. These results demonstrate that S. mutans possesses a glucose transport system that can function independently of the PEP PTS.

Novel proteins of the phosphotransferase system encoded within the rpoN operon of Escherichia coli. Enzyme IIANtr affects growth on organic nitrogen and the conditional lethality of an erats mutant

Two rpoN-linked delta Tn10-kan insertions suppress the conditionally lethal erats allele. One truncates rpoN while the second disrupts another gene (ptsN) in the rpoN operon and does not affect classical nitrogen regulation. Neither alter expression of era indicating that suppression is post-translational. Plasmid clones of ptsN prevent suppression by either disruption mutation indicating that this gene is important for lethality caused by erats. rpoN and six neighboring genes were sequenced and compared with sequences in the database. Two of these genes encode proteins homologous to Enzyme IIAFru and HPr of the phosphoenolpyruvate:sugar phosphotransferase system. We designate these proteins IIANtr (ptsN) and NPr (npr). Purified IIANtr and NPr exchange phosphate appropriately with Enzyme I, HPr, and Enzyme IIA proteins of the phosphoenolpyruvate: sugar phosphotransferase system. Several sugars and tricarboxylic acid cycle intermediates inhibited growth of the ptsN disruption mutant on medium containing an amino acid or nucleoside base as a combined source of nitrogen, carbon, and energy. This growth inhibition was relieved by supplying the ptsN gene or ammonium salts but was not aleviated by altering levels of exogenously supplied cAMP. These results support our previous proposal of a novel mechanism linking carbon and nitrogen assimilation and relates IIANtr to the unknown process regulated by the essential GTPase Era.

Analysis of a cis-active sequence mediating catabolite repression in gram-positive bacteria

One form of catabolite repression (CR) in the Gram-positive genus, Bacillus, is mediated by a cis-acting element (CRE). We use here a consensus sequence to identify such elements in sequenced genes of Gram-positive bacteria. These are analysed with respect to position and type of gene in which they occur. CRE sequences near the promoter region are mainly identified in genes encoding carbon catabolic enzymes, which are thus likely to be subject to CR by a global mechanism. Functional aspects of CREs are evaluated.

Novel phosphotransferase system genes revealed by bacterial genome analysis: unique, putative fructose- and glucoside-specific systems

Analyses of sequences made available through the Escherichia coli genome project in the 87.2-89.2-min and 81.5-84.5-min regions have revealed 2 putative operons encoding proteins of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). The first putative operon, designated frv, includes 4 open reading frames (ORFs), ORFf147, ORFf485, ORFf356, and ORFf582, ORFf147 and ORFf485 comprise an Enzyme IIA-Enzyme IIBC pair of the PTS. The sequence similarity of ORFf485 to previously characterized fructose-specific Enzymes IIBC suggests that ORFf485 may be specific for fructose. ORFf147 encodes a protein with comparable degrees of sequence similarity to fructose and mannitol-specific Enzymes IIA as well as homologous proteins implicated in sigma 54-dependent transcriptional regulation. Unique features of this system include a detached IIA protein and the absence of a IIB domain duplication. ORFf356 and ORFf582 are functionally unidentified and nonhomologous to other ORFs in the current protein databases, but ORFf582 contains 2 N-terminal helix-turn-helix motifs, suggestive of a role in frv operon transcriptional regulation. The second putative operon, designated glv, includes 3 ORFs, ORFf455, ORFf161, and ORFf212. We suggest that ORFf455 was incorrectly assigned and should be designated ORFf368. ORFf368 and ORFf161 encode an Enzyme IIC and IIB pair of the PTS showing greatest sequence similarity to Enzymes II specific for sugars of the gluco configuration. ORFf212 encodes a protein with sequence similarity to a phospho-beta-glucosidase and an alpha-galactosidase. No putative transcriptional regulator of the glv operon was found. This operon is the first one encoding a putative PTS permease with detached Enzymes IIB and IIC and lacking an Enzyme IIA. It is suggested that both the frv and glv operons are cryptic in E. coli and that additional genes encoding novel PTS-related proteins will be revealed by bacterial genome sequence analyses.

Phosphoenolpyruvate:carbohydrate phosphotransferase systems of bacteria

Numerous gram-negative and gram-positive bacteria take up carbohydrates through the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS). This system transports and phosphorylates carbohydrates at the expense of PEP and is the subject of this review. The PTS consists of two general proteins, enzyme I and HPr, and a number of carbohydrate-specific enzymes, the enzymes II. PTS proteins are phosphoproteins in which the phospho group is attached to either a histidine residue or, in a number of cases, a cysteine residue. After phosphorylation of enzyme I by PEP, the phospho group is transferred to HPr. The enzymes II are required for the transport of the carbohydrates across the membrane and the transfer of the phospho group from phospho-HPr to the carbohydrates. Biochemical, structural, and molecular genetic studies have shown that the various enzymes II have the same basic structure. Each enzyme II consists of domains for specific functions, e.g., binding of the carbohydrate or phosphorylation. Each enzyme II complex can consist of one to four different polypeptides. The enzymes II can be placed into at least four classes on the basis of sequence similarity. The genetics of the PTS is complex, and the expression of PTS proteins is intricately regulated because of the central roles of these proteins in nutrient acquisition. In addition to classical induction-repression mechanisms involving repressor and activator proteins, other types of regulation, such as antitermination, have been observed in some PTSs. Apart from their role in carbohydrate transport, PTS proteins are involved in chemotaxis toward PTS carbohydrates. Furthermore, the IIAGlc protein, part of the glucose-specific PTS, is a central regulatory protein which in its nonphosphorylated form can bind to and inhibit several non-PTS uptake systems and thus prevent entry of inducers. In its phosphorylated form, P-IIAGlc is involved in the activation of adenylate cyclase and thus in the regulation of gene expression. By sensing the presence of PTS carbohydrates in the medium and adjusting the phosphorylation state of IIAGlc, cells can adapt quickly to changing conditions in the environment. In gram-positive bacteria, it has been demonstrated that HPr can be phosphorylated by ATP on a serine residue and this modification may perform a regulatory function.

Two open reading frames adjacent to the Escherichia coli K-12 transketolase (tkt) gene show high similarity to the mannitol phosphotransferase system enzymes from Escherichia coli and various gram-positive bacteria

I have subcloned and sequenced the genes cmtB and cmtA of Escherichia coli K-12 which lie adjacent to the tkt gene on the chromosome. The genes cmtB and cmtA could encode a cytoplasmic protein (EIIA) and an integral-membrane protein (EIIBC), respectively, of the bacterial phospho enol pyruvate-dependent carbohydrate phosphotransferase system. High similarity to the Enzymes IIMtl of Escherichia coli K-12 (gene mtlA) and of Staphylococcus carnosus was detected, but the two genes did not complement mannitol-negative E. coli mutants without the use of a heterologous promoter.

Streptococcus mutans serotype c tagatose 6-phosphate pathway gene cluster

DNA cloned into Escherichia coli K-12 from a serotype c strain of Streptococcus mutans encodes three enzyme activities for galactose utilization via the tagatose 6-phosphate pathway: galactose 6-phosphate isomerase, tagatose 6-phosphate kinase, and tagatose-1,6-bisphosphate aldolase. The genes coding for the tagatose 6-phosphate pathway were located on a 3.28-kb HindIII DNA fragment. Analysis of the tagatose proteins expressed by recombinant plasmids in minicells was used to determine the sizes of the various gene products. Mutagenesis of these plasmids with transposon Tn5 was used to determine the order of the tagatose genes. Tagatose 6-phosphate isomerase appears to be composed of 14- and 19-kDa subunits. The sizes of the kinase and aldolase were found to be 34 and 36 kDa, respectively. These values correspond to those reported previously for the tagatose pathway enzymes in Staphylococcus aureus and Lactococcus lactis.