The Corynebacterium glutamicum aecD gene encodes a C-S lyase with alpha, beta-elimination activity that degrades aminoethylcysteine

Regulation of oxidative stress response and antioxidant modification in Corynebacterium glutamicum

As an efficient and safe industrial bacterium, Corynebacterium glutamicum has extensive application in amino acid production. However, it often faces oxidative stress induced by reactive oxygen species (ROS), leading to diminished production efficiency. To enhance the robustness of C. glutamicum, numerous studies have focused on elucidating its regulatory mechanisms under various stress conditions such as heat, acid, and sulfur stress. However, a comprehensive review of its defense mechanisms against oxidative stress is needed. This review offers an in-depth overview of the mechanisms C. glutamicum employs to manage oxidative stress. It covers both enzymatic and non-enzymatic systems, including antioxidant enzymes, regulatory protein families, sigma factors involved in transcription, and physiological redox reduction pathways. This review provides insights for advancing research on the antioxidant mechanisms of C. glutamicum and sheds light on its potential applications in industrial production.

Challenges and Advances in the Bioproduction of L-Cysteine

L-cysteine is a proteogenic amino acid with many applications in the pharmaceutical, food, animal feed, and cosmetic industries. Due to safety and environmental issues in extracting L-cysteine from animal hair and feathers, the fermentative production of L-cysteine offers an attractive alternative using renewable feedstocks. Strategies to improve microbial production hosts like Pantoea ananatis, Corynebacterium glutamicum, Pseudomonas sp., and Escherichia coli are summarized. Concerning the metabolic engineering strategies, the overexpression of feedback inhibition-insensitive L-serine O-acetyltransferase and weakening the degradation of L-cysteine through the removal of L-cysteine desulfhydrases are crucial adjustments. The overexpression of L-cysteine exporters is vital to overcome the toxicity caused by intracellular accumulating L-cysteine. In addition, we compiled the process engineering aspects for the bioproduction of L-cysteine. Utilizing the energy-efficient sulfur assimilation pathway via thiosulfate, fermenting cheap carbon sources, designing scalable, fed-batch processes with individual feedings of carbon and sulfur sources, and implementing efficient purification techniques are essential for the fermentative production of L-cysteine on an industrial scale.

Toxicomicrobiomics: The Human Microbiome vs. Pharmaceutical, Dietary, and Environmental Xenobiotics

The harmful impact of xenobiotics on the environment and human health is being more widely recognized; yet, inter- and intraindividual genetic variations among humans modulate the extent of harm, mostly through modulating the outcome of xenobiotic metabolism and detoxification. As the Human Genome Project revealed that host genetic, epigenetic, and regulatory variations could not sufficiently explain the complexity of interindividual variability in xenobiotics metabolism, its sequel, the Human Microbiome Project, is investigating how this variability may be influenced by human-associated microbial communities. Xenobiotic-microbiome relationships are mutual and dynamic. Not only does the human microbiome have a direct metabolizing potential on xenobiotics, but it can also influence the expression of the host metabolizing genes and the activity of host enzymes. On the other hand, xenobiotics may alter the microbiome composition, leading to a state of dysbiosis, which is linked to multiple diseases and adverse health outcomes, including increased toxicity of some xenobiotics. Toxicomicrobiomics studies these mutual influences between the ever-changing microbiome cloud and xenobiotics of various origins, with emphasis on their fate and toxicity, as well the various classes of microbial xenobiotic-modifying enzymes. This review article discusses classic and recent findings in toxicomicrobiomics, with examples of interactions between gut, skin, urogenital, and oral microbiomes with pharmaceutical, food-derived, and environmental xenobiotics. The current state and future prospects of toxicomicrobiomic research are discussed, and the tools and strategies for performing such studies are thoroughly and critically compared.

Efficient production of glutathione with multi-pathway engineering in Corynebacterium glutamicum

Glutathione is a bioactive tripeptide composed of glycine, L-cysteine, and L-glutamate, and has been widely used in pharmaceutical, food, and healthy products. The current metabolic studies of glutathione were mainly focused on the native producing strains with precursor amino acid supplementation. In the present work, Corynebacterium glutamicum, a workhorse for industrial production of a series of amino acids, was engineered to produce glutathione. First, the introduction of glutathione synthetase gene gshF from Streptococcus agalactiae fulfilled the ability of glutathione production in C. glutamicum and revealed that L-cysteine was the limiting factor. Then, considering the inherent capability of L-glutamate synthesis and the availability of external addition of low-cost glycine, L-cysteine biosynthesis was enhanced using a varieties of pathway engineering methods, such as disrupting the degradation pathways of L-cysteine and L-serine, and removing the repressor responsible for sulfur metabolism. Finally, the simultaneously introduction of gshF and enhancement of cysteine formation enabled C. glutamicum strain to produce glutathione greatly. Without external addition of L-cysteine and L-glutamate, 756 mg/L glutathione was produced. This is first time to demonstrate the potential of the glutathione non-producing strain C. glutamicum for glutathione production and provide a novel strategy to construct glutathione-producing strains.

Chemical transformation of xenobiotics by the human gut microbiota

The human gut microbiota makes key contributions to the metabolism of ingested compounds (xenobiotics), transforming hundreds of dietary components, industrial chemicals, and pharmaceuticals into metabolites with altered activities, toxicities, and lifetimes within the body. The chemistry of gut microbial xenobiotic metabolism is often distinct from that of host enzymes. Despite their important consequences for human biology, the gut microbes, genes, and enzymes involved in xenobiotic metabolism are poorly understood. Linking these microbial transformations to enzymes and elucidating their biological effects is undoubtedly challenging. However, recent studies demonstrate that integrating traditional and emerging technologies can enable progress toward this goal. Ultimately, a molecular understanding of gut microbial xenobiotic metabolism will guide personalized medicine and nutrition, inform toxicology risk assessment, and improve drug discovery and development.

The cmaR gene of Corynebacterium ammoniagenes performs a novel regulatory role in the metabolism of sulfur-containing amino acids

A novel regulatory gene, which performs an essential function in sulfur metabolism, has been identified inCorynebacterium ammoniagenesand was designatedcmaR(cysteine andmethionine regulator inC.ammoniagenes). ThecmaR-disrupted strain (ΔcmaR) lost the ability to grow on minimal medium, and was identified as a methionine and cysteine double auxotroph. The mutant strain proved unable to convert cysteine to methionine (and vice versa), and lost the ability to assimilate and reduce sulfate to sulfide. In the ΔcmaRstrain, the mRNAs of the methionine biosynthetic genesmetYX,metBandmetFEwere significantly reduced, and the activities of the methionine biosynthetic enzymes cystathionineγ-synthase,O-acetylhomoserine sulfhydrylase, and cystathionineβ-lyase were relatively low, thereby suggesting that thecmaRgene exerts a positive regulatory effect on methionine biosynthetic genes. In addition, with the exception ofcysK, reduced transcription levels of the sulfur-assimilatory genescysIXYZandcysHDNwere noted in thecmaR-disrupted strain, which suggests that sulfur assimilation is also under the positive control of thecmaRgene. Furthermore, the expression of thecmaRgene itself was strongly induced via the addition of cysteine or methionine alone, but not the introduction of both amino acids together to the growth medium. In addition, the expression of thecmaRgene was enhanced in anmcbR-disrupted strain, which suggests thatcmaRis under the negative control of McbR, which has been identified as a global regulator of sulfur metabolism. DNA binding of the purified CmaR protein to the promoter region of its target genes could be demonstratedin vitro. No metabolite effector was required for the protein to bind DNA. These results demonstrated that thecmaRgene ofC. ammoniagenesplays a role similar to but distinct from that of the functional homologuecysRofCorynebacterium glutamicum.

Characteristics of methionine production by an engineered Corynebacterium glutamicum strain

A methionine-producing strain was derived from a lysine-producing Corynebacterium glutamicum through a process of genetic manipulation in order to assess its potential to synthesize and accumulate methionine during growth. The strain carries a deregulated hom gene (hom(FBR)) to abolish feedback inhibition of homoserine dehydrogenase by threonine and a deletion of the thrB gene (delta thrB) to abolish threonine synthesis. The constructed C. glutamicum MH20-22B/hom(FBR)/delta thrB strain accumulated 2.9 g/l of methionine by batch fermentation and showed resistance to methionine analogue ethionine at concentrations up to 30 mM. The growth of the strain was apparently impaired as a result of the accumulation of methionine biosynthetic intermediate, homocysteine. Production assays also revealed that the accumulation of methionine in the growth medium was transient and declined as the carbon source was depleted. During the period of methionine disappearance, the methionine biosynthetic genes were completely repressed in the engineered strains but not in the parental strain. After all, we have not only successfully constructed a methionine-producing C. glutamicum strain by genetic manipulation, but also revealed cellular constraints in attaining high yield and productivity.

Metabolic pathways and biotechnological production of l-cysteine

L-Cysteine is an important amino acid both biologically and commercially. Although most amino acids are commercially produced by fermentation, cysteine is mainly produced by protein hydrolysis. However, synthetic or biotechnological products have been preferred in the market. Biotechnological processes for cysteine production, both enzymatic and fermentative processes, are discussed. Enzymatic process, the asymmetric hydrolysis of DL-2-amino-Delta(2)-thiazoline-4-carboxylic acid to L-cysteine, has been developed and industrialized. The L-cysteine biosynthetic pathways of Escherichia coli and Corynebacterium glutamicum, which are used in many amino acid production processes, are also described. These two bacteria have basically same L-cysteine biosynthetic pathways. L-Cysteine-degrading enzymes and L-cysteine-exporting proteins both in E. coli and C. glutamicum are also described. In conclusion, for the effective fermentative production of L-cysteine directly from glucose, the combination of enhancing biosynthetic activity, weakening the degradation pathway, and exploiting the export system seems to be effective.

The transcriptional regulator SsuR activates expression of the Corynebacterium glutamicum sulphonate utilization genes in the absence of sulphate

In a recent study, the putative regulatory gene cg0012 was shown to belong to the regulon of McbR, a global transcriptional regulator of sulphur metabolism in Corynebacterium glutamicum ATCC 13032. A deletion of cg0012, now designated ssuR (sulphonate sulphur utilization regulator), led to the mutant strain C. glutamicum DK100, which was shown to be blocked in the utilization of sulphonates as sulphur sources. According to DNA microarray hybridizations, transcription of the ssu and seu genes, encoding the sulphonate utilization system of C. glutamicum, was considerably decreased in C. glutamicum DK100 when compared with the wild-type strain. Electrophoretic mobility shift assays with purified SsuR protein demonstrated that the upstream regions of ssuI, seuABC, ssuD2 and ssuD1CBA contain SsuR binding sites. A nucleotide sequence alignment of the four DNA fragments containing the SsuR binding sites revealed a common 21 bp motif consisting of T-, GC- and A-rich domains. Mapping of the transcriptional start sites in front of ssuI, seuABC, ssuD2 and ssuD1CBA indicated that the SsuR binding sites are located directly upstream of identified promoter sequences and that the ssu genes are expressed by leaderless transcripts. Binding of the SsuR protein to its operator was shown to be diminished in vitro by the effector substance sulphate and its direct assimilation products adenosine 5'-phosphosulphate, sulphite and sulphide. Real-time reverse transcription polymerase chain reaction experiments verified that the expression of the ssu and seu genes was also repressed in vivo by the presence of sulphate or sulphite. Therefore, the regulatory protein SsuR activates the expression of the ssu and seu genes in C. glutamicum in the absence of the preferred sulphur source sulphate.

Functional analysis of all aminotransferase proteins inferred from the genome sequence of Corynebacterium glutamicum

Twenty putative aminotransferase (AT) proteins of Corynebacterium glutamicum, or rather pyridoxal-5'-phosphate (PLP)-dependent enzymes, were isolated and assayed among others with L-glutamate, L-aspartate, and L-alanine as amino donors and a number of 2-oxo-acids as amino acceptors. One outstanding AT identified is AlaT, which has a broad amino donor specificity utilizing (in the order of preference) L-glutamate > 2-aminobutyrate > L-aspartate with pyruvate as acceptor. Another AT is AvtA, which utilizes L-alanine to aminate 2-oxo-isovalerate, the L-valine precursor, and 2-oxo-butyrate. A second AT active with the L-valine precursor and that of the other two branched-chain amino acids, too, is IlvE, and both enzyme activities overlap partially in vivo, as demonstrated by the analysis of deletion mutants. Also identified was AroT, the aromatic AT, and this and IlvE were shown to have comparable activities with phenylpyruvate, thus demonstrating the relevance of both ATs for L-phenylalanine synthesis. We also assessed the activity of two PLP-containing cysteine desulfurases, supplying a persulfide intermediate. One of them is SufS, which assists in the sulfur transfer pathway for the Fe-S cluster assembly. Together with the identification of further ATs and the additional analysis of deletion mutants, this results in an overview of the ATs within an organism that may not have been achieved thus far.

The McbR repressor modulated by the effector substance S-adenosylhomocysteine controls directly the transcription of a regulon involved in sulphur metabolism of Corynebacterium glutamicum ATCC 13032

In a recent proteomics study we have shown that the mcbR gene of Corynebacterium glutamicum ATCC 13032 most probably encodes a transcriptional repressor of the TetR type, which regulates the expression of at least six genes involved in the synthesis of sulphur-containing amino acids. By means of DNA microarray hybridizations we detected 86 genes with enhanced transcription in an mcbR mutant when compared with the wild-type strain. Bioinformatic analysis identified the inverted repeat 5'-TAGAC-N6-GTCTA-3' as a consensus sequence within the upstream region of 22 genes and operons, suggesting that the transcription of at least 45 genes is directly controlled by the McbR repressor. These 45 genes encode a variety of functions in (S-adenosyl)methionine and cysteine biosynthesis, in sulphate reduction, in uptake and utilization of sulphur-containing compounds and in transcriptional regulation. The function of the inverted repeat motif as potential McbR binding site in front of the genes hom, cysI, cysK, metK and mcbR was verified experimentally by competitive electrophoretic mobility shift analysis. A systematic search for the potential effector substance modulating the function of McbR revealed that only S-adenosylhomocysteine prevented the binding of McbR to its target sequence. These results indicate that the transcriptional repressor McbR directly regulates a set of genes comprising all aspects of transport and metabolism of the macroelement sulphur in C. glutamicum. As the activity of McbR is modulated by S-adenosylhomocysteine, a major product of transmethylation reactions, the results point also to a novel regulatory mechanism in bacteria to control the biosynthesis of S-adenosylmethionine.

Cometabolism of a nongrowth substrate: L-serine utilization by Corynebacterium glutamicum

Despite its key position in central metabolism, L-serine does not support the growth of Corynebacterium glutamicum. Nevertheless, during growth on glucose, L-serine is consumed at rates up to 19.4 +/- 4.0 nmol min(-1) (mg [dry weight])(-1), resulting in the complete consumption of 100 mM L-serine in the presence of 100 mM glucose and an increased growth yield of about 20%. Use of 13C-labeled L-serine and analysis of cellularly derived metabolites by nuclear magnetic resonance spectroscopy revealed that the carbon skeleton of L-serine is mainly converted to pyruvate-derived metabolites such as L-alanine. The sdaA gene was identified in the genome of C. glutamicum, and overexpression of sdaA resulted in (i) functional L-serine dehydratase (L-SerDH) activity, and therefore conversion of L-serine to pyruvate, and (ii) growth of the recombinant strain on L-serine as the single substrate. In contrast, deletion of sdaA decreased the L-serine cometabolism rate with glucose by 47% but still resulted in degradation of L-serine to pyruvate. Cystathionine beta-lyase was additionally found to convert L-serine to pyruvate, and the respective metC gene was induced 2.4-fold under high internal L-serine concentrations. Upon sdaA overexpression, the growth rate on glucose is reduced 36% from that of the wild type, illustrating that even with glucose as a single substrate, intracellular L-serine conversion to pyruvate might occur, although probably the weak affinity of L-SerDH (apparent Km, 11 mM) prevents substantial L-serine degradation.

The complete Corynebacterium glutamicum ATCC 13032 genome sequence and its impact on the production of L-aspartate-derived amino acids and vitamins

The complete genomic sequence of Corynebacterium glutamicum ATCC 13032, well-known in industry for the production of amino acids, e.g. of L-glutamate and L-lysine was determined. The C. glutamicum genome was found to consist of a single circular chromosome comprising 3282708 base pairs. Several DNA regions of unusual composition were identified that were potentially acquired by horizontal gene transfer, e.g. a segment of DNA from C. diphtheriae and a prophage-containing region. After automated and manual annotation, 3002 protein-coding genes have been identified, and to 2489 of these, functions were assigned by homologies to known proteins. These analyses confirm the taxonomic position of C. glutamicum as related to Mycobacteria and show a broad metabolic diversity as expected for a bacterium living in the soil. As an example for biotechnological application the complete genome sequence was used to reconstruct the metabolic flow of carbon into a number of industrially important products derived from the amino acid L-aspartate.

Genome-wide analysis of the L-methionine biosynthetic pathway in Corynebacterium glutamicum by targeted gene deletion and homologous complementation

The genome sequence of Corynebacterium glutamicum, a gram-positive soil bacterium widely used as an amino acid producer, was analyzed by a similarity-based approach to elucidate the pathway for the biosynthesis of L-methionine. The functions of candidate ORFs were derived by gene deletion and, if necessary, by homologous complementation of suitable mutants. Of nine candidate ORFs (four of which were known previously), seven ORFs (cg0754 (metX), cg0755 (metY), cg1290 (metE), cg1702 (metH), cg2383 (metF), cg2536 (aecD), and cg2687 (metB)) were demonstrated to be part of the pathway while two others (cg0961 and cg3086) could be excluded. C. glutamicum synthesizes methionine in three, respectively four steps, starting from homoserine. C. glutamicum possesses two genes with similarity to homoserine acetyltransferases but only MetX can act as such while Cg0961 catalyzes a different, unknown reaction. For the incorporation of the sulfur moiety, the known functions of MetY and MetB could be confirmed and AecD was proven to be the only functional cystathionine beta-lyase in C. glutamicum, while Cg3086 can act neither as cystathionine gamma-synthase nor as cystathionine beta-lyase. Finally, MetE and MetH, which catalyze the conversion of L-homocysteine to L-methionine, could be newly identified, together with MetF which provides the necessary N(5)-methyltetrahydrofolate.

Genome-based analysis of biosynthetic aminotransferase genes of Corynebacterium glutamicum

Due to broad and overlapping substrate specificities, aminotransferases remain the last uncharacterized enzymes from most amino acid biosynthetic pathways in Corynebacterium glutamicum. We report here a complete description of all aminotransferases participating in the biosynthesis of the branched-chain amino acids and phenylalanine in C. glutamicum. We used methods of profile analysis on the newly available genome sequence to systematically search for and characterize members of the four known aminotransferase classes. This led to the discovery of sixteen new, potential aminotransferase encoding genes in the C. glutamicum genome, eleven of which were subsequently characterized experimentally with respect to their participation in different amino acid biosynthetic pathways. Disruption by insertion mutagenesis of ilvE, encoding a branched-chain amino acid aminotransferase, confirmed its function in leucine and isoleucine biosynthesis. Two double mutants lacking both ilvE and genes classified as class I aminotransferases exhibited additional auxotrophic requirements for valine and phenylalanine, respectively. In C. glutamicum the branched-chain amino acid aminotransferase thus participates in four amino acid biosynthetic pathways, for which in case of valine and phenylalanine biosynthesis two additional enzymes with overlapping substrate specificity exist. The novel protein with aminotransferase activity in valine biosynthesis belongs to the very recently described MocR subfamily of GntR-type helix-turn-helix transcriptional regulators, is located upstream of a potential operon of a newly described pyridoxine biosynthetic pathway and when disrupted, gives rise to a pyridoxine auxotrophy. The theoretical and experimental data we present should further provide a solid platform for ongoing research and understanding of the network of aminotransferases which participate in amino acid biosynthesis in C. glutamicum.

The putative transcriptional repressor McbR, member of the TetR-family, is involved in the regulation of the metabolic network directing the synthesis of sulfur containing amino acids in Corynebacterium glutamicum

In order to isolate transcriptional regulatory proteins involved in L-methionine-dependent repression in Corynebacterium glutamicum, proteins binding to the putative promoter region upstream of the metY gene were isolated by DNA affinity chromatography. One of the isolated proteins was identified as a putative transcriptional repressor of the TetR-family by a mass spectrometry fingerprint technique based on the complete C. glutamicum genome sequence. The respective gene, designated mcbR, was deleted in the mutant strain C. glutamicum DR1. Using 2D-PAGE, the protein contents of the C. glutamicum wild type and the mutant strain DR1 grown in media with or without L-methionine supplementation were compared and a set of six proteins was identified. Their abundance was drastically enhanced in the mutant strain and no longer influenced by L-methionine added to the growth medium. The corresponding genes were identified by mass spectrometry fingerprint analysis. They included metY encoding O-acetyl-L-homoserine sulfhydrylase, metK encoding S-adenosyl-methionine synthethase, hom encoding homoserine dehydrogenase, cysK encoding L-cysteine synthase, cysI encoding an NADPH dependant sulfite reductase, and ssuD encoding an alkanesulfonate monooxygenase. Evidently, the putative transcriptional repressor McbR is involved in the regulation of the metabolic network directing the synthesis of L-methionine in C. glutamicum. The C. glutamicum mcbR mutant can be considered to represent a first step in the construction of an L-methionine production strain.

Purification, characterization and identification of cysteine desulfhydrase of Corynebacterium glutamicum, and its relationship to cysteine production

We highly purified the enzyme having L-cysteine desulfhydrase activity from Corynebacterium glutamicum. According to its partial amino acid sequence, the enzyme was identified as the aecD gene product, a C-S lyase with alpha, beta-elimination activity [I. Rossol and A. Pühler (1992) J. Bacteriol. 174, 2968-2977]. To produce L-cysteine in C. glutamicum, the Escherichia coli-altered cysE gene encoding Met256Ile mutant serine acetyltransferase, which is desensitized to feedback inhibition by L-cysteine, was introduced into C. glutamicum. When the altered cysE gene was expressed in the aecD-disrupted strain, the transformants produced approximately 290 mg of L-cysteine plus L-cystine per liter from glucose. The produced amount of these amino acids was about two-fold higher than that of the wild-type strain.

Metabolic engineering for L-lysine production by Corynebacterium glutamicum

Corynebacterium glutamicum has been used since several decades for the large-scale production of amino acids, esp. L-glutamate and L-lysine. After initial successes of random mutagenesis and screening approaches, further strain improvements now require a much more rational design, i.e. metabolic engineering. Not only recombinant DNA technology but also mathematical modelling of metabolism as well as metabolic flux analysis represent important metabolic engineering tools. This review covers as state-of-the-art examples of these techniques the genetic engineering of the L-lysine biosynthetic pathway resulting in a vectorless strain with significantly increased dihydrodipicolinate synthase activity, and the detailed metabolic flux analysis by 13C isotopomer labelling strategies of the anaplerotic enzyme activities in C. glutamicum resulting in the identification of gluconeogenic phosphoenolpyruvate carboxykinase as a limiting enzyme.

X-ray structure of MalY from Escherichia coli: a pyridoxal 5'-phosphate-dependent enzyme acting as a modulator in mal gene expression

MalY represents a bifunctional pyridoxal 5'-phosphate-dependent enzyme acting as a beta-cystathionase and as a repressor of the maltose regulon. Here we present the crystal structures of wild-type and A221V mutant protein. Each subunit of the MalY dimer is composed of a large pyridoxal 5'-phosphate-binding domain and a small domain similar to aminotransferases. The structural alignment with related enzymes identifies residues that are generally responsible for beta-lyase activity and depicts a unique binding mode of the pyridoxal 5'-phosphate correlated with a larger, more flexible substrate-binding pocket. In a screen for MalY mutants with reduced mal repressor properties, mutations occurred in three clusters: I, 83-84; II, 181-189 and III, 215-221, which constitute a clearly distinguished region in the MalY crystal structure far away from the cofactor. The tertiary structure of one of these mutants (A221V) demonstrates that positional rearrangements are indeed restricted to regions I, II and III. Therefore, we propose that a direct protein-protein interaction with MalT, the central transcriptional activator of the maltose system, underlies MalY-dependent repression of the maltose system.

Hemoxidation and binding of the 46-kDa cystalysin of Treponema denticola leads to a cysteine-dependent hemolysis of human erythrocytes

Cystalysin, a 46-kDa protein isolated from the cytosol of Treponema denticola, was capable of both cysteine dependent hemoxidation and hemolysis of human and sheep red blood cells. The activities were characteristic of a cysteine desulfhydrase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western immunoblotting analysis of the interaction of cystalysin with the red blood cells revealed an interaction of the protein with the red blood cell membrane. Substrates for the enzyme (including L-cysteine and beta-chloroalanine) enhanced the interaction, which occurred with both whole red blood cells as well as with isolated and purified red blood cell ghosts. SDS-PAGE and western immunoblotting employing anti-hemoglobin serum revealed that, during the hemoxidative events, the hemoglobin molecule associated with the red blood cell membrane, forming putative Heinz bodies. Spectrophotometric analysis of the hemoxidative events (cystalysin + cysteine + red blood cells) revealed a chemical modification of the native hemoglobin to sulfhemoglobin and methemoglobin. Hemoxidation also resulted in the degradation of both the red blood cell alpha- and beta-spectrin. The results presented suggest that the interaction of cystalysin with the red blood cell membrane results in the chemical oxidation of the hemoglobin molecule as well as an alteration in the red blood cell membrane itself.

Cystalysin, a 46-kilodalton cysteine desulfhydrase from Treponema denticola, with hemolytic and hemoxidative activities

A 46-kDa hemolytic protein, referred to as cystalysin, from Treponema denticola ATCC 35404 was overexpressed in Escherichia coli LC-67. Both the native and recombinant 46-kDa proteins were purified to homogeneity. Both proteins expressed identical biological and functional characteristics. In addition to its biological function of lysing erythrocytes and hemoxidizing the hemoglobin to methemoglobin, cystalysin was also capable of removing the sulfhydryl and amino groups from selected S-containing compounds (e.g., cysteine) producing H2S, NH3, and pyruvate. This cysteine desulfhydrase resulted in the following Michaelis-Menten kinetics: Km = 3.6 mM and k(cat) = 12 s(-1). Cystathionine and S-aminoethyl-L-cysteine were also substrates for the protein. Gas chromatography-mass spectrometry and high-performance liquid chromatography analysis of the end products revealed NH3, pyruvate, homocysteine (from cystathionine), and cysteamine (from S-aminoethyl-L-cysteine). The enzyme was active over a broad pH range, with highest activity at pH 7.8 to 8.0. The enzymatic activity was increased by beta-mercaptoethanol. It was not inhibited by the proteinase inhibitor TLCK (N alpha-p-tosyl-L-lysine chloromethyl ketone), pronase, or proteinase K, suggesting that the functional site was physically protected or located in a small fragment of the polypeptide. We hypothesize that cystalysin is a pyridoxal-5-phosphate-containing enzyme, with activity of an alphaC-N and betaC-S lyase (cystathionase) type. Since large amounts of H2S have been reported in deep periodontal pockets, cystalysin may also function in vivo as an important virulence molecule.

A physical and genetic map of the Corynebacterium glutamicum ATCC 13032 chromosome

A combined physical and genetic map of the Corynebacterium glutamicum ATCC 13032 chromosome was constructed using pulsed-field gel electrophoresis (PFGE) and hybridizations with cloned gene probes. Total genomic DNA was digested with the meganucleases SwaI (5'-ATTTAAAT-3'), PacI (5'-TTAATTAA-3'), and PmeI (5'-GTTTAAAC-3') yielding 26,27, and 23 fragments, respectively. The chromosomal restriction fragments were then separated by PFGE. By summing up the lengths of the fragments generated with each of the three enzymes, a genome size of 3082 +/- 20 kb was determined. To identify adjacent SwaI fragments, a genomic cosmid library of C.glutamicum was screened for chromosomal inserts containing SwaI sites. Southern blots of the PFGE gels were hybridized with these linking clones to connect the SwaI fragments in their natural order. By this method, about 90% of the genome could be ordered into three contigs. Two of the remaining gaps were closed by cross-hybridization of blotted SwaI digests using as probes PacI and PmeI fragments isolated from PFGE gels. The last gap in the chromosomal map was closed by hybridization experiments using partial SwaI digestions, thereby proving the circularity of the chromosome. By hybridization of gene probes to SwaI fragments separated by PFGE about 30 genes, including rRNA operons, IS element and transposon insertions were localized on the physical map.

The 46-kilodalton-hemolysin gene from Treponema denticola encodes a novel hemolysin homologous to aminotransferases

The 46-kDa hemolysin produced by Treponema denticola may be involved in the etiology of periodontitis. In order to initiate a genetic analysis of the role of this protein in disease, its gene has been cloned. Synthetic oligonucleotides, designed on the basis of the previously reported amino-terminal amino acid sequence of the 45-kDa hemolysin, were used as primers in a PCR to amplify part of the hemolysin (hly) gene. This PCR product was then used to clone the entire hly gene from libraries of T. denticola genomic DNA. Constructs containing the entire cloned region on plasmids in Escherichia coli produced both hemolysis and hemoxidation activities either on sheep blood agar plates or in liquid assays. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot (immunoblot) analysis revealed that the constructs synthesized a protein with molecular size of about 46 kDa which was reactive with anti-T. denticola hemolysin. Nucleotide sequence analysis indicated that the largest open reading frame could encode a protein with a calculated molecular size of 46.2 kDa. The first 31 amino acids encoded by this open reading frame were identical to the experimentally determined amino-terminal sequence of the 45-kDa hemolysin. These results indicate that the entire hly gene has been cloned. The deduced amino acid sequence of the T. denticola hly gene is homologous (23 to 37% identity) to those of proteins that are members of a family of pyridoxal-phosphate-dependent aminotransferases. This suggests that the 46-kDa hemolysin may be related to an aminotransferase and have a novel mechanism of hemolysis. However, the functional aspects of this relationship remain to be investigated.

MalY of Escherichia coli is an enzyme with the activity of a beta C-S lyase (cystathionase)

The Escherichia coli maltose system consists of a number of genes whose products are involved in the uptake and metabolism of maltose and maltodextrins. MalT is the central positive gene activator of the regulon and is, together with the cyclic AMP-catabolite gene activator protein system, necessary for the expression of the maltose genes. Expression of malY, a MalT-independent gene, leads to the repression of all MalT-dependent genes. We have purified MalY to homogeneity and found it to be a pyridoxal-5-phosphate-containing enzyme with the enzymatic activity of a beta C-S lyase (cystathionase). MalY is a monomeric protein of 42,000 to 44,000 Da. Strains expressing MalY constitutively abolish the methionine requirement of metC mutants. The enzymatic activity of MetC, the cleavage of cystathionine to homocysteine, ammonia, and pyruvate, can be catalyzed by MalY. However, the cystathionase activity is not required for the function of MalY in repressing the maltose system. By site-directed mutagenesis, we changed the conserved lysine residue at the pyridoxal phosphate binding site (position 233) of MalY to isoleucine. This abolished beta C-S lyase activity but not the ability of the protein to repress the maltose system. Also, the overexpression of plasmid-encoded metC did not affect mal gene expression, nor did the deduced amino acid sequence of MetC show homology to that of MalY.

Recent advances in the physiology and genetics of amino acid-producing bacteria

Corynebacterium glutamicum and its close relatives, C. flavum and C. lactofermentum, have been used for over 3 decades in the industrial production of amino acids by fermentation. Since 1984, several research groups have started programs to develop metabolic engineering principles for amino acid-producing Corynebacterium strains. Initially, the programs concentrated on the isolation of genes encoding (deregulated) biosynthetic enzymes and the development of general molecular biology tools such as cloning vectors and DNA transfer methods. With most of the genes and tools now available, recombinant DNA technology can be applied in strain improvement. To accomplish these improvements, it is critical and advantageous to understand the mechanisms of gene expression and regulation as well as the biochemistry and physiology of the species being engineered. This review explores the advances made in the understanding and application of amino acid-producing bacteria in the early 1990s.

Molecular aspects of lysine, threonine, and isoleucine biosynthesis in Corynebacterium glutamicum

The Gram-positive bacterium Corynebacterium glutamicum is used for the industrial production of amino acids, e.g. of L-glutamate and L-lysine. In the last ten years genetic engineering methods were developed for C. glutamicum and consequently, recombinant DNA technology was employed to study the biosynthetic pathways and to improve the amino acid productivity by manipulation of enzymatic, transport and regulatory functions of this bacterium. The present review summarizes the current knowledge on the synthesis and over-production of the aspartate derived amino acids L-lysine, L-threonine and L-isoleucine in C. glutamicum. A special feature of C. glutamicum is its ability to convert the lysine intermediate piperideine2,6-dicarboxylate to diaminopimelate by two different routes, i.e. by reactions involving succinylated intermediates or by the single reaction of diaminopimelate dehydrogenase. The flux distribution over the two pathways is regulated by the ammonium availability. The overall carbon flux from aspartate to lysine, however, is governed by feedback-control of the aspartate kinase and by the level of dihydrodipicolinate synthase. Consequently, expression of lysCFBR encoding a deregulated aspartate kinase and/or the overexpression of dapA encoding dihydrodipicolinate synthase led to overproduction of lysine. As a further specific feature C. glutamicum possesses a specific lysine export carrier which shows high activity in lysine overproducing mutants. Threonine biosynthesis is in addition to control by the aspartate kinase tightly regulated at the level of homoserine dehydrogenase which is subject to feedback-inhibition and to repression. C. glutamicum strains possessing a deregulated aspartate kinase and a deregulated homoserine dehydrogenase produce lysine and threonine. Amplification of deregulated homoserine dehydrogenase in such strains led to an almost complete redirection of the carbon flux to threonine. For a further flux from threonine to isoleucine the allosteric control of threonine dehydratase and of the acetohydroxy acid synthase are important. The expression of the genes encoding the latter enzyme is additionally regulated at the transcriptional level. By addition of 2-oxobutyrate as precursor and by bypassing the expression control of the acetohydroxy acid synthase genes high isoleucine overproduction can be obtained.