Cloning and expression of the Zymomonas mobilis pyruvate kinase gene in Escherichia coli

Rheostatic contributions to protein stability can obscure a position's functional role

Rheostat positions, which can be substituted with various amino acids to tune protein function across a range of outcomes, are a developing area for advancing personalized medicine and bioengineering. Current methods cannot accurately predict which proteins contain rheostat positions or their substitution outcomes. To compare the prevalence of rheostat positions in homologs, we previously investigated their occurrence in two pyruvate kinase (PYK) isozymes. Human liver PYK contained numerous rheostat positions that tuned the apparent affinity for the substrate phosphoenolpyruvate (Kapp-PEP) across a wide range. In contrast, no functional rheostat positions were identified in Zymomonas mobilis PYK (ZmPYK). Further, the set of ZmPYK substitutions included an unusually large number that lacked measurable activity. We hypothesized that the inactive substitution variants had reduced protein stability, precluding detection of Kapp-PEP tuning. Using modified buffers, robust enzymatic activity was obtained for 19 previously-inactive ZmPYK substitution variants at three positions. Surprisingly, both previously-inactive and previously-active substitution variants all had Kapp-PEP values close to wild-type. Thus, none of the three positions were functional rheostat positions, and, unlike human liver PYK, ZmPYK's Kapp-PEP remained poorly tunable by single substitutions. To directly assess effects on stability, we performed thermal denaturation experiments for all ZmPYK substitution variants. Many diminished stability, two enhanced stability, and the three positions showed different thermal sensitivity to substitution, with one position acting as a "stability rheostat." The differences between the two PYK homologs raises interesting questions about the underlying mechanism(s) that permit functional tuning by single substitutions in some proteins but not in others.

The 2.4 Å structure of Zymomonas mobilis pyruvate kinase: Implications for stability and regulation

Human liver pyruvate kinase (hlPYK) catalyzes the final step in glycolysis, the formation of pyruvate (PYR) and ATP from phosphoenolpyruvate (PEP) and ADP. Fructose 1,6-bisphosphate (FBP), a pathway intermediate of glycolysis, serves as an allosteric activator of hlPYK. Zymomonas mobilis pyruvate kinase (ZmPYK) performs the final step of the Entner-Doudoroff pathway, which is similar to glycolysis in that energy is harvested from glucose and pyruvate is generated. The Entner-Doudoroff pathway does not have FBP as a pathway intermediate, and ZmPYK is not allosterically activated. In this work, we solved the 2.4 Å X-ray crystallographic structure of ZmPYK. The protein is dimeric in solution as determined by gel filtration chromatography, but crystallizes as a tetramer. The buried surface area of the ZmPYK tetramerization interface is significantly smaller than that of hlPYK, and yet tetramerization using the standard interfaces from higher organisms provides an accessible low energy crystallization pathway. Interestingly, the ZmPYK structure showed a phosphate ion in the analogous location to the 6-phosphate binding site of FBP in hlPYK. Circular Dichroism (CD) was used to measure melting temperatures of hlPYK and ZmPYK in the absence and presence of substrates and effectors. The only significant difference was an additional phase of small amplitude for the ZmPYK melting curves. We conclude that the phosphate ion plays neither a structural or allosteric role in ZmPYK under the conditions tested. We hypothesize that ZmPYK does not have sufficient protein stability for activity to be tuned by allosteric effectors as described for rheostat positions in the allosteric homologues.

PYK-SubstitutionOME: an integrated database containing allosteric coupling, ligand affinity and mutational, structural, pathological, bioinformatic and computational information about pyruvate kinase isozymes

Interpreting changes in patient genomes, understanding how viruses evolve and engineering novel protein function all depend on accurately predicting the functional outcomes that arise from amino acid substitutions. To that end, the development of first-generation prediction algorithms was guided by historic experimental datasets. However, these datasets were heavily biased toward substitutions at positions that have not changed much throughout evolution (i.e. conserved). Although newer datasets include substitutions at positions that span a range of evolutionary conservation scores, these data are largely derived from assays that agglomerate multiple aspects of function. To facilitate predictions from the foundational chemical properties of proteins, large substitution databases with biochemical characterizations of function are needed. We report here a database derived from mutational, biochemical, bioinformatic, structural, pathological and computational studies of a highly studied protein family-pyruvate kinase (PYK). A centerpiece of this database is the biochemical characterization-including quantitative evaluation of allosteric regulation-of the changes that accompany substitutions at positions that sample the full conservation range observed in the PYK family. We have used these data to facilitate critical advances in the foundational studies of allosteric regulation and protein evolution and as rigorous benchmarks for testing protein predictions. We trust that the collected dataset will be useful for the broader scientific community in the further development of prediction algorithms. Database URL https://github.com/djparente/PYK-DB.

Odd one out? Functional tuning of Zymomonas mobilis pyruvate kinase is narrower than its allosteric, human counterpart

Various protein properties are often illuminated using sequence comparisons of protein homologs. For example, in analyses of the pyruvate kinase multiple sequence alignment, the set of positions that changed during speciation ("phylogenetic" positions) were enriched for "rheostat" positions in human liver pyruvate kinase (hLPYK). (Rheostat positions are those which, when substituted with various amino acids, yield a range of functional outcomes). However, the correlation was moderate, which could result from multiple biophysical constraints acting on the same position during evolution and/or various sources of noise. To further examine this correlation, we here tested Zymomonas mobilis PYK (ZmPYK), which has <65% sequence identity to any other PYK sequence. Twenty-six ZmPYK positions were selected based on their phylogenetic scores, substituted with multiple amino acids, and assessed for changes in Kapp-PEP . Although we expected to identify multiple, strong rheostat positions, only one moderate rheostat position was detected. Instead, nearly half of the 271 ZmPYK variants were inactive and most others showed near wild-type function. Indeed, for the active ZmPYK variants, the total range of Kapp,PEP values ("tunability") was 40-fold less than that observed for hLPYK variants. The combined functional studies and sequence comparisons suggest that ZmPYK has evolved functional and/or structural attributes that differ from the rest of the family. We hypothesize that including such "orphan" sequences in MSA analyses obscures the correlations used to predict rheostat positions. Finally, results raise the intriguing biophysical question as to how the same protein fold can support rheostat positions in one homolog but not another.

The K+-Dependent and -Independent Pyruvate Kinases Acquire the Active Conformation by Different Mechanisms

Eukarya pyruvate kinases possess glutamate at position 117 (numbering of rabbit muscle enzyme), whereas bacteria have either glutamate or lysine. Those with E117 are K⁺-dependent, whereas those with K117 are K⁺-independent. In a phylogenetic tree, 80% of the sequences with E117 are occupied by T113/K114/T120 and 77% of those with K117 possess L113/Q114/(L,I,V)120. This work aims to understand these residues’ contribution to the K⁺-independent pyruvate kinases using the K⁺-dependent rabbit muscle enzyme. Residues 117 and 120 are crucial in the differences between the K⁺-dependent and -independent mutants. K⁺-independent activity increased with L113 and Q114 to K117, but L120 induced structural differences that inactivated the enzyme. T120 appears to be key in folding the protein and closure of the lid of the active site to acquire its active conformation in the K⁺-dependent enzymes. E117K mutant was K⁺-independent and the enzyme acquired the active conformation by a different mechanism. In the K⁺-independent apoenzyme of Mycobacterium tuberculosis, K72 (K117) flips out of the active site; in the holoenzyme, K72 faces toward the active site bridging the substrates through water molecules. The results provide evidence that two different mechanisms have evolved for the catalysis of this reaction.

The contribution of two isozymes to the pyruvate kinase activity of Vibrio cholerae: One K+-dependent constitutively active and another K+-independent with essential allosteric activation

In a previous phylogenetic study of the family of pyruvate kinase EC (2.7.1.40), a cluster with Glu117 and another with Lys117 were found (numbered according to the rabbit muscle enzyme). The sequences with Glu117 have been found to be K+-dependent, whereas those with Lys117 were K+-independent. Interestingly, only γ-proteobacteria exhibit sequences in both branches of the tree. In this context, it was explored whether these phylogenetically distinct pyruvate kinases were both expressed and contribute to the pyruvate kinase activity in Vibrio cholerae. The main findings of this work showed that the isozyme with Glu117 is an active K+-dependent enzyme. At the same substrate concentration, its Vmax in the absence of fructose 1,6 bisphosphate was 80% of that with its effector. This result is in accordance with the non-essential activation described by allosteric ligands for most pyruvate kinases. In contrast, the pyruvate kinase with Lys117 was a K+-independent enzyme displaying an allosteric activation by ribose 5-phosphate. At the same substrate concentration, its activity without the effector was 0.5% of the one obtained in the presence of ribose 5-phosphate, indicating that this sugar monophosphate is a strong activator of this enzyme. This absolute allosteric dependence is a novel feature of pyruvate kinase activity. Interestingly, in the K+-independent enzyme, Mn2+ may "mimic" the allosteric effect of Rib 5-P. Despite their different allosteric behavior, both isozymes display a rapid equilibrium random order kinetic mechanism. The intracellular concentrations of fructose 1,6-bisphosphate and ribose 5-phosphate in Vibrio cholerae have been experimentally verified to be sufficient to induce maximal activation of both enzymes. In addition, Western blot analysis indicated that both enzymes were co-expressed. Therefore, it is concluded that VcIPK and VcIIPK contribute to the activity of pyruvate kinase in this γ-proteobacterium.

A novel pyruvate kinase and its application in lactic acid production under oxygen deprivation in Corynebacterium glutamicum

Background

Pyruvate kinase (Pyk) catalyzes the generation of pyruvate and ATP in glycolysis and functions as a key switch in the regulation of carbon flux distribution. Both the substrates and products of Pyk are involved in the tricarboxylic acid cycle, anaplerosis and energy anabolism, which places Pyk at a primary metabolic intersection. Pyks are highly conserved in most bacteria and lower eukaryotes. Corynebacterium glutamicum is an industrial workhorse for the production of various amino acids and organic acids. Although C. glutamicum was assumed to possess only one Pyk (pyk1, NCgl2008), NCgl2809 was annotated as a pyruvate kinase with an unknown role.

Results

Here, we identified that NCgl2809 was a novel pyruvate kinase (pyk2) in C. glutamicum. Complementation of the WTΔpyk1Δpyk2 strain with the pyk2 gene restored its growth on d-ribose, which demonstrated that Pyk2 could substitute for Pyk1 in vivo. Pyk2 was co-dependent on Mn²⁺ and K⁺ and had a higher affinity for ADP than phosphoenolpyruvate (PEP). The catalytic activity of Pyk2 was allosterically regulated by fructose 1,6-bisphosphate (FBP) activation and ATP inhibition. Furthermore, pyk2 and ldhA, which encodes l-lactate dehydrogenase, were co-transcribed as a bicistronic mRNA under aerobic conditions and pyk2 deficiency had a slight effect on the intracellular activity of Pyk. However, the mRNA level of pyk2 in the wild-type strain under oxygen deprivation was 14.24-fold higher than that under aerobic conditions. Under oxygen deprivation, pyk1 or pyk2 deficiency decreased the generation of lactic acid, and the overexpression of either pyk1 or pyk2 increased the production of lactic acid as the activity of Pyk increased. Fed-batch fermentation of the pyk2-overexpressing WTΔpyk1 strain produced 60.27 ± 1.40 g/L of lactic acid, which was a 47% increase compared to the parent strain under oxygen deprivation.

Conclusions

Pyk2 functioned as a pyruvate kinase and contributed to the increased level of Pyk activity under oxygen deprivation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-016-0313-6) contains supplementary material, which is available to authorized users.

New insights on the mechanism of the K(+-) independent activity of crenarchaeota pyruvate kinases

Eukarya pyruvate kinases have glutamate at position 117 (numbered according to the rabbit muscle enzyme), whereas in Bacteria have either glutamate or lysine and in Archaea have other residues. Glutamate at this position makes pyruvate kinases K+-dependent, whereas lysine confers K+-independence because the positively charged residue substitutes for the monovalent cation charge. Interestingly, pyruvate kinases from two characterized Crenarchaeota exhibit K+-independent activity, despite having serine at the equivalent position. To better understand pyruvate kinase catalytic activity in the absence of K+ or an internal positive charge, the Thermofilum pendens pyruvate kinase (valine at the equivalent position) was characterized. The enzyme activity was K+-independent. The kinetic mechanism was random order with a rapid equilibrium, which is equal to the mechanism of the rabbit muscle enzyme in the presence of K+ or the mutant E117K in the absence of K+. Thus, the substrate binding order of the T. pendens enzyme was independent despite lacking an internal positive charge. Thermal stability studies of this enzyme showed two calorimetric transitions, one attributable to the A and C domains (Tm of 99.2°C), and the other (Tm of 105.2°C) associated with the B domain. In contrast, the rabbit muscle enzyme exhibits a single calorimetric transition (Tm of 65.2°C). The calorimetric and kinetic data indicate that the B domain of this hyperthermophilic enzyme is more stable than the rest of the protein with a conformation that induces the catalytic readiness of the enzyme. B domain interactions of pyruvate kinases that have been determined in Pyrobaculum aerophilum and modeled in T. pendens were compared with those of the rabbit muscle enzyme. The results show that intra- and interdomain interactions of the Crenarchaeota enzymes may account for their higher B domain stability. Thus the structural arrangement of the T. pendens pyruvate kinase could allow charge-independent catalysis.

Manipulation of the anoxic metabolism in Escherichia coli by ArcB deletion variants in the ArcBA two-component system

Bioprocesses conducted under conditions with restricted O(2) supply are increasingly exploited for the synthesis of reduced biochemicals using different biocatalysts. The model facultative anaerobe Escherichia coli has elaborate sensing and signal transduction mechanisms for redox control in response to the availability of O(2) and other electron acceptors. The ArcBA two-component system consists of ArcB, a membrane-associated sensor kinase, and ArcA, the cognate response regulator. The tripartite hybrid kinase ArcB possesses a transmembrane, a PAS, a primary transmitter (H1), a receiver (D1), and a phosphotransfer (H2) domain. Metabolic fluxes were compared under anoxic conditions in a wild-type E. coli strain, its ΔarcB derivative, and two partial arcB deletion mutants in which ArcB lacked either the H1 domain or the PAS-H1-D1 domains. These analyses revealed that elimination of different segments in ArcB determines a distinctive distribution of d-glucose catabolic fluxes, different from that observed in the ΔarcB background. Metabolite profiles, enzyme activity levels, and gene expression patterns were also investigated in these strains. Relevant alterations were observed at the P-enol-pyruvate/pyruvate and acetyl coenzyme A metabolic nodes, and the formation of reduced fermentation metabolites, such as succinate, d-lactate, and ethanol, was favored in the mutant strains to different extents compared to the wild-type strain. These phenotypic traits were associated with altered levels of the enzymatic activities operating at these nodes, as well as with elevated NADH/NAD(+) ratios. Thus, targeted modification of global regulators to obtain different metabolic flux distributions under anoxic conditions is emerging as an attractive tool for metabolic engineering purposes.

Glyoxylate and Pyruvate Are Antagonistic Effectors of the Escherichia coli IclR Transcriptional Regulator

The Escherichia coli isocitrate lyase regulator (IclR) regulates the expression of the glyoxylate bypass operon (aceBAK). Founding member of a large family of common fold transcriptional regulators, IclR comprises a DNA binding domain that interacts with the operator sequence and a C-terminal domain (C-IclR) that binds a hitherto unknown small molecule. We screened a chemical library of more than 150 metabolic scaffolds using a high-throughput protein stability assay to identify molecules that bind IclR and then tested the active compounds in in vitro assays of operator binding. Glyoxylate and pyruvate, identified by this method, bound the C-IclR domain with KD values of 0.9+/-0.2 and 156.2+/-7.9 microM, as defined by isothermal titration calorimetry. Both compounds altered IclR interactions with operator DNA in electrophoretic mobility shift assays but showed an antagonistic effect. Glyoxylate disrupted the formation of the IclR/operator complex in vitro by favoring the inactive dimeric state of the protein, whereas pyruvate increased the binding of IclR to the aceBAK promoter by stabilizing the active tetrameric form of the protein. Structures of the C-IclR domain alone and in complex with each effector were determined at 2.3 A, confirming the binding of both molecules in the effector recognition site previously characterized for the other representative of the family, the E. coli AllR regulator. Site-directed mutagenesis demonstrated the importance of hydrophobic patch formed by Met-146, Leu-154, Leu-220, and Leu-143 in interactions with effector molecules. In general, our strategy of combining chemical screens with functional assays and structural studies has uncovered two small molecules with antagonistic effects that regulate the IclR-dependent transcription of the aceBAK operon.

Dichotomic Phylogenetic Tree of the Pyruvate Kinase Family

K+ dependence was assumed to be a feature of all pyruvate kinases until it was discovered that some enzymes express K+ -independent activity. Almost all the K+ -independent pyruvate kinases have Lys at position 117, instead of the Glu present in the K+ -dependent muscle enzyme. Mutagenesis studies show that the internal positive charge substitutes for the K+ requirement (Laughlin, L. T. & Reed, G. H. (1997) Arch. Biochem. Biophys. 348, 262-267). In this work a phylogenetic analysis of pyruvate kinase was performed to ascertain the abundance of K+ -independent activities and to explore whether the K+ activating effect is related to the evolutionary history of the enzyme. Of the 230 studied sequences, 46% have Lys at position 117, and the rest have Glu. Pyruvate kinases with Lys117 and Glu117 are separated in two clusters. All of the enzymes of the Glu117 cluster that have been characterized are K+ -dependent, whereas those of the Lys117 cluster are K+ -independent. Thus, there is a strict correlation between the dichotomy of the tree and the dependence of activity on K+. 77% of the pyruvate kinases that possess Lys117 have Lys113/Gln114; they also have Ile, Val, or Leu at position 120. These residues are replaced by Glu117 and Thr113/Lys114/Thr120 in 80% of K+ -dependent pyruvate kinases. Structural analysis indicates that these residues are in a hinge region involved in the acquisition of the catalytic conformation of the enzyme. The route of conversion from K+ -independent to K+ -dependent pyruvate kinases is described. A plausible explanation of how enzymes developed K+ dependence is put forth.

Pyruvate kinase revisited: the activating effect of K+

For more than 50 years, it has been known that K(+) is an essential activator of pyruvate kinase (Kachmar, J. F., and Boyer, P. D. (1953) J. Biol. Chem. 200, 669-683). However, the role of K(+) in the catalysis by pyruvate kinase has not been totally understood. Previous studies without K(+) showed that the affinity of ADP-Mg(2+) depends on the concentration of phosphoenolpyruvate, although the kinetics of the enzyme at saturating K(+) concentrations show independence in the binding of substrates (Reynard, A. M., Hass, L. F., Jacobsen, D. D. & Boyer, P. D. (1961) J. Biol. Chem. 236, 2277-2283). Here, we explored the kinetics of the enzyme with and without K(+). The results show that without K(+), the kinetic mechanism of pyruvate kinase changes from random to ordered with phosphoenol-pyruvate as first substrate. V(max) with K(+) was about 400 higher than without K(+). In the presence of K(+), the affinities for phosphoenol-pyruvate, ADP-Mg(2+), oxalate, and ADP-Cr(2+) were 2-6-fold higher than in the absence of K(+). This as well as fluorescence data also indicate that K(+) is involved in the acquisition of the active conformation of the enzyme, allowing either phosphoenolpyruvate or ADP to bind independently (random mechanism). In the absence of K(+), ADP cannot bind to the enzyme until phosphoenolpyruvate forms a competent active site (ordered mechanism). We propose that K(+) induces the closure of the active site and the arrangement of the residues involved in the binding of the nucleotide.

Production of cytidine 5'-monophosphate N-acetylneuraminic acid using recombinant Escherichia coli as a biocatalyst

An Escherichia coli strain expressing three recombinant enzymes, i.e., cytidine 5'-monophosphate (CMP) kinase, sialic acid aldolase and cytidine 5'-monophosphate N-acetylneuraminic acid (CMP-NeuAc) synthetase, was utilized as a biocatalyst for the production of CMP-NeuAc. Both recombinant E. coli extract and whole cells catalyzed the production of CMP-NeuAc from CMP (20 mM), N-acetylmannosamine (40 mM), pyruvate (60 mM), ATP (1 mM), and acetylphosphate (60 mM), resulting in 90% conversion yield based on initial CMP concentration used. It was confirmed that endogenous acetate kinase can catalyze not only the ATP regeneration in the conversion of CMP to CDP but also the conversion of CDP to CTP. On the other hand, endogenous pyruvate kinase and polyphosphate kinase could not regenerate ATP efficiently. The addition of exogenous acetate kinase to the reaction mixture containing the cell extract increased the conversion rate of CMP to CMP-NeuAc by about 1.5-fold, but the addition of exogenous inorganic pyrophosphatase had no influence on the reaction. This E. coli strain could also be employed as an enzyme source for in situ regeneration of CMP-NeuAc in a sialyltransferase catalyzed reaction. About 90% conversion yield of alpha2,3-sialyl-N-acetyllactosamine was obtained from N-acetyllactosamine (20 mM), CMP (2 mM), N-acetylmannosamine (40 mM), pyruvate (60 mM), ATP (1 mM), and acetyl phosphate (80 mM) using the recombinant E. coli extract and alpha2,3-sialyltransferase.

A memorial review of Jay Bailey's contribution in prokaryotic metabolic engineering

When mentioning prokaryotic metabolic engineering, most people will immediately think of Jay Bailey. Jay's contribution to this fast-growing field is evident and familiar to many. Therefore, instead of a detailed technical review, we attempt in this article to summarize his contribution and dissect reasons for his success in this area from a standpoint of one of his former students (VH) and of a colleague in the field (JCL). This short review is by no means complete and provides only a partial view of Jay's contribution to the metabolic engineering of prokaryotes.

Molecular characterization, enzyme properties and transcriptional regulation of phosphoenolpyruvate carboxykinase and pyruvate kinase in a ruminal bacterium, Selenomonas ruminantium

To elucidate the regulatory mechanism for propionate production in Selenomonas ruminantium, the molecular properties and gene expression of phosphoenolpyruvate carboxykinase (Pck) and pyruvate kinase (Pyk) were investigated. The Pck was deduced to consist of 538 aa with a molecular mass of 59.6 kDa, and appeared to exist as a monomer. The Pyk was revealed to consist of four identical subunits consisting of 469 aa with a molecular mass of 51.3 kDa. Both Mg(2+) and Mn(2+) were required for the maximal activity of Pck, and Pck utilized ADP, not GDP or IDP, as a substrate. Either Mg(2+) or Mn(2+) was required for Pyk activity, and the enzyme was activated by phosphoenolpyruvate (PEP) and fructose 1,6-bisphosphate (FBP). Pyk activity was severely inhibited by P(i), but restored by the addition of FBP. The K:(m) value of Pck for PEP (0.55 mM) was nearly equal to the K:(m) value of Pyk for PEP, suggesting that the partition of the flow from PEP in the fermentation pathways is determined by the activity ratio of Pck to Pyk. Both pck and pyk genes were monocistronic, although two transcriptional start sites were found in pyk. The level of pyk mRNA was not different whether glucose or lactate was the energy substrate. However, the pck mRNA level was 12-fold higher when grown on lactate than on glucose. The level of pck mRNA was inversely related to the sufficiency of energy, suggesting that Pck synthesis is regulated at the transcriptional level when energy supply is altered. It was conceivable that the transcription of pck in S. ruminantium is triggered by PEP and suppressed by ATP.

Altered regulation of pyruvate kinase or co-overexpression of phosphofructokinase increases glycolytic fluxes in resting Escherichia coli

Glycolytic fluxes in resting Escherichia coli were enhanced by overexpression of heterologous pyruvate kinases (Pyk) from Bacillus stearothermophilus and Zymomonas mobilis, but not homologous Pyk. Compared to the control, an increase of 10% in specific glucose consumption and of 15% in specific ethanol production rates was found in anaerobic resting cells, expressing the heterologous Pyks, that were harvested from exponentially growing aerobic cultures. A further increase in glycolytic flux was achieved by simultaneous overexpression of E. coli phosphofructokinase (Pfk) and Pyk with specific glucose consumption and ethanol production rates of 25% and 35% greater, respectively, than the control. Fluxes to lactate were not significantly affected, contrary to previous observations with resting cells harvested from anaerobically growing cultures. To correlate the physiology of resting cells with the physiology of cells prior to harvest, we determined the relevant growth parameters from aerobic and anaerobic precultures. We conclude that glycolytic fluxes in E. coli with submaximal (aerobic) metabolic activity can be increased by overexpression of pyruvate kinases which do not require allosteric activation or co-overexpression with Pfk. However, such improvements require more extensive engineering in E. coli with near maximal (anaerobic) metabolic activity.

Molecular analysis of the Corynebacterium glutamicum transketolase gene

Transketolase is important in production of the aromatic amino acids in Corynebacterium glutamicum. The complete nucleotide sequence of the C. glutamicum transketolase gene has been identified. The DNA-derived protein sequence is highly similar to the transketolase of Mycobacterium tuberculosis, taxonomically related to C. glutamicum. The alignment of the N-terminus regions between both transketolases showed TTG to be the most probable start codon. Potential ribosomal binding and promoter regions were situated upstream from the TTG. The deduced amino acid sequence consists of 700 residues with a calculated molecular mass of 75 kDa, and contains all amino acid residues involved in cofactor and substrate binding in the well-characterized yeast transketolase sequence.