Biochemical characterization of recombinant phosphoglucose isomerase of Mycobacterium tuberculosis

Characterization of the enzyme kinetics of EMP and HMP pathway in Corynebacterium glutamicum: reference for modeling metabolic networks

The model of intracellular metabolic network based on enzyme kinetics parameters plays an important role in understanding the intracellular metabolic process of Corynebacterium glutamicum, and constructing such a model requires a large number of enzymological parameters. In this work, the genes encoding the relevant enzymes of the EMP and HMP metabolic pathways from Corynebacterium glutamicum ATCC 13032 were cloned, and engineered strains for protein expression with E.coli BL21 and P.pastoris X33 as hosts were constructed. The twelve enzymes (GLK, GPI, TPI, GAPDH, PGK, PMGA, ENO, ZWF, RPI, RPE, TKT, and TAL) were successfully expressed and purified by Ni2+ chelate affinity chromatography in their active forms. In addition, the kinetic parameters (V max, K m, and K cat) of these enzymes were measured and calculated at the same pH and temperature. The kinetic parameters of enzymes associated with EMP and the HMP pathway were determined systematically and completely for the first time in C.glutamicum. These kinetic parameters enable the prediction of key enzymes and rate-limiting steps within the metabolic pathway, and support the construction of a metabolic network model for important metabolic pathways in C.glutamicum. Such analyses and models aid in understanding the metabolic behavior of the organism and can guide the efficient production of high-value chemicals using C.glutamicum as a host.

Metabolomics of Central Carbon Metabolism in Mycobacterium tuberculosis

Metabolism is a biochemical activity of all cells, thought to fuel the physiologic needs of a given cell in a quantitative, rather than qualitatively specific, manner. Mycobacterium tuberculosis is a chronic facultative intracellular pathogen that resides in humans as its only known host and reservoir. Within humans, M. tuberculosis resides chiefly in the macrophage phagosome, the cell type and compartment most committed to its eradication. M. tuberculosis thus occupies the majority of its decades-long life cycle in a state of slowed or arrested replication. At the same time, M. tuberculosis remains poised to reenter the cell cycle to ensure its propagation as a species. M. tuberculosis has thus evolved its metabolic network to both maintain and propagate its survival as a species within a single host. Knowledge of the specific ways in which its metabolic network serves these distinct though interdependent functions, however, remains highly incomplete. In this article we review existing knowledge of M. tuberculosis's central carbon metabolism as reported by studies of its basic genetic and biochemical composition, regulation, and organization, with the hope that such knowledge will inform our understanding of M. tuberculosis's ability to traverse the stringent and heterogeneous niches encountered in the host.

Cloning, biochemical characterisation, tissue localisation and possible post-translational regulatory mechanism of the cytosolic phosphoglucose isomerase from developing sunflower seeds

Lipid biosynthesis in developing sunflower (Helianthus annuus L.) seeds requires reducing power. One of the main sources of cellular NADPH is the oxidative pentose phosphate pathway (OPPP), generated from the oxidation of glucose-6-phosphate. This glycolytic intermediate, which can be imported to the plastid and enter in the OPPP, is the substrate and product of cytosolic phosphoglucose isomerase (cPGI, EC 5.3.1.9). In this report, we describe the cloning of a full-length cDNA encoding cPGI from developing sunflower seeds. The sequence was predicted to code for a protein of 566 residues characterised by the presence of two sugar isomerase domains. This cDNA was heterologously expressed in Escherichia coli as a His-tagged protein. The recombinant protein was purified using immobilised metal ion affinity chromatography and biochemically characterised. The enzyme had a specific activity of 1,436 micromol min(-1) mg(-1) and 1,011 micromol min(-1) mg(-1) protein when the reaction was initiated with glucose-6-phosphate and fructose-6-phosphate, respectively. Activity was not affected by erythrose-4-phosphate, but was inhibited by 6-P gluconate and glyceraldehyde-3-phosphate. A polyclonal immune serum was raised against the purified enzyme, allowing the study of protein levels during the period of active lipid synthesis in seeds. These results were compared with PGI activity profiles and mRNA expression levels obtained from Q-PCR studies. Our results point to the existence of a possible post-translational regulatory mechanism during seed development. Immunolocalisation of the protein in seed tissues further indicated that cPGI is highly expressed in the procambial ring.

Structural studies of phosphoglucose isomerase from Mycobacterium tuberculosis H37Rv

Phosphoglucose isomerase (PGI) plays a key role in both glycolysis and gluconeogenesis inside the cell, whereas outside the cell it exhibits cytokine properties. PGI is also known to act as an autocrine motility factor, a neuroleukin agent and a differentiation and maturation mediator. Here, the first crystal structure of PGI from Mycobacterium tuberculosis H37Rv (Mtb) is reported. The structure was refined at 2.25 A resolution and revealed the presence of one molecule in the asymmetric unit with two globular domains. As known previously, the active site of Mtb PGI contains conserved residues including Glu356, Glu216 and His387 (where His387 is from the neighbouring molecule). The crystal structure of Mtb PGI was observed to be rather more similar to human PGI than other nonbacterial PGIs, with only a few differences being detected in the loops, arm and hook regions of the human and Mtb PGIs, suggesting that the M. tuberculosis enzyme uses the same enzyme mechanism.

Expression of adipose differentiation-related protein (ADRP) and perilipin in macrophages infected with Mycobacterium leprae

Mycobacterium leprae survives and replicates within a lipid droplet stored in the enlarged phagosome of histiocytes, a typical feature of lepromatous leprosy that is thought to be an important nutrient source for the bacillus. However, the underlying mechanisms by which lipids accumulate within phagosomes remain unclear. Recently, it was revealed that the lipid droplet-associated proteins, including ADRP and perilipin, play essential roles in lipid accumulation in adipocytes or macrophages. Therefore, we attempted to examine the role of these proteins in leprosy pathogenesis. ADRP and perilipin localized to the phagosomal membrane, which contains M. leprae in skin biopsy specimens of lepromatous leprosy. ADRP expression was transiently increased after phagocytosis in THP-1 cells. However, high levels of ADRP expression persisted only when live M. leprae, but not dead bacilli or latex beads, was added. Furthermore, although peptidoglycan, a Toll-like receptor 2 ligand, suppressed the expression levels of ADRP and perilipin, M. leprae infection inhibited this suppression. These results suggest that live M. leprae has the ability to actively induce and support ADRP/perilipin expression to facilitate the accumulation of lipids within the phagosome and to further maintain a suitable environment for the intracellular survival within the macrophage.

A glucose kinase from Mycobacterium smegmatis

Carbon metabolism and regulation is poorly understood in mycobacteria, a genus that includes some major pathogenic species like Mycobacterium tuberculosis and Mycobacterium leprae. Here, we report the identification of a glucose kinase from Mycobacterium smegmatis. This enzyme serves in glucose metabolism and global carbon catabolite repression in the related actinomycete Streptomyces coelicolor. The gene, msmeg1356 (glkA), was found by means of in silico screening. It was shown that it occurs in the same genetic context in all so far sequenced mycobacterial species, where it is located in a putative tricistronic operon together with a glycosyl hydrolase and a putative malonyl-CoA transacylase. Heterologous expression of glkA in an Escherichia coli glucose kinase mutant led to the restoration of glucose growth, which provided in vivo evidence for glucose kinase function. GlkA(Msm) was subsequently overproduced in order to study its enzymatic features. We found that it can form a dimer and that it efficiently phosphorylates glucose at the expense of ATP. The affinity constant for glucose was with 9 mM about eight times higher and the velocity was about tenfold slower when compared to the parallel measured glucose kinase of S. coelicolor. Both enzymes showed similar substrate specificity, which consists in an ATP-dependent phosphorylation of glucose and no, or very inefficient, phosphorylation of the glucose analogues 2-deoxyglucose and methyl alpha-glucoside. Hence, our data provide a basis for studying the role of mycobacterial glucose kinase in vivo to unravel possible catalytic and regulatory functions.

Biochemical and functional characterization of UDP-galactose 4-epimerase from Aeromonas hydrophila

Bacteria of genus Aeromonas, responsible for a variety of pathological conditions in humans and fish, are ubiquitous waterborne bacteria. Aeromonas produces several virulent factors including a complex of lipopolysaccharide and surface array protein, involved in colonization. UDP-galactose 4-epimerase (GalE) catalyzes the production of UDP-galactose, a precursor for lipopolysaccharide biosynthesis, and thus is an important drug target. GalE exhibits interspecies variation and heterogeneity at its structural and functional level and therefore, the differences between the GalE of the host and the pathogen can be exploited for drug designing. In the present study, we report biochemical and functional characterization of the recombinant GalE of Aeromonas hydrophila. Unlike GalE reported from all other species, the purified recombinant GalE of A. hydrophila was found to exist as a monomer. This is the first report of UDP-galactose 4-epimerase from any species being a monomer. The molecular mass of the 6xHis-rGalE was determined to be 38271.477 (m/z). The 6xHis-rGalE with a K(m) of 0.5 mM for UDP-galactose exhibited optimum activity at 37 degrees C and pH 8-9. Spectrofluorimetric and CD analysis confirmed that the thermal inactivation was due to structural changes and not due to the NAD-dissociation. A relatively more ordered structure of the enzyme at pH 8 and 9 as compared to that at pH 6 or 7 suggests a key role of the electrostatic interactions in maintaining its native tertiary structure.

Crystallization and preliminary X-ray characterization of phosphoglucose isomerase from Mycobacterium tuberculosis H37Rv

Phosphoglucose isomerase is a ubiquitous enzyme that catalyzes the isomerization of D-glucopyranose-6-phosphate to D-fructofuranose-6-phosphate. The present investigation reports the expression, purification, crystallization and preliminary crystallographic studies of the phosphoglucose isomerase from Mycobacterium tuberculosis H37Rv, which shares 46% sequence identity with that of its human host. The recombinant protein, which was prepared using an Escherichia coli expression system, was crystallized by the hanging-drop vapour-diffusion method. The crystals diffracted to a resolution of 2.8 A and belonged to the orthorhombic space group I2(1)2(1)2(1), with unit-cell parameters a = 109.0, b = 119.8, c = 138.9 A.

Functional phosphoglucose isomerase from Mycobacterium tuberculosis H37Rv: Rapid purification with high yield and purity

Phosphoglucose isomerase (PGI) EC 5.3.1.9, is a housekeeping enzyme that catalyzes the reversible isomerization of d-glucopyranose-6-phosphate and d-fructofuranose-6-phosphate. We have previously reported expression and multistep purification of recombinant PGI from Mycobacterium tuberculosis using conventional methods. We now describe an improved and simplified single step approach for purification of functionally active mycobacterial rPGI. The gene encoding PGI from M. tuberculosis H37Rv was cloned in bacterial expression vector pET22b(+). Expression of recombinant PGI with six-histidine-tag protein was observed both in the soluble fraction and inclusion bodies. Approximately 116mg of recombinant enzyme was purified to near homogeneity with approximately 80% yield from the soluble fraction of 1L culture at shake flask level using one step Ni-NTA affinity chromatography. The specific activity of the purified six-histidine-tagged recombinant PGI (rPGI-His(6)) was approximately 800U/mg of protein. The apparent K(m) value of the active recombinant protein followed Michaelis-Menten kinetics and was 0.27+/-0.03mM. K(i) for the competitive inhibitor 6-phosphogluconate was 0.75mM. The enzyme had pH optima in the range of pH 7.6-9.0 and was stable up to 55 degrees C. rPGI-His(6) exhibited enzyme activity almost equal to that of enzyme without histidine tag.

Molecular characterization of a glucokinase with broad hexose specificity from Bacillus sphaericus strain C3-41

Bacillus sphaericus cannot metabolize sugar since it lacks several of the enzymes necessary for glycolysis. Our results confirmed the presence of a glucokinase-encoding gene, glcK, and a phosphofructokinase-encoding gene, pfk, on the bacterial chromosome and expression of glucokinase during vegetative growth of B. sphaericus strains. However, no phosphoglucose isomerase gene (pgi) or phosphoglucose isomerase enzyme activity was detected in these strains. Furthermore, one glcK open reading frame was cloned from B. sphaericus strain C3-41 and then expressed in Escherichia coli. Biochemical analysis revealed that this gene encoded a protein with a molecular mass of 33 kDa and that the purified recombinant glucokinase had K(m) values of 0.52 and 0.31 mM for ATP and glucose, respectively. It has been proved that this ATP-dependent glucokinase can also phosphorylate fructose and mannose, and sequence alignment of the glcK gene indicated that it belongs to the ROK protein family. It is postulated that the absence of the phosphoglucose isomerase-encoding gene pgi in B. sphaericus might be one of the reasons for the inability of this bacterium to metabolize carbohydrates. Our findings provide additional data that further elucidate the specific metabolic pathway and could be used for genetic improvement of B. sphaericus.

Biochemical and functional characterization of triosephosphate isomerase fromMycobacterium tuberculosisH37Rv

Triosephosphate isomerase (TPI), one of the key enzymes of the glycolytic pathway, is an attractive drug target against Mycobacterium tuberculosis as glycolysis provides the majority of the organism's energy requirements inside macrophages. To carry out biochemical and biophysical characterization, purified recombinant M. tuberculosis TPI produced in Escherichia coli was used. Mass spectrum analysis showed M. tuberculosis rTPI to be of 28 213 Da. The biologically active enzyme is a homodimer as determined by gel filtration chromatography. The M. tuberculosis TPI had a pH optimum in the range of 6-8 and a temperature optimum around 37 degrees C. Circular dichroism spectra analysis revealed that loss of secondary structure of rTPI occurs around 60 degrees C. Metal cations were not required for M. tuberculosis TPI activity. The k(cat) was 4.1 x 10(6) min(-1). Importantly, the apparent K(m) value of M. tuberculosis rTPI for the substrate glyceraldehyde-3-phosphate is 84 microM which is sevenfold higher than the value reported for human TPI. The difference in K(m) is indicative of the difference in the active site of the human and M. tuberculosis TPI, which can be exploited for drug designing specifically targeting M. tuberculosis TPI.