Analysis of in vivo function of predicted isoenzymes:a metabolomic approach.

Isoenzymes occur in all organisms. Often, they are regulated with respect to environmental perturbations to assure metabolic flexibility. In bioinformatics-driven functional genome annotations, the presence of isoenzymes is frequently predicted. It is desirable to verify the functions of putative isoenzymes experimentally for a correct estimation of the metabolic capacities in a given organism. Using metabolome analysis, we investigated two knockout mutants of putative shikimate dehydrogenases (SDH) in Corynebacterium glutamicum (C. glutamicum). Here, we show that different metabolic responses to defined gene deactivations of the putative SDHs clearly indicate different functions of these enzymes. Our investigation revealed that the gene product of open reading frame Cg1835 is the essential SDH in C. glutamicum, whereas it is more likely that the gene product of the open reading frame Cg1283 belongs to the SDH-like enzyme family (SDH-L). The results of the metabolome analysis are verified with two independent methods. First, by in vitro characterization of kinetic constants after heterologous expression, and second, by measurement of SDH activity in raw cell extracts.

Crystallization and preliminary X-ray analysis of a cold-active endo-ß-1,4-D-xylanase from glycoside hydrolase family 8.

Endo-ß-1,4-D-xylanases are used in a multitude of industrial applications. Native crystals of a cold-adapted xylanase from glycoside hydrolase family 8 were obtained by the vapour-diffusion technique. The crystals belonged to space group I222, with unit-cell parameters a=46.6, b=110.8, c=150.2 Šat 100 K, and diffracted to 2.7 Šresolution at a synchrotron source. The asymmetric unit is likely to contain one molecule, with a VM of 2.07 Å3 Da(-1), corresponding to a solvent content of ∼40%.

Functional analysis of glycoside hydrolase family 8 xylanases shows narrow but distinct substrate specificities and biotechnological potential.

The potential of glycoside hydrolase family (GH) 8 xylanases in biotechnological applications is virtually unexplored. Therefore, the substrate preference and hydrolysis product profiles of two GH8 xylanases were evaluated to investigate their activities and substrate specificities. A GH8 xylanase from an uncultured bacterium (rXyn8) shows endo action but very selectively releases xylotriose from its substrates. It has a higher activity than the Pseudoalteromonas haloplanktis GH8 endo-xylanase (PhXyl) on xylononaose and smaller xylo-oligosaccharides. PhXyl preferably degrades xylan substrates with a high degree of polymerization. It is sterically more hindered by arabinose substituents than rXyn8, producing larger end hydrolysis products. The specificities of rXyn8 and PhXyl differ completely from these of the previously described GH8 xylanases from Bifidobacterium adolescentis (BaRexA) and Bacillus halodurans (BhRex). As reducing-end xylose-releasing exo-oligoxylanases, they selectively release xylose from the reducing end of small xylo-oligosaccharides. The findings of this study show that GH8 xylanases have a narrow substrate specificity, but also one that strongly varies between family members and is distinct from that of GH10 and GH11 xylanases. Structural comparison of rXyn8, PhXyl, BaRexA, and BhRex showed that subtle amino acid changes in the glycon as well as the aglycon subsites probably form the basis of the observed differences between GH8 xylanases. GH8 xylanases, therefore, are an interesting group of enzymes, with potential towards engineering and applications.

Structurally simple inhibitors of lanosterol 14alpha-demethylase are efficacious in a rodent model of acute Chagas disease.

We report structure-activity studies of a large number of dialkyl imidazoles as inhibitors of Trypanosoma cruzi lanosterol-14alpha-demethylase (L14DM). The compounds have a simple structure compared to posaconazole, another L14DM inhibitor that is an anti-Chagas drug candidate. Several compounds display potency for killing T. cruzi amastigotes in vitro with values of EC(50) in the 0.4-10 nM range. Two compounds were selected for efficacy studies in a mouse model of acute Chagas disease. At oral doses of 20-50 mg/kg given after establishment of parasite infection, the compounds reduced parasitemia in the blood to undetectable levels, and analysis of remaining parasites by PCR revealed a lack of parasites in the majority of animals. These dialkyl imidazoles are substantially less expensive to produce than posaconazole and are appropriate for further development toward an anti-Chagas disease clinical candidate.

1.6 angstroms structure of an NAD+-dependent quinate dehydrogenase from Corynebacterium glutamicum.

To date, three different functional classes of bacterial shikimate/quinate dehydrogenases have been identified and are referred to as AroE, SDH-L and YdiB. The enzyme AroE and the catalytically much slower SDH-L clearly prefer NADP+/NADPH as the cosubstrate and are specific for (dehydro-)shikimate, whereas in YdiB the differences in affinity for NADP+/NADPH versus NAD+/NADH as well as for (dehydro-)shikimate versus (dehydro-)quinate are marginal. These three subclasses have a similar three-dimensional fold and hence all belong to the same structural class of proteins. In this paper, the crystal structure of an enzyme from Corynebacterium glutamicum is presented that clearly prefers NAD+ as a cosubstrate and that demonstrates a higher catalytic efficiency for quinate rather than shikimate. While the kinetic constants for this enzyme clearly differ from those reported for AroE, SDH-L and YdiB, the three-dimensional structure of this protein is similar to members of these three subclasses. Thus, the enzyme described here belongs to a new functional class of the shikimate/quinate dehydrogenase family. The different substrate and cosubstrate specificities of this enzyme relative to all other known bacterial shikimate/quinate dehydrogenases are discussed by means of analyzing the crystal structure and derived models. It is proposed that in contrast to shikimate, quinate forms a hydrogen bond to the NAD+. In addition, it is suggested that the hydroxyl group of a conserved active-site threonine hydrogen bonds to quinate more effectively than to shikimate. Also, the hydroxyl group of a conserved tyrosine approaches the carboxylate group of quinate more closely than it does the carboxylate group of shikimate. Taken together, these factors most likely lead to a lower Michaelis constant and therefore to a higher catalytic efficiency for quinate. The active site of the dehydrogenase reported here is larger than those of other known shikimate/quinate dehydrogenases, which may explain why quinate is easily accommodated within the catalytic cleft.

Cloning, expression, purification and preliminary crystallographic characterization of a shikimate dehydrogenase from Corynebacterium glutamicum.

The shikimate dehydrogenase from Corynebacterium glutamicum has been cloned into an Escherichia coli expression vector, overexpressed and purified. Native crystals were obtained by the vapour-diffusion technique using 2-methyl-2,4-pentanediol as a precipitant. The crystals belong to the centred monoclinic space group C2, with unit-cell parameters a = 118.77, b = 63.17, c = 35.67 angstroms, beta = 92.26 degrees (at 100 K), and diffract to 1.64 angstroms on a synchrotron X-ray source. The asymmetric unit is likely to contain one molecule, corresponding to a packing density of 2.08 angstroms3 Da(-1) and a solvent content of about 41%.

High level expression and single-step purification of hexahistidine-tagged L-2-hydroxyisocaproate dehydrogenase making use of a versatile expression vector set.

Affinity tags as fusions to the N- or C-terminal part of proteins are valuable tools to facilitate the production and purification of proteins. In many cases, there may be the necessity to remove the tag after protein preparation to regain activity. Removal of the tag is accomplished by insertion of a unique amino acid sequence that is recognized and cleaved by a site specific protease. Here, we report the construction of an expression vector set that combines N- or C-terminal fusion to either a hexahistidine tag or Streptag with the possibility of tag removal by factor Xa or recombinant tobacco etch virus protease (rTEV), respectively. The vector set offers the option to produce different variants of the protein of interest by cloning the corresponding gene into four different Escherichia coli expression vectors. Either immobilized metal affinity chromatography or streptactin affinity chromatography can be used for the one-step purification. Furthermore, we show the successful application of the expression vector for C-terminal hexahistidine tagging. The expression and purification of His-tagged L-2-hydroxyisocaproate dehydrogenase yields fully active enzyme. The tag removal is here accomplished by a derivative of rTEV.