We report structure-activity studies of a large number of dialkyl imidazoles as inhibitors of Trypanosoma cruzi lanosterol-14α-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 antiChagas disease clinical candidate.

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.

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.

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