PubMed · 9434468
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N Hotta. 1997. [Epalrestat].. https://pubmed.ncbi.nlm.nih.gov/9434468/
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A xylose reductase (XR) gene was identified from the Neurospora crassa whole-genome sequence, expressed heterologously in Escherichia coli, and purified as a His6-tagged fusion in high yield. This enzyme is one of the most active XRs thus far characterized and may be used for the in vitro production of xylitol.
Yeast xylose reductases are hypothesized as hybrid enzymes as their primary sequences contain elements of both the aldo-keto reductases (AKR) and short chain dehydrogenase/reductase (SDR) enzyme families. During catalysis by members of both enzyme families, an essential Lys residue H-bonds to a Tyr residue that donates proton to the aldehyde substrate. In the Saccharomyces cerevisiae xylose reductase, Tyr49 has been identified as the proton donor. However, the primary sequence of the enzyme contains two Lys residues, Lys53 and Lys78, corresponding to the conserved motifs for SDR and AKR enzyme families, respectively, that may H-bond to Tyr49. We used site-directed mutagenesis to substitute each of these Lys residues with Met. The activity of the K53M variant was slightly decreased as compared to the wild-type, while that of the K78M variant was negligible. The results suggest that Lys78 is the essential residue that H-bonds to Tyr49 during catalysis and indicate that the active site residues of yeast xylose reductases match those of the AKR, rather than SDR, enzymes. Intrinsic enzyme fluorescence spectroscopic analysis suggests that Lys78 may also contribute to the efficient binding of NADPH to the enzyme.
The crystal structure of the complex of human recombinant aldose reductase (AR) with zenarestat, one of its potent inhibitors, has been solved at 2.5 A resolution. Zenarestat fits neatly in the hydrophobic active site and induces unique and dramatic conformational changes. For example, the benzene ring of zenarestat occupies a gap in the side chains of Leu300 and Trp111 that interact directly and forms a CH-pi interaction in the native holoenzyme. As a result, the benzene ring of the inhibitor and these side chains form a CH-pi-pi interaction. Such structural information is key to understanding the mode of action of this class of inhibitors and for rational design of better therapeutics.