Molecular modeling of the aldose reductase-inhibitor complex based on the X-ray crystal structure and studies with single-site-directed mutants

Aldose reductase (AR) has been implicated in the etiology of the secondary complications of diabetes. This enzyme catalyzes the reduction of glucose t o sorbitol using nicotinamide adenine dinucleotide phosphate as an essentia l cofactor. AR has been localized at the sites of tissue damage, and inhibi tors of this enzyme prevent the development of neuropathy, nephropathy, ret inopathy, and cataract formation in animal models of diabetes. The crystal structure of AR complexed with zopolrestat, a potent inhibitor of AR, has b een described.(1) We have generated a model of the AR-inhibitor complex bas ed on the reported C alpha coordinates of the protein and results of a stru cture-activity relationship study using four structurally distinct classes of inhibitors, recombinant human AR, and four single-site-directed mutants of this enzyme. The effects of the site-directed mutations on residues with in the act ive site of the enzyme were evaluated by average interaction ene rgy calculations and by calculations of carbon atom surface area changes. T hese values correlated well with the IC50 values for zopolrestat with the w ildtype and mutant enzymes, validating the model. On the basis of the zopol restat-binding model, we have proposed binding models for 10 other AR inhib itors. Our models have enabled us to gain a qualitative understanding of th e binding domains of the enzyme and how different inhibitors impact the siz e and shape of the binding site.