Aldose and aldehyde reductases: Structure-function studies on the coenzymeand inhibitor-binding sites

PURPOSE: To identify the structural features responsible for the difference s in coenzyme and inhibitor specificities of aldose and aldehyde reductases . METHODS: The crystal structure of porcine aldehyde reductase in complex wit h NADPH and the aldose reductase inhibitor sorbinil was determined. The con tribution of each amino acid lining the coenzyme-binding site to the bindin g of NADPH was calculated using the Discover package. In human aldose reduc tase, the role of the non-conserved Pro 216 (Ser in aldehyde reductase) in the binding of coenzyme was examined by site-directed mutagenesis. RESULTS: Sorbinil binds to the active site of aldehyde reductase and is hyd rogen-bonded to Trp 22, Tyr 50, His 113, and the non-conserved Arg 312. Unl ike tolrestat, the binding of sorbinil does not induce a change in the side chain conformation of Arg 312. Mutation of Pro 216 to Ser in aldose reduct ase makes the binding of coenzyme more similar to that of aldehyde reductas e. CONCLUSIONS: The participation of non-conserved active site residues in the binding of inhibitors and the differences in the structural changes requir ed for the binding to occur are responsible for the differences in the pote ncy of inhibition of aldose and aldehyde reductases. We report that the non -conserved Pro 216 in aldose reductase contributes to the tight binding of NADPH.