STUDIES ON THE INHIBITOR-BINDING SITE OF PORCINE ALDEHYDE REDUCTASE -CRYSTAL-STRUCTURE OF THE HOLOENZYME-INHIBITOR TERNARY COMPLEX

Aldehyde reductase is an enzyme capable of metabolizing a wide variety of aldehydes to their corresponding alcohols. The tertiary structures of aldehyde reductase and aldose reductase are similar and consist of an alpha/beta-barrel with the active site located at the carboxy term inus of the strands of the barrel. We have determined the X-ray crysta l structure of porcine aldehyde reductase holoenzyme in complex with a n aldose reductase inhibitor, tolrestat, at 2.4 Angstrom resolution to obtain a picture of the binding conformation of inhibitors to aldehyd e reductase. Tolrestat binds in the active site pocket of aldehyde red uctase and interacts through van der Waals contacts with Arg 312 and A sp 313. The carboxylate group of tolrestat is within hydrogen bonding distance with His 113 and Trp 114. Mutation of Arg 312 to alanine in p orcine aldehyde reductase alters the potency of inhibition of the enzy me by aldose reductase inhibitors. Our results indicate that the struc ture of the inhibitor-binding site of aldehyde reductase differs from that of aldose reductase due to the participation of nonconserved resi dues in its formation. A major difference is the participation of Arg 312 and Asp 313 in lining the inhibitor-binding site in aldehyde reduc tase but not in aldose reductase. (C) 1997 Wiley-Liss, Inc.