Crystal structure of CHO reductase, a member of the aldo-keto reductase superfamily

Chinese hamster ovary (CHO) reductase is an enzyme belonging to the aldo-ke to reductase (AKR) superfamily that is induced by the aldehyde-containing p rotease inhibitor ALLN (Inoue, Sharma, Schimke, et al., J Biol Chem 1993;26 8: 5894), It shows 70% sequence identity to human aldose reductase (Hyndman , Takenoshita, Vera, et al,, J Biol Chem 1997;272:13286), which is a target for drug design because of its implication in diabetic complications, We h ave determined the crystal structure of CHO reductase complexed with nicoti namide adenine dinucleotide phosphate (NADP)(+) to 2.4 Angstrom resolution. Similar to aldose reductase and other AKRs, CHO reductase is an alpha/beta TIM barrel enzyme with cofactor bound in an extended conformation. All key residues involved in cofactor binding are conserved with respect to other AKR members. CHO reductase shows a high degree of sequence identity (91%) w ith another AKR member, FR-1 (mouse fibroblast growth factor-regulated prot ein), especially around the variable C-terminal end of the protein and has a similar substrate binding pocket that is larger than that of aldose reduc tase, However, there are distinct differences that can account for differen ces in substrate specificity. Trp111, which lies horizontal to the substrat e pocket in all other AKR members is perpendicular in CHO reductase and is accompanied by movement of Leu300. This coupled with movement of loops A, B , and C away from the active site region accounts for the ability of CHO re ductase to bind larger substrates, The position of Trp219 is significantly altered with respect to aldose reductase and appears to release Cys298 from steric constraints. These studies show that AKRs such as CHO reductase are excellent models for examining the effects of subtle changes in amino acid sequence and alignment on binding and catalysis, Proteins 2000;38:41-48, ( C) 2000 Wiley-Liss, Inc.