1.7-ANGSTROM STRUCTURE OF FR-1, A FIBROBLAST GROWTH FACTOR-INDUCED MEMBER OF THE ALDO-KETO REDUCTASE FAMILY, COMPLEXED WITH COENZYME AND INHIBITOR

Murine FR-1 is a protein that is induced by fibroblast growth factor-1 and, therefore, may play a role in the regulation of the cell cycle. Sequence comparison indicates that it is a member of the NADPH-depende nt aldo-keto reductase family. It bears 70% identity to human aldose r eductase, an enzyme implicated in diabetic complications and a target for drug design. We have determined the 1.7 Angstrom resolution struct ure of the FR-1 in a ternary complex with NADPH and zopolrestat, a pot ent aldose reductase inhibitor. FR-1 folds into a (beta/alpha)(8) barr el with an active site characterized by a preponderance of hydrophobic residues residing in a deep oblong cavity at the C-terminal end of th e beta-barrel. The nicotinamide moiety of the coenzyme sits in the bas e of the cavity. Zopolrestat occupies the active site cavity and makes numerous contacts with several hydrophobic residues. The FR-1 ternary complex structure indicates that it uses the same general catalytic m echanism as aldose reductase and other members of the family whose str uctures have been determined. The protein exhibits reductase activity with DL-glyceraldehyde as a substrate and is strongly inhibited by zop olrestat. When compared with the structure of a similar ternary comple x of aldose reductase, the binding site retains many of the interactio ns with the coenzyme and inhibitor from the conserved residues. Some d ifferences in sequence, however, create a larger binding site that con tains six more water molecules than in the aldose reductase ternary co mplex structure. Sequence comparisons with other members of this famil y of proteins in a structural context show high conservation of active site architecture.