Structure-based rational design of a short-chain dehydrogenase/reductase for improving activity toward mycotoxin patulin

Patulin is a fatal mycotoxin that is widely detected in drinking water and fruit-derived products contaminated by diverse filamentous fungi. CgSDR from Candida guilliermondii represents the first NADPH-dependent short-chain dehydrogenase/reductase that catalyzes the reduction of patulin to the nontoxic E-ascladiol. To elucidate the catalytic mechanism of CgSDR, we solved its crystal structure in complex with cofactor and substrate. Structural analyses indicate that patulin is situated in a hydrophobic pocket adjacent to the cofactor, with the hemiacetal ring orienting toward the nicotinamide moiety of NADPH. In addition, we conducted structure-guided engi-neering to modify substrate-binding residue V187 and obtained variant V187F, V187K and V187W, whose catalytic activity was elevated by 3.9-, 2.2-and 1.7-fold, respectively. The crystal structures of CgSDR variants suggest that introducing additional aromatic stacking or hydrogen-bonding interactions to bind the lactone ring of patulin might account for the observed enhanced activity. These results illustrate the catalytic mechanism of SDR-mediated patulin detoxification for the first time and provide the upgraded variants that exhibit tremendous potentials in industrial applications.

Automated summary

Patulin, a fatal mycotoxin, is commonly found in contaminated drinking water and fruit-derived products. This study reveals the catalytic mechanism of CgSDR in reducing patulin to the nontoxic E-ascladiol and presents upgraded variants with enhanced activity through structural analysis and engineering. These findings have significant implications for industrial applications.