Structure-guided engineering of ChKRED20 from Chryseobacterium sp. CA49 for asymmetric reduction of aryl ketoesters.

•The X-ray crystal structure of ChKRED20/NAD+ complex was solved.•Three rounds of iterative saturation mutagenesis were performed.•Mutants with increased substrate acceptance toward aryl ketoesters were achieved.•One mutant had a kcat/Km 196-fold of the wild-type.•All three substrates were completely reduced at 100 g/l loading.