Biocatalytic Reductions and Chemical Versatility of the Old Yellow Enzyme Family of Flavoprotein Oxidoreductases

The old yellow enzyme (OYE) family is a large group of flavin-dependent redox biocatalysts with major applications in the industrial reduction of activated alkenes. These enzymes have broad specificity, are relatively stable, and have been made available in large quantities by using conventional genetic methods. The catalytic cycle comprises two half-reactions: reduction of flavin mononucleotide by NAD(P)H followed by flavin oxidation through stereospecific reduction of the C=C bond of a wide range of activated alkenes. Recent years have witnessed extensive investigation of these reactions, aided by knowledge of atomic resolution structures for selected family members. In turn, this has led to deep understanding of the stereochemical course of substrate reduction and expansion of the biocatalytic versatility of this enzyme family through engineering approaches. We provide an overview of the structures, mechanisms, and chemical specificity of the reactions catalyzed by the OYE members. We provide an overview of the biocatalytic potential of this family of enzymes and illustrate the value of combining mechanistic and structural studies of biocatalysts to guide future exploitation of these enzymes in industrial biocatalysis.