Enzyme fusions in biocatalysis: Coupling reactions by pairing enzymes

One approach to bring enzymes together for multi-enzyme biocatalysis is genetic fusion. This enables production of multifunctional enzymes, which can be used for whole-cell biotransformations or for in vitro (cascade) reactions. In some cases and in some aspects, such as expression and conversions, the fused enzymes outperform the combination of the individual enzymes. On the other hand, some enzyme fusions are greatly compromised in activity and/or expression. In this review, we give an overview of studies on fusions between two or more enzymes, that were used for biocatalytic applications, with a focus on oxidative enzymes. Typically, the enzymes are paired to facilitate cofactor recycling or co-substrate supply. In addition, different linker designs are briefly discussed. Although enzyme fusion is a promising tool for some biocatalytic applications, future studies could benefit from integrating the findings of previous studies, to improve reliability and effectiveness.