Biocatalytic reactions, crystal structures and mechanisms of kynurenine formamidases

Kynurenine (Kyn) as a non-proteinogenic amino acid, is prevalent in various bioactive natural products, and plays a pivotal role in metabolism and related diseases. Thus, several synthetic methods toward Kyn have been established with the employment of acid/base-mediated hydrolysis reaction to remove the formyl group of N-formylkynurenine (NFK), which is not satisfied with the trend of green chemistry. Learning from nature, kynurenine formamidase is considered a promising biocatalyst to realize the hydrolysis of NFK as alternative to the environmentally unfriendly acid or base. For these reasons, interest in the kynurenine formamidase has increased, but the research area still remains relatively underexplored. In this review, the recent investigations on the biocatalytic reactions, crystal structures and mechanisms of the kynurenine formamidases in combination with the homologous enzymes with inferred kynurenine formamidase activity are summarized. This review may help researchers understand kynurenine formamidase further and apply them in the preparation of Kyn for natural products synthesis and drug development.