Identification of D-carbamoylase for biocatalytic cascade synthesis of D-tryptophan featuring high enantioselectivity

In this study, an enantioselective D-carbamoylase (AcHyuC) was identified from Arthrobacter crystallopoietes with optimum pH of 8.5, much more compatible with hydantoinase process than other reported D-N-carbamoylases. AcHyuC has a substrate preference for aromatic carbamoyl-compounds. The dynamic kinetic resolution (DKR) cascade was developed by combining this AcHyuC with hydantoin racemase from Arthrobacter aurescens (AaHyuA) and D-hydantoinase from Agrobacterium tumefaciens (AtHyuH) for enantioselective resolution of L-indolylmethylhydantoin into D-Trp. The optimum pH of DKR cascade reaction was determined to be 8.0, and PEG 400 could facilitate the reaction. As much as 80 mM L-indolylmethylhydantoin could be fully converted to DTrp within 12 h at 0.5 L scale, with 99.4% yield,> 99.9% e. e. and productivity of 36.6 g L-1 d(-1). This study provides a new D-carbamoylase compatible with the DKR cascade for efficient production of optically pure D-Trp from L-indolylmethylhydantoin.