Engineering Aminotransferases for the Biocatalytic Production of Aromatic D-Amino Acids

Abstract

Optically pure aromatic D-amino acids, such as D-phenylalanine (D-Phe) and its derivatives, are high-value building blocks for the pharmaceutical industry. These compounds can be prepared using biocatalytic methods relying on various enzymes, including aminotransferases (ATs). ATs, also called transaminases (EC 2.6.1.X), are a subclass of pyridoxal 5′-phosphate-dependent enzymes that catalyze the transfer of the amino group from a donor substrate to a ketone acceptor. Synthesis of optically-pure amino acids using whole-cell biocatalytic cascades based on ATs possess several advantages compared to traditional chemical methods, including excellent enantioselectivity and increased process and step efficiency, which is achieved through the catalysis of multiple steps in one-pot reactions without requirement for intermediate work-ups, cofactor recycling, or toxic metals. However, enzyme biocatalysts typically need to be engineered to alter their substrate specificity or to increase their catalytic efficiency, which has limited their industrial application. Therefore, to facilitate the engineering process of ATs broadly and to produce aromatic D-amino acids, we developed a high-throughput assay for the testing of a broad range of ATs against libraries of potential substrates, and developed a biocatalytic cascade to produce optically pure aromatic D-amino acids.