Constructing a novel biosynthetic pathway for synthesis of chiral amine pharmaceutical intermediates by integrating heterologous aminotransferase in Streptomyces hygroscopucys

Aminotransferase has emerged as a powerful alternative for synthesis of chiral amines pharmaceutical intermediates to traditional chemistry via resolution. β-valienamine, as an inhibitor of β-type glycosidase with great potentials to treat lysosomal storage diseases, was chemically synthesized due to the short of natural biosynthetic pathway. Here, we explored a novel pathway in Streptomyces hygroscopucys 5008 mainly for converting prochiral valienone, an intermediate in validamycin A biosynthetic pathway, to chiral β-valienamine by integrating heterologous aminotransferase. After testing several bacterial aminotransferases, the enzyme BtrR from Bacillus circulans was verified to catalyze the transformation of  the unnatrual substrate valienone into β-valienamine with kcat/Km 1.00 mM^-1min^-1 in vitro. Furthermore, we integrated BtrR into Streptomyces hygroscopucys 5008 and knocked out its competitive gene valC. The engineered bacteria was able to produce β-valienamine with the yield of 20 mg per liter. Our work first shows that reprogramming the biosynthetic pathway could provide a new efficient route for synthesis of unnatural chiral amine module of pharmaceuticals.