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Background   d -Amino acids are increasingly used as building blocks to produce pharmaceuticals and fine chemicals. However, establishing a universal biocatalyst for the general synthesis of  d -amino acids from cheap and readily available precursors with few by-products is challenging. In this study, we developed an efficient in vivo biocatalysis system for the synthesis of  d -amino acids from  l -amino acids by the co-expression of membrane-associated  l -amino acid deaminase obtained from  Proteus mirabilis  (LAAD),  meso -diaminopimelate dehydrogenases obtained from  Symbiobacterium thermophilum  (DAPDH), and formate dehydrogenase obtained from  Burkholderia stabilis  (FDH), in recombinant  Escherichia coli .    Results  To generate the in vivo cascade system, three strategies were evaluated to regulate enzyme expression levels, including single-plasmid co-expression, double-plasmid co-expression, and double-plasmid MBP-fused co-expression. The double-plasmid MBP-fused co-expression strain  Escherichia coli  pET-21b-MBP- laad /pET-28a- dapdh - fdh , exhibiting high catalytic efficiency, was selected. Under optimal conditions, 75 mg/mL of  E. coli  pET-21b-MBP- laad /pET-28a- dapdh - fdh  whole-cell biocatalyst asymmetrically catalyzed the stereoinversion of 150 mM  l -Phe to  d -Phe, with quantitative yields of over 99%  ee  in 24 h, by the addition of 15 mM NADP +  and 300 mM ammonium formate. In addition, the whole-cell biocatalyst was used to successfully stereoinvert a variety of aromatic and aliphatic  l -amino acids to their corresponding  d -amino acids.    Conclusions  The newly constructed in vivo cascade biocatalysis system was effective for the highly selective synthesis of  d -amino acids via stereoinversion.

Highly selective synthesis of d-amino acids via stereoinversion of corresponding counterpart by an in vivo cascade cell factory