title: Enantioselective cascade biocatalysis for deracemization of 2-hydroxy acids using a three-enzyme system.
abstract: BACKGROUND
  Enantiopure 2-hydroxy acids are key intermediates for the synthesis of pharmaceuticals and fine chemicals. We present an enantioselective cascade biocatalysis using recombinant microbial cells for deracemization of racemic 2-hydroxy acids that allows for efficient production of enantiopure 2-hydroxy acids.
  
  
  RESULTS
  The method was realized by a single recombinant Escherichia coli strain coexpressing three enzymes: (S)-2-hydroxy acid dehydrogenase, (R)-2-keto acid reductase and glucose dehydrogenase. One enantiomer [(S)-2-hydroxy acid] is firstly oxidized to the keto acid with (S)-2-hydroxy acid dehydrogenase, while the other enantiomer [(R)-2-hydroxy acid] remains unchanged. Then, the keto acid obtained reduced to the opposite enantiomer with (R)-2-keto acid reductase plus cofactor regeneration enzyme glucose dehydrogenase subsequently. The recombinant E. coli strain coexpressing the three enzymes was proven to be a promising biocatalyst for the cascade bioconversion of a structurally diverse range of racemic 2-hydroxy acids, giving the corresponding (R)-2-hydroxy acids in up to 98.5 % conversion and >99 % enantiomeric excess.
  
  
  CONCLUSIONS
  In summary, a cascade biocatalysis was successfully developed to prepare valuable (R)-2-hydroxy acids with an efficient three-enzyme system. The developed elegant cascade biocatalysis possesses high atom efficiency and represents a promising strategy for production of highly valued (R)-2-hydroxy acids.
authors.affiliation: Key Laboratory of Bioorganic Synthesis of Zhejiang Province, College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou, 310014, People's Republic of China.
authors.forename: Ya-Ping
authors.initials: YP
authors.lastname: Xue
authors.affiliation: Key Laboratory of Bioorganic Synthesis of Zhejiang Province, College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou, 310014, People's Republic of China.
authors.forename: Hao
authors.initials: H
authors.lastname: Zeng
authors.affiliation: Yosemade Pharmaceutical Co. Ltd., Jinhua, 321025, People's Republic of China.
authors.forename: Xiao-Lu
authors.initials: XL
authors.lastname: Jin
authors.affiliation: Key Laboratory of Bioorganic Synthesis of Zhejiang Province, College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou, 310014, People's Republic of China.
authors.forename: Zhi-Qiang
authors.initials: ZQ
authors.lastname: Liu
authors.affiliation: Key Laboratory of Bioorganic Synthesis of Zhejiang Province, College of Biotechnology and Bioengineering, Zhejiang University of Technology, Hangzhou, 310014, People's Republic of China. zhengyg@zjut.edu.cn.
authors.forename: Yu-Guo
authors.initials: YG
authors.lastname: Zheng
keywords: 2-hydoxy acids; Cascade biocatalysis; Coexpression; Deracemization