title: Metabolic engineering of indole pyruvic acid biosynthesis in Escherichia coli with tdiD.
abstract: BACKGROUND
  Indole pyruvic acid (IPA) is a versatile platform intermediate and building block for a number of high-value products in the pharmaceutical and food industries. It also has a wide range of applications, such as drugs for the nervous system, cosmetics, and luminophores. Chemical synthesis of IPA is a complicated and costly process. Moreover, through the biosynthesis route employing L-amino acid oxidase, the byproduct hydrogen peroxide leads the degradation of IPA. TdiD, identified as a specific tryptophan aminotransferase, could be an alternative solution for efficient IPA biosynthesis.
  
  
  RESULTS
  Escherichia coli strain W3110, which demonstrates basic production when supplied with tryptophan, was engineered for IPA biosynthesis. Several strategies were implemented to improve IPA production. First, through incorporating the codon-optimized tdiD into W3110, IPA levels increased from 41.54 ± 1.26 to 52.54 ± 2.08 mg/L. Second, after verifying the benefit of an increased phenylpyruvate pool, a YL03 strain was constructed based on a previously reported mutant strain of W3110 with a plasmid carrying aroFfbrand pheAfbrto further improve IPA production. The recombinant YL03 strain accumulated IPA at 158.85 ± 5.36 mg/L, which was 3.82-fold higher than that of the wild-type W3110 strain. Third, optimization of tdiDcoexpression was carried out by replacing the Trc promoter with a series of constitutively active promoters along with increasing the plasmid copy numbers. The highest IPA production was observed in YL08, which achieved 236.42 ± 17.66 mg/L and represented a greater than 5-fold increase as compared to W3110. Finally, the effects of deletion and overexpression of tnaA on IPA biosynthesis were evaluated. The removal of tnaA led to slightly reduced IPA levels, whereas the overexpression of tnaA resulted in a considerable decline in production.
  
  
  CONCLUSIONS
  This study illustrates the feasibility of IPA biosynthesis in E. coli through tdiD. An efficient IPA producing strain, YL08, was developed, which provides a new possibility for biosynthesis of IPA. Although the final production was limited, this study demonstrates a convenient method of IPA synthesis.
authors.affiliation: School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China.
authors.forename: Yelin
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Hua
authors.affiliation: School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China.
authors.forename: Biao
authors.initials: B
authors.lastname: Zhang
authors.affiliation: School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China.
authors.forename: Lianhong
authors.initials: L
authors.lastname: Sun
authors.affiliation: School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China.
authors.forename: Wenjie
authors.initials: W
authors.lastname: Li
authors.affiliation: School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China.
authors.forename: Xin
authors.initials: X
authors.lastname: Kong
authors.affiliation: School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, People's Republic of China. hjiong@ustc.edu.cn.
authors.forename: Jiong
authors.identifier: http://orcid.org/0000-0002-4592-7083
authors.initials: J
authors.lastname: Hong
mesh_terms: D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D007211:Indoles / Q000378:metabolism*; D060847:Metabolic Engineering / Q000379:methods; D051279:Tryptophan Transaminase / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D007211:Indoles; C008122:indol-3-yl pyruvic acid; D051279:Tryptophan Transaminase
keywords: Aminotransferase; Indole pyruvic acid; tdiD; tnaA