Abstract
(R)- or (S)-2-Hydroxy-4-(methylthio)butanoic acid (HMTBA) is used as a poultry nutritional supplement and to treat renal failure disease. Herein, we report an artificially designed biocatalytic cascade process, which uses l-methionine to synthesize (R)- or (S)-HMTBA. This biocatalysis cascade comprises a basic module and two different extender modules and operates in a modular assembly manner. The basic module responsible for the transformation of l-methionine to α-keto-γ-methylthiobutyric acid (KMTB) is comprised of the l-amino acid deaminase. Two different extender modules responsible for the transformation of KMTB to (R)- or (S)-HMTBA are comprised of the R/S-specific lactate dehydrogenase in combination with the formate dehydrogenase, respectively. Engineered Escherichia coli catalysts, one containing the basic module, the other containing the one of two different extender modules, produced 97.6 g L−1 (R)-HMTBA and 96.4 g L−1 (S)-HMTBA with a yield of 96.9% and 95.8% at the large scale (1 L) using a two-stage strategy in one pot, respectively. Therefore, this biocatalytic process lays the foundation for the industrial-scale conversion of low-cost l-amino acids to corresponding high-value enantiopure chiral 2-hydroxy acids.
Highlights
(R)- or (S)-2-Hydroxy-4-(methylthio)butanoic acid (HMTBA) is used as a poultry nutritional supplement and to treat renal failure disease
Bioprocess. (2019) 6:9 are several drawbacks associated with this process, such as the high energy requirement given the need for high temperature and pressure in the final step, potential environmental hazards, and the use of toxic acrolein, methanethiol, and hydrocyanic acid as materials
The first module is the basic module (BM), in which l-Met is transformed to prochiral keto-γ-methylthiobutyric acid (KMTB)
Summary
(R)- or (S)-2-Hydroxy-4-(methylthio)butanoic acid (HMTBA) is used as a poultry nutritional supplement and to treat renal failure disease. Engineered Escherichia coli catalysts, one containing the basic module, the other containing the one of two different extender modules, produced 97.6 g L−1 (R)-HMTBA and 96.4 g L−1 (S)-HMTBA with a yield of 96.9% and 95.8% at the large scale (1 L) using a two-stage strategy in one pot, respectively This biocatalytic process lays the foundation for the industrialscale conversion of low-cost l-amino acids to corresponding high-value enantiopure chiral 2-hydroxy acids. The cyanohydrin hydrolysis process (Tsuyoshi and Masahiro 2006) is the most notable commercial method for HMTBA production, using acrolein and methanethiol as the raw materials in the presence of an organic amine salt to form 3-methylthio propanal, which reacts with hydrocyanic acid to produce 2-hydroxy4-(methylthio)butanenitrile (HMTBN), followed by hydrolysis of sulfuric acid to HMTBA. The engineered strain PvlAADK104R/A337S produced 63.6 g L−1 of KMTB in 24 h with a conversion rate of 91.4% (Hossain et al 2014); there are no reports on the second step alone
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