Production of enantiopure (R)- or (S)-2-hydroxy-4-(methylthio)butanoic acid by multi-enzyme cascades

(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 alpha-keto-gamma-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 industrialscale conversion of low-cost l-amino acids to corresponding high-value enantiopure chiral 2-hydroxy acids.