Synthesis of S-adenosyl-L-methionine in Escherichia coli

Abstract S-adenosyl-L-methionine (SAM) is an important physiological metabolite in vivo and may be useful in medicines. SAM is produced from L-methionine and ATP catalyzed by S-adenosyl-L-methionine synthetase (SAMS) in vivo. In this study, the gene encoding SAMS was cloned and a genetically engineered Escherichia coli (E. coli) BL21(pET-28a-SAMS) was constructed. The recombinant SAMS with a molecular mass of approximately 46 kDa was expressed by inducing the engineered E. coli using isopropyl-s-D-1-thiogalactopyranoside (IPTG) as an inducer. To produce SAM using a low-cost, nontoxic and highperformance expression system, lactose was used as a substitute for IPTG to induce BL21(pET-28a-SAMS). By optimizing the expression conditions, the concentration of SAM produced by the engineered E. coli was 48 mg/L in the culture medium supernatant. To increase the concentration of SAM produced, a coupled system was constructed consisting of E. coli BL21(pET-28a-SAMS) and Saccharomyces cerevisiae (S. cerevisiae) JM-310. In this coupled system, ATP generated from S. cerevisiae was provided to E. coli for producing a higher concentration of SAM. The SAM concentration in the coupled system reached 1.7 g/L. SAM was purified by a weak acid cationic exchange resin D113, and a simple and economical purification procedure for SAM isolation was achieved. SAM was confirmed by High Performance Liquid Chromatography-tandem Mass Spectrometry analysis. Our study provides a feasible and convenient approach to produce SAM.