Synthesis of L-threo-2,3-dihydroxyphenylserine (L-threo-DOFS) by thermostable L-threonine aldolase expressed in Corynebacterium glutamicum R

In order to examine efficient L-threo-3,4-dihydroxyphenylserine (L-threo-DOFS) synthesis process using whole cell biocatalyst, a thermostable L-threonine aldolase (L-TA), which cloned from Streptomyces coelicolor A3(2) and improved for stability, was expressed in a Corynebacterium glutamicum R strain. The constructed Corynebacterium expression vector, pCG-H44(1) successfully expressed L-TA in C. glutamicum R strain, but showed very low expression level. In order to improve the expression level, the expression vector named pCG-H44(2) was reconstructed by eliminating 1 nucleotide between SD sequence and start codon of L-TA. The pCG-H44(2) vector plasmid was able to overexpress L-TA approximately 3.2 times higher than pCG-H44(1) in C. glutamicum R strain (CGH-2). When the whole cell of CGH-2 was examined in a repeated batch system, L-threo-DOPS was successfully synthesized with a yield of 4.0 mg/ml and maintain synthesis rate constantly after 30 repeated batch reactions for 130 h.