Erro-prone PCR에 의해서 열안정성이 향상된 Streptomyces coelicolor A(3) 유래의 L-threonine aldolase를 Corynebacterium glutamicum R에서 과잉발현시키기 위하여 Corynebacterium용 vector plasmid인 pCRB1의 SD배열과 개시코든사이의 1염기를 제거한 고발현용 vector plasmid인 pCG-H44(2)를 구축하였다. pCG-H (2)에 의해서 형질전환된 C. glutamicum R 균주(CGH44-2)에서 L-TA를 발현시킨 결과, 기존의 Corynebacterium용 vector plasmid인 pCRB1(CGH44-1)보다 L-TA의 발현량이 높았다. L-threo-DOPS의 합성을 위한 최적조건은 $30^{circ}C$, 0.1 M cirtric acid buffer(pH 7.0)이었으며, 0.1% TritonX-100를 첨가하였을 경우 보다 높은 활성을 보였다. 최적조건하에서 CGH44-2를 whole cell biocatalyst로 이용한 반복회분식반응에서 재조합대장균을 숙주로 이용한 경우보다 재조합Corynebacterium을 이용하였을 경우, 목적하는 L-threo-DOPS의 합성이 안정적으로 이루어졌다.
In order to examine efficient L-threo-2,3-Dihydroxyphenylserine (L-threo-DOPS) 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.
