원문정보
초록
영어
Stability-enhanced mutants, H44, l1-94, 5A2-84 and F8, of L-threonine aldolase (L-TA) from Streptomyces coelicolor A3(2) (SCO1085) were isolated by an error-prone PCR followed by a high-throughput screening. Each of these mutants had a single amino acid substitution: H177Y in the H44 mutant, A169T in the l1-94 mutant, D104N in the 5A2-84 mutant and F18I in the F8 mutant. The residual L-TA activity of the wild-type L-TA after a heat treatment for 20 min at 60°C was only 10.6%. However, those in the stability-enhanced mutants were 85.7% for the H44 mutant, 58.6% for the F8 mutant, 62.1% for the 5A2-84 mutant and 67.6% for the l1-94 mutant. Although the half-life of the wild-type L-TA at 63°C was 1.3 min, those of the mutant L-TAs were longer: 14.6 min for the H44 mutant, 3.7 min for the l1-94 mutant, 5.8 min for the 5A2-84 mutant and 5.0 min for the F8 mutant. The specific activity did not change in most of the mutants, but it was decreased by 45% in the case of mutant F8. The most thermostable H44 mutant maintained its L-threo-DOPS synthesizing activity during the 20 repeated batch reactions for 100 h, yielding 4.0 mg/ml of L-threo-DOPS