Pseudomonas putida KT2440低特异性L-苏氨酸醛缩酶的表达、酶学性质及温度稳定性提高
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国家自然科学基金(31370100);江苏省六大人才高峰高层次人才资助项目(2015-SWYY-010);高等学校学科创新引智计划资助(111-2-06)


Expression, characterization and thermostability improvement of low-specificity L-threonine aldolase from Pseudomonas putida KT2440
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    摘要:

    [目的]从Pseudomonas putida KT2440基因组中,钓取低特异性L-苏氨酸醛缩酶基因(ltaE),构建重组大肠杆菌。研究目标酶的酶学性质,和关键氨基酸位点突变对酶活和温度稳定性的影响。[方法]以P.putida KT2440基因组DNA为模板,PCR扩增出ltaE基因,构建重组表达质粒pET28a-KT2440并转化Escherichia coli BL21(DE3),获得重组菌E.coli BL21(DE3)/pET-KT2440,利用Ni2+柱亲和层析纯化低特异性L-苏氨酸醛缩酶(LTA),对关键氨基酸位点Thr206和Lys207实施定点突变。[结果]SDS-PAGE结果表明LTA在大肠杆菌中获得高效表达,分子量为40 kDa左右,与理论值大小相符。Ni2+柱亲和层析纯化LTA,获得单一条带。利用双酶耦联法测得LTA酶活为5577.3 U/mg,最适反应温度为50℃,最适pH为8.0。在温度低于45℃,pH 5.0-9.0时,重组酶较稳定。LTA酶的Kmkcat值为23.95 mmol/L和19216.6 s-1。Mg2+、Ca2+金属离子对LTA有明显的促进作用,而Ni2+、Cu2+、Zn2+、Fe2+等对酶有明显的抑制作用。该酶在叔丁基甲基醚溶剂中具有良好的耐受性,在叔丁基甲基醚中保存1 h后仍保留90%以上的酶活。Thr206Ser突变明显提高了酶对温度的稳定性。Lys207对酶催化功能是必需的,该位点突变对酶活都是致死的。[结论]克隆并表达P.putida KT2440的LTA酶,研究了酶学性质,通过定点改造提高了酶的温度稳定性,筛选获得一种酶耐受性好的有机溶剂,为LTA酶在有机溶剂中高效稳定催化β-羟基-α-氨基酸奠定了较坚实的研究基础。

    Abstract:

    [Objective] To construct a recombinant Escherichia coli BL21 (DE3)/pET-KT2440, a low-specificity L-threonine aldolase gene (ltaE) was cloned from the genome of Pseudomonas putida KT2440. The enzyme characterization and the effects of key amino acid mutations on the enzyme activity and thermo-stability were investigated.[Methods] The ltaE gene was amplified by PCR with the genome of P. putida KT2440 as template. The recombinant plasmid pET28a-KT2440 was constructed and transformed into E. coli BL21 (DE3). The low-specificity L-threonine aldolase (LTA) was purified by Ni2+ affinity chromatography and then was characterized. The key amino acids Thr206 and lys207 were mutated by site-directed mutagenesis. [Results] SDS-PAGE analysis showed that LTA were highly expressed in E. coli BL21 (DE3) with a molecular weight of about 40 kDa, consistent with the theoretical value. A single band was observed through Ni2+ affinity chromatography. LTA had a specific activity of 5577 U/mg by two coupled-enzyme assay method. The optimal temperature and pH were 50℃ and 8.0, respectively, and was stable below 40℃ and pH between 5.0 and 9.0. LTA exhibited Km and kcat values of 23.95 mmol/L and 19216.6 s-1 under the optimal conditions. Mg2+ and Ca2+ obviously stimulated enzyme activity, whereas Ni2+, Cu2+, Zn2+ and Fe2+ obviously inhibited it. LTA enzyme presented good resistance in tert-butyl methyl ether. The residual activity was retained over 90% after pre-incubation of the enzyme in TBME for 1 h. Site-directed mutation indicated that Thr206Ser significantly increased the thermal stability. Lys207 is essential for enzymatic function. Any mutation of K207 was lethal for enzyme activity. [Conclusion] The thermostability was improved by site-directed mutation. The work provides a solid foundation for the efficient and stable biosynthesis of β-hydroxy-α-amino acids by LTA.

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李利宏,张荣珍,周丽仙,柳志永,旋凯昂,饶俊超,徐岩. Pseudomonas putida KT2440低特异性L-苏氨酸醛缩酶的表达、酶学性质及温度稳定性提高[J]. 微生物学报, 2019, 59(10): 2013-2023

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  • 收稿日期:2018-12-05
  • 最后修改日期:2019-03-15
  • 在线发布日期: 2019-10-10
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