单核细胞增多性李斯特菌氨基肽酶Lmo1711体外表达及其酶活分析

Characterization of a recombinant aminopeptidase Lmo1711 from Listeria monocytogenes

摘要:

对单核细胞增多性李斯特菌 (简称单增李斯特菌) lmo1711基因编码的氨基肽酶进行克隆表达与纯化，并研究该重组蛋白的体外酶学特性。首先通过生物信息学分析预测Lmo1711与氨基肽酶家族成员的亲缘关系及关键活性位点的保守性。利用SWISS-MODEL模拟预测该蛋白的空间结构；构建Lmo1711原核表达载体并转化入E. coli Rosetta中，诱导表达重组目的蛋白，并利用镍离子亲和层析方法纯化目的蛋白；以氨基酸-对硝基苯胺偶联物为底物，Lmo1711通过水解底物N端氨基酸残基产生游离对硝基苯胺单体，405 nm处检测吸光值对该产物进行检测从而分析Lmo1711的酶学特性。在此基础上系统研究Lmo1711对不同氨基酸残基底物的催化特异性，及不同金属离子对该酶活性的影响。经原核表达纯化获得49.3 kDa的重组Lmo1711蛋白，与预测分子量一致；生物信息学分析推测Lmo1711属于M29氨基肽酶家族，且存在保守关键氨基酸活性位点 (Glu250、Glu316、His345、Tyr352、His378、Asp380)；酶活分析显示，Lmo1711具有较强的氨基肽酶活性，针对不同底物的结合和催化能力差异较大，对亮氨酸残基的亲和程度最高；Lmo1711氨基肽酶活性具有金属离子依赖性，Co2+、Cd2+、Zn2+等多种金属离子均能显著增强其活性，其中Co2+的激活效应最显著。本试验首次发现并证实，单增李斯特菌Lmo1711属于M29氨基肽酶家族成员，具有较强的催化活性，且对金属离子具有不同程度的依赖性。

Abstract:

We aimed to obtain the recombinant aminopeptidase encoded by Listeria monocytogenes (L. monocytogenes) gene lmo1711, and characterized the enzyme. First, the amino acid sequences of Lmo1711 from L. monocytogenes EGD-e and its homologues in other microbial species were aligned and the putative active sites were analyzed. The putative model of Lmo1711 was constructed through the SWISS-MODEL Workspace. Then, the plasmid pET30a-Lmo1711 was constructed and transformed into E. coli for expression of the recombinant Lmo1711. The his-tagged soluble protein was purified using the nickel-chelated affinity column chromatography. With the amino acid-p-nitroaniline as the substrate, Lmo1711 hydrolyzed the substrate to free p-nitroaniline monomers, whose absorbance measured at 405 nm reflected the aminopeptidase activity. The specificity of Lmo1711 to substrates was then examined by changing various substrates, and the effect of metal ions on the catalytic efficiency of this enzyme was further determined. Based on the bioinformatics data, Lmo1711 is a member of the M29 family aminopeptidases, containing a highly conserved catalytic motif (Glu-Glu-His-Tyr-His-Asp) with typical structure arrangements of the peptidase family. The recombinant Lmo1711 with a size of about 49.3 kDa exhibited aminopeptidase activity and had a selectivity to the substrates, with the highest degree of affinity for leucine-p-nitroaniline. Interestingly, the enzymatic activity of Lmo1711 can be activated by Cd2+, Zn2+, and is strongly stimulated by Co2+. We here, for the first time demonstrate that L. monocytogenes lmo1711 encodes a cobalt-activated aminopeptidase of M29 family.