猪链球菌2型四川人源分离株ZYH24细胞外蛋白因子的原核表达及活性分析

目的：克隆、表达猪链球菌2型四川人源分离株ZYH24细胞外蛋白因子基因片段，分析蛋白活性。方法：根据GenBank S.suis 2 epf基因序列设计引物，克隆ZYH24株epf基因片段并进行序列分析；构建原核表达质粒pGEX4T-2-epf，在大肠杆菌中诱导带有谷胱苷肽转移酶（GST）标签的融合蛋白EF-GST的表达；亲和层析法纯化融合蛋白EF-GST，用凝血酶切除重组蛋白中的GST，获得纯化的EF抗原；SDS-PAGE和Western blot分析诱导表达及纯化的重组蛋白。结果：序列分析表明，获得的epf基因片段长895bp；原核表达的融合蛋白EF-GST分子量约62000，凝血酶处理后的EF抗原分子量约35000，两者均可与制备的EF多克隆抗血清发生特异性反应。结论：成功克隆了人源分离株ZYH24 epf基因片段，在原核系统实现高效的功能性表达，为开展EF蛋白的相关研究奠定了基础。

Prokaryotic expression and activity detection of truncated extracellular protein factor gene of human Streptococcus suis type 2

Objective:To clone and express the truncated epf gene of Streptococcus suis type 2(S.suis 2) strain ZYH24 isolated from a patient in Ziyang County, Sichuan province, and detect its activity.Methods:The epf gene fragment was amplified by PCR from ZYH24 and cloned into prokaryotic expression plasmid pGEX4T-2 to form pGEX4T-2-epf. The expression of recombinant protein with glutathione S-transferase(GST) was induced in E.coli TG1 and the fusion protein(EF-GST) was purified by affinity chromatography, and then GST was cut from EF-GST with thrombin protease. The expressed and purified proteins were analyzed by SDS-PAGE and confirmed by Western blot.Results:Sequence analysis showed that the length of the truncated epf was 859 bp. The prokaryotic expressed production was a fusion protein, whose molecular weight was about 62 000,and the molecular weight of the purified EF protein was about 35 000. Western blot analysis showed that EF-GST and EF were detected specifically by EF antiserum.Conclusion:The truncated epf gene of human S.suis 2 strain ZYH24 has been successfully cloned, and the high expression of the functional recombinant protein is achieved in the prokaryotic system in E.coli TG1 induced by IPTG. The expression protein is one of the functional parts of EF, which facilitates the further studies on the bio-function and immunology.