定点突变技术鉴定弓形虫微线体蛋白6与醛缩酶的作用位点

Protein Interaction Site of Toxoplasma gondii Microneme Protein 6 and Aldolase Determined by Site-directed Mutagenesis

目的利用定点突变技术鉴定弓形虫微线体蛋白6(MIC6)与醛缩酶的作用位点。方法根据GenBank中的弓形虫RH株MIC6基因序列(登录号为AF110270)及C端序列设计特异性引物,将MIC6蛋白羧基端(MIC6C)348位色氨酸(W348)的密码子碱基突变为缬氨酸(V)的碱基,PCR扩增MIC6C W/V突变体基因片段,克隆至原核表达质粒pGEX-4T-1,转化至大肠埃希菌BL21(DE3);0.8 mmol/L异丙基-β-D-硫代半乳糖苷(IPTG)诱导表达GST-MIC6C W/V突变体蛋白,亲和层析法纯化表达产物。以GST-MIC6C W/V突变体蛋白为探针蛋白,GST-MIC6C蛋白为对照蛋白,分别与弓形虫速殖子裂解液进行GST沉降实验,采用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDSPAGE)和蛋白质印迹(Western blotting)分析实验产物。分别以GST-MIC6C W/V突变体蛋白和GST-MIC6C蛋白为探针蛋白和对照蛋白,与弓形虫醛缩酶蛋白液进行GST沉降实验,SDS-PAGE分析实验产物。结果获得了MIC6C W/V突变体基因片段,构建了相应的原核表达载体,表达并纯化了GST-MIC6C W/V突变体蛋白。GST-MIC6C W/V突变体蛋白与弓形虫速殖子裂解液的GST沉降产物中未见蛋白条带,而GST-MIC6C蛋白的沉降产物中可见一蛋白条带,且能被抗醛缩酶抗体特异识别;GST-MIC6C W/V突变体蛋白与弓形虫醛缩酶蛋白液的GST沉降产物中未见蛋白条带,而GST-MIC6C蛋白的沉降产物中可见一蛋白条带。结论色氨酸(W348)为MIC6与醛缩酶的作用位点。

Objective To identify the protein interaction site of Toxoplasma gondii microneme protein 6 （MIC6） and aldolase by using site-directed mutagenesis. Methods Based on Toxoplasma gondii MIC6 gene sequence （GenBank Accession No. AF110270）, the specific primers were designed. Tryptophan（W）-348 of MIC6 C terminus （MIC6C） was mutated to valine（V） via site-directed mutagenesis. MIC6C W/V gene was obtained from cDNA library by PCR amplification and subcloned into pGEX-4T-1. The mutant protein GST-MIC6C W/V was expressed in E. coli, induced by 0.8 mmol/L IPTG, and purified by affinity chromatography. Glutathione sepharose beads were incubated with GST-MIC6C W/V and GST-MIC6C, respectively, and then incubated with T. gondii tachyzoites lysate, and bound proteins were eluted using sample buffer. Bound products were resolved by SDS-PAGE and Western blotting. Glutathione sepharose beads were incubated with GST-MIC6C W/V and GST-MIC6C, respectively, and then incubated with aldolase-His6. After incubation, the resin was washed and subjected to SDS-PAGE. Results The MIC6C W/V gene was obtained, and the recombinant plasmid MIC6C W/V/pGEX-4T-1 was successfully constructed. The mutant protein GST-MIC6C W/V was expressed and purified in vitro. SDS-PAGE analysis indicated that GST-MIC6C was co-precipitated with aldolase from T. gondii tachyzoites lysate or aldolase-His6, whereas GST-MIC6C W/V failed to precipitate aldolase from T. gondii tachyzoites lysate or aldolase-His6. Western blotting analysis using anti-aldolase antibody indicated that GST-MIC6C could pull-down aldolase from T. gondii tachyzoites lysate. Conclusion Tryptophan （W348） was the interaction site of MIC6 and aldolase in T. gondii.