恶性疟原虫环子孢子蛋白肝细胞靶向肽段CSR2 a-EGFP 的原核表达、纯化及鉴定

Expression and purification of r ecombinant circumsporozoite proteins of Plasmodium falciparum and evaluation of their binding activities to hepatocytes

目的：从恶性疟原虫FCC1／HN株环子孢子蛋白（circumsporozoite protein，CSP）的全长编码基因中扩增4个CSP基因编码片段，克隆至原核表达载体pET28 a／EGFP 中进行表达纯化，观察环子孢子蛋白肽段与EGFP融合蛋白对肝细胞的靶向结合能力，探讨其作为原发性肝癌基因治疗的靶向分子载体的可行性。方法根据恶性疟原虫FCC1／HN株环子孢子蛋白的编码序列设计4对引物，利用聚合酶链反应（ PCR ）扩增出4段CSP 的编码基因，将其克隆到原核表达载体pET28 a／EGFP中，与EGFP融合表达，在大肠杆菌BL21中用IPTG诱导表达，表达产物用Ni2＋螯合柱亲和纯化，采用SDS-PAGE对纯化的融合蛋白检测；并观察重组环子孢子蛋白对不同组织细胞的结合能力。结果从恶性疟原虫FCC1／HN株CSP基因中成功扩增到4段分别为300、90、120、80 bp的基因片段，且在原核表达载体pET28 a／EGFP中经诱导表达出相对分子质量约39＆#215;103、31＆#215;103、33＆#215;103和30＆#215;103大小的融合蛋白： CSR1a-EGFP、CSR1b-EGFP、CSR2a-EGFP及CSR2b-EGFP；通过Ni2＋亲和柱纯化获得重组CSP融合蛋白，能被疟原虫阳性血清特异识别，且CSR2 a-EGFP能够与肝癌和正常肝细胞特异性地结合，与其他组织来源的细胞则未见反应。结论重组环子孢子蛋白CSR2a-EGFP能够与肝组织特异性地结合，作为原发性肝癌基因治疗的靶向分子具有一定的潜在应用价值。

Objective To amplify four fragments of circumsporozoite （ CSP） protein gene from Plasmodium falciparum FCC1/HN strain and express recombinant CSP proteins in prokaryotic vector pET28 a/EGFP for further evaluation of their binding activities to hepatic cells .Methods Four pairs of primers were designed according to the cDNA sequence of CSP protein from Plasmodium falciparum FCC1/HN strain and used to amplify the gene fragments by PCR .The cloned gene fragments were inserted into pET28a/EGFP to construct the recombinant expression plasmids .The transformed E.coli BL21 strains carry-ing expression plasmids were induced by IPTG to express CPS proteins .The recombinant CSP proteins were purified with Ni2＋chelating HiTrap HP column and detected by SDS-PAGE.The binding activities of the ex-pressed proteins to different tissues were also detected .Results Four gene fragments encoding CSP protein were successfully amplified and expressed in E.coil BL21 strain as fusion protein CSR1a-EGFP, CSR1b-EGFP, CSR2a-EGFP and CSR2b-EGFP with a relative molecular mass of about 39＆#215;103, 31＆#215;103, 33＆#215;103 and 30 ＆#215;10 3 , respectively .The purified fusion proteins reacted specifically with Plasmodium falciparum-posi-tive serum samples.Moreover, the recombinant protein CSR2a-EGFP could bind to the hepatic cells specif-ically rather than other cells.Conclusion The purified recombinant CSR2a-EGFP protein has a strong binding activity to hepatocytes , indicating its potential value as a targeting molecule for hepatic gene therapy .