Gu Ying, Zhang Jun, Wang Ying-Bin, Li Shao-Wei, Yang Hai-Jie, Luo Wen-Xin, Xia Ning-Shao
Key Laboratory of Ministry of Education for Cell Biology and Tumor Cell Engineering, Xiamen University, Xiamen 361005, China.
Sheng Wu Gong Cheng Xue Bao. 2003 Nov;19(6):680-5.
Hepatitis E is an acute hepatitis casused by hepatitis E virus (HEV) in developing countries, where it occurs as cases sporadic and in epidemics form. The causative agent, hepatitis E virus, is transmitted primarily by the fecal-oral route. HEV is icosahedron non-enveloped virus, and its genome is a single-stranded, positive-sense, 3'-polyadenylated RNA about 7.5 kb in length. It contains three open reading frames (ORFs). Of which ORF1 codes for a polyprotein of 1693 amino acids and contain domains homologous to a viral methyltransferase, a papainlike cysteine protease, an RNA helicasre, and an RNA-dependent RNA polymerase, besides the most hypervariable region of the HEV genome. And ORF3 codes for a 123-amino-acide-long polypeptide with unknown function. While the major viral capsid protein (pORF2, ORF2 codes) of 660 amino acid was showed to contain the protective epitope. The bacterially expressed polypeptide disignated as NE2 has been proved to be a protective antige. And the anti-NE2 monoclonal antibodies (mAb) was screend, two of these mAbs 8C11 and 8H3 were showed to be against separate conformational neutralization epitope of hepatitis E virus (HEV). And these two mAb were used to screen for binding peptides from a 7-peptides phage display library. After four rounds of panning, tweenty-one positive monoclonal phages (11 for 8C11, and 10 for 8H3) were selected and the inserted fragments were sequenced. The DNA sequence coding for the obtained dominant peptide 8C11 (N'-His-Pro-Thr-Leu-Leu-Arg-Ile-C', named 8C11A) and 8H3 (N'-Ser-Ile-Leu-Pro-Tyr-Pro-Tyr-C', named 8H3A) were then synthesized and cloned to insert between amino acid 78 to 83 of hepatitis B core antigen (HBcAg), then expressed in E. coli. The recombinant proteins aggregate into homodimer or polymer on SDS-PAGE, and could bind with mAb 8C11 and 8H3 in Western blotting. Respectively, the recombinant protein C8C11A showed to be dimer mainly, which can bind with mAb 8C11. The monomer and dimer of C8H3A are in the same amount on SDS-PAGE, but only the dimer could bind with mAb 8H3 on Western blotting. The renatured recombinant proteins were all showed to aggregate into virus like particles which were similar as HBcAg on transmission electron micrograph. The dominant peptide 8H3A (N'-Ser-Ile-Leu-Pro-Tyr-ProTyr-C') that selected out by mAb 8H3 was further chemo-synthesized, and its binding activity was confirmed by BIAcore biosensor. The result showed that this 7-peptide can bind with mAb 8H3 in a big Ka and Kd form, which means the binding is not stable. These results implicated that conformational dependent neutralization epitope could be partially modeled by short peptide, which provided a feasible route for subunit vaccine development.
戊型肝炎是发展中国家由戊型肝炎病毒(HEV)引起的急性肝炎,以散发病例和流行形式出现。病原体戊型肝炎病毒主要通过粪-口途径传播。HEV是二十面体无包膜病毒,其基因组是一条约7.5kb长的单链、正链、3'-多聚腺苷酸化RNA。它包含三个开放阅读框(ORF)。其中ORF1编码一个1693个氨基酸的多聚蛋白,除了HEV基因组的高变区外,还包含与病毒甲基转移酶、木瓜蛋白酶样半胱氨酸蛋白酶、RNA解旋酶和RNA依赖性RNA聚合酶同源的结构域。ORF3编码一个功能未知的123个氨基酸长的多肽。而660个氨基酸的主要病毒衣壳蛋白(pORF2,由ORF2编码)含有保护性表位。已证明细菌表达的多肽NE2是一种保护性抗原。筛选了抗NE2单克隆抗体(mAb),其中两种mAb 8C11和8H3被证明针对戊型肝炎病毒(HEV)不同的构象中和表位。用这两种mAb从一个7肽噬菌体展示文库中筛选结合肽。经过四轮淘选,选择了21个阳性单克隆噬菌体(8C11的11个,8H3的10个)并对插入片段进行测序。然后合成编码获得的优势肽8C11(N'-His-Pro-Thr-Leu-Leu-Arg-Ile-C',命名为8C11A)和8H3(N'-Ser-Ile-Leu-Pro-Tyr-Pro-Tyr-C',命名为8H3A)的DNA序列,并克隆到乙肝核心抗原(HBcAg)的氨基酸78至83之间,然后在大肠杆菌中表达。重组蛋白在SDS-PAGE上聚合成同二聚体或多聚体,在Western印迹中能与mAb 8C11和8H3结合。重组蛋白C8C11A主要显示为二聚体,能与mAb 8C11结合。C8H3A的单体和二聚体在SDS-PAGE上含量相同,但在Western印迹中只有二聚体能与mAb 8H3结合。复性后的重组蛋白均聚合成病毒样颗粒,在透射电子显微镜下与HBcAg相似。mAb 8H3筛选出的优势肽8H3A(N'-Ser-Ile-Leu-Pro-Tyr-ProTyr-C')进一步化学合成,其结合活性通过BIAcore生物传感器得到证实。结果表明,该7肽能以较大的Ka和Kd形式与mAb 8H3结合,这意味着结合不稳定。这些结果表明,构象依赖性中和表位可以部分地由短肽模拟,这为亚单位疫苗的开发提供了一条可行的途径。