Wakata Aika, Kanemoto Satoshi, Tang Huamin, Kawabata Akiko, Nishimura Mitsuhiro, Jasirwan Chyntia, Mahmoud Nora Fahmy, Mori Yasuko
Division of Clinical Virology, Center for Infectious Diseases, Kobe University Graduate School of Medicine, Kobe, Japan.
Department of Immunology, Nanjing Medical University, Nanjing, China.
J Virol. 2018 Feb 12;92(5). doi: 10.1128/JVI.02074-17. Print 2018 Mar 1.
Human herpesvirus 6A (HHV-6A) glycoprotein B (gB) is a glycoprotein consisting of 830 amino acids and is essential for the growth of the virus. Previously, we reported that a neutralizing monoclonal antibody (MAb) called 87-y-13 specifically reacts with HHV-6A gB, and we identified its epitope residue at asparagine (Asn) 347 on gB. In this study, we examined whether the epitope recognized by the neutralizing MAb is essential for HHV-6A infection. We constructed HHV-6A bacterial artificial chromosome (BAC) genomes harboring substitutions at Asn347, namely, HHV-6A BACgB(N347K) and HHV-6A BACgB(N347A). These mutant viruses could be reconstituted and propagated in the same manner as the wild type and their revertants, and MAb 87-y-13 could not inhibit infection by either mutant. In a cell-cell fusion assay, Asn at position 347 on gB was found to be nonessential for cell-cell fusion. In addition, in building an HHV-6A gB homology model, we found that the epitope of the neutralizing MAb is located on domain II of gB and is accessible to solvents. These results indicate that Asn at position 347, the linear epitope of the neutralizing MAb, does not affect HHV-6A infectivity. Glycoprotein B (gB) is one of the most conserved glycoproteins among all herpesviruses and is a key factor for virus entry. Therefore, antibodies targeted to gB may neutralize virus entry. Human herpesvirus 6A (HHV-6A) encodes gB, which is translated to a protein of about 830 amino acids (aa). Using a monoclonal antibody (MAb) for HHV-6A gB, which has a neutralizing linear epitope, we analyzed the role of its epitope residue, N347, in HHV-6A infectivity. Interestingly, this gB linear epitope residue, N347, was not essential for HHV-6A growth. By constructing a homology model of HHV-6A gB, we found that N347 was located in the region corresponding to domain II. Therefore, with regard to its neutralizing activity against HHV-6A infection, the epitope on gB might be exposed to solvents, suggesting that it might be a target of the immune system.
人类疱疹病毒6A（HHV - 6A）糖蛋白B（gB）是一种由830个氨基酸组成的糖蛋白，对病毒的生长至关重要。此前，我们报道了一种名为87 - y - 13的中和单克隆抗体（MAb）与HHV - 6A gB特异性反应，并确定其表位残基位于gB上的天冬酰胺（Asn）347处。在本研究中，我们检测了中和单克隆抗体识别的表位对HHV - 6A感染是否至关重要。我们构建了在Asn347处有替换的HHV - 6A细菌人工染色体（BAC）基因组，即HHV - 6A BACgB(N347K)和HHV - 6A BACgB(N347A)。这些突变病毒能够以与野生型及其回复株相同的方式重建和增殖，并且单克隆抗体87 - y - 13不能抑制任何一种突变体的感染。在细胞 - 细胞融合试验中，发现gB上第347位的Asn对细胞 - 细胞融合并非必需。此外，在构建HHV - 6A gB同源模型时，我们发现中和单克隆抗体的表位位于gB的结构域II上且可被溶剂接触。这些结果表明，中和单克隆抗体的线性表位第347位的Asn不影响HHV - 6A的感染性。糖蛋白B（gB）是所有疱疹病毒中最保守的糖蛋白之一，是病毒进入的关键因素。因此，靶向gB的抗体可能中和病毒进入。人类疱疹病毒6A（HHV - 6A）编码gB，其被翻译为一种约830个氨基酸（aa）的蛋白质。使用针对HHV - 6A gB的具有中和线性表位的单克隆抗体，我们分析了其表位残基N347在HHV - 6A感染性中的作用。有趣的是，这个gB线性表位残基N347对HHV - 6A的生长并非必需。通过构建HHV - 6A gB的同源模型，我们发现N347位于对应于结构域II的区域。因此，就其对HHV - 6A感染的中和活性而言，gB上的表位可能暴露于溶剂中，这表明它可能是免疫系统的一个靶点。
