Guan Jian, Bywaters Stephanie M, Brendle Sarah A, Lee Hyunwook, Ashley Robert E, Christensen Neil D, Hafenstein Susan
Department of Medicine, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
Department of Pathology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
J Virol. 2015 Dec;89(23):12108-17. doi: 10.1128/JVI.02020-15. Epub 2015 Sep 23.
The human papillomavirus (HPV) major structural protein L1 composes capsomers that are linked together through interactions mediated by the L1 C terminus to constitute a T=7 icosahedral capsid. H16.U4 is a type-specific monoclonal antibody recognizing a conformation-dependent neutralizing epitope of HPV thought to include the L1 protein C terminus. The structure of human papillomavirus 16 (HPV16) complexed with H16.U4 fragments of antibody (Fab) was solved by cryo-electron microscopy (cryo-EM) image reconstruction. Atomic structures of virus and Fab were fitted into the corresponding cryo-EM densities to identify the antigenic epitope. The antibody footprint mapped predominately to the L1 C-terminal arm with an additional contact point on the side of the capsomer. This footprint describes an epitope that is presented capsid-wide. However, although the H16.U4 epitope suggests the presence of 360 potential binding sites exposed in the capsid valley between each capsomer, H16.U4 Fab bound only to epitopes located around the icosahedral five-fold vertex of the capsid. Thus, the binding characteristics of H16.U4 defined in this study showed a distinctive selectivity for local conformation-dependent interactions with specific L1 invading arms between five-fold related capsomers.
Human papillomavirus 16 (HPV16) is the most prevalent oncogenic genotype in HPV-associated anogenital and oral cancers. Here we use cryo-EM reconstruction techniques to solve the structures of the HPV16 capsid complexes using H16.U4 fragment of antibody (Fab). Different from most other antibodies directed against surface loops, H16.U4 monoclonal antibody is unique in targeting the C-terminal arm of the L1 protein. This monoclonal antibody (MAb) is used throughout the HPV research community in HPV serological and vaccine development and to define mechanisms of HPV uptake. The unique binding mode of H16.U4 defined here shows important conformation-dependent interactions within the HPV16 capsid. By targeting an important structural and conformational epitope, H16.U4 may identify subtle conformational changes in different maturation stages of the HPV capsid and provide a key probe to analyze the mechanisms of HPV uptake during the early stages of virus infection. Our analyses precisely define important conformational epitopes on HPV16 capsids that are key targets for successful HPV prophylactic vaccines.
人乳头瘤病毒（HPV）主要结构蛋白L1组成壳粒，这些壳粒通过L1 C末端介导的相互作用连接在一起，构成T = 7二十面体衣壳。H16.U4是一种型特异性单克隆抗体，可识别HPV的构象依赖性中和表位，该表位被认为包含L1蛋白C末端。通过冷冻电子显微镜（cryo-EM）图像重建解析了与人乳头瘤病毒16型（HPV16）与抗体（Fab）的H16.U4片段复合的结构。将病毒和Fab的原子结构拟合到相应的冷冻电镜密度中以鉴定抗原表位。抗体足迹主要映射到L1 C末端臂，在壳粒侧面有一个额外的接触点。该足迹描述了一个在整个衣壳中呈现的表位。然而，尽管H16.U4表位表明在每个壳粒之间的衣壳谷中有360个潜在的结合位点暴露，但H16.U4 Fab仅与位于衣壳二十面体五重顶点周围的表位结合。因此，本研究中定义的H16.U4的结合特征显示出对与五重相关壳粒之间特定L1侵入臂的局部构象依赖性相互作用具有独特的选择性。
人乳头瘤病毒16型（HPV16）是HPV相关的肛门生殖器和口腔癌中最普遍的致癌基因型。在这里，我们使用冷冻电镜重建技术来解析使用抗体（Fab）的H16.U4片段的HPV16衣壳复合物的结构。与大多数针对表面环的其他抗体不同，H16.U4单克隆抗体在靶向L1蛋白的C末端臂方面是独特的。这种单克隆抗体（MAb）在HPV研究界广泛用于HPV血清学和疫苗开发以及确定HPV摄取机制。这里定义的H16.U4的独特结合模式显示了HPV16衣壳内重要的构象依赖性相互作用。通过靶向一个重要的结构和构象表位，H16.U4可以识别HPV衣壳不同成熟阶段的细微构象变化，并提供一个关键探针来分析病毒感染早期HPV摄取的机制。我们的分析精确地定义了HPV16衣壳上重要的构象表位，这些表位是成功的HPV预防性疫苗的关键靶点。
