Booy F P, Roden R B, Greenstone H L, Schiller J T, Trus B L
Laboratory of Structural Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, 20892, USA.
J Mol Biol. 1998 Aug 7;281(1):95-106. doi: 10.1006/jmbi.1998.1920.
Complexes between bovine papillomavirus type 1 (BPV1) and examples of two sets of neutralizing, monoclonal antibodies (mAb) to the major capsid protein (L1) were analyzed by low-dose cryo-electron microscopy and three-dimensional (3D) image reconstruction to 13 A resolution. mAb #9 is representative of a set of neutralizing antibodies that can inhibit viral binding to the cell surface, while mAb 5B6 is representative of a second set that efficiently neutralizes papillomaviruses without significantly inhibiting viral binding to the cell surface. The 3D reconstructions reveal that mAb #9 binds to L1 molecules of both pentavalent and hexavalent capsomeres. In contrast, 5B6 binds only to hexavalent capsomeres, reflecting the significant structural or environmental differences for the 5B6 epitope in the 12 pentavalent capsomeres. Epitope localization shows that mAb #9 binds monovalently to the tips of capsomeres whereas 5B6 binds both monovalently and bivalently to the sides of hexavalent capsomeres approximately two-thirds of the way down from the outer tips, very close to the putative stabilizing intercapsomere connections. The absence of mAb 5B6 from the pentavalent capsomeres and its inability to prevent viral binding to the cell surface suggest that receptor binding may occur at one or more of the 12 virion vertices.
通过低剂量冷冻电子显微镜和三维（3D）图像重建技术，将分辨率提高到13埃，对1型牛乳头瘤病毒（BPV1）与针对主要衣壳蛋白（L1）的两组中和性单克隆抗体（mAb）的复合物进行了分析。mAb #9代表一组能够抑制病毒与细胞表面结合的中和抗体，而mAb 5B6代表另一组能够有效中和乳头瘤病毒但不会显著抑制病毒与细胞表面结合的抗体。3D重建显示，mAb #9与五价和六价衣壳粒的L1分子结合。相比之下，5B6仅与六价衣壳粒结合，这反映了12个五价衣壳粒中5B6表位存在显著的结构或环境差异。表位定位表明，mAb #9单价结合在衣壳粒的顶端，而5B6单价和双价结合在六价衣壳粒侧面，距离外端约三分之二处，非常接近假定的稳定衣壳粒间连接。五价衣壳粒中不存在mAb 5B6，且其无法阻止病毒与细胞表面结合，这表明受体结合可能发生在12个病毒粒子顶点中的一个或多个处。
