School of Cancer Sciences, The University of Birmingham, Edgbaston, Birmingham, United Kingdom.
J Virol. 2012 Sep;86(18):9606-16. doi: 10.1128/JVI.00559-12. Epub 2012 Jun 27.
Hepatitis C virus (HCV) causes chronic liver disease, cirrhosis, and primary liver cancer. Despite 130 million people being at risk worldwide, no vaccine exists, and effective therapy is limited by drug resistance, toxicity, and high costs. The tetraspanin CD81 is an essential entry-level receptor required for HCV infection of hepatocytes and represents a critical target for intervention. In this study, we report the first structural characterization of the large extracellular loop of CD81, expressed in mammalian cells and studied in physiological solutions. The HCV E2 glycoprotein recognizes CD81 through a dynamic loop on the helical bundle, which was shown by nuclear magnetic resonance (NMR) spectroscopy to adopt a conformation distinct from that seen in crystals. A novel membrane binding interface was revealed adjacent to the exposed HCV interaction site in the extracellular loop of CD81. The binding pockets for two proposed inhibitors of the CD81-HCV interaction, namely, benzyl salicylate and fexofenadine, were shown to overlap the HCV and membrane interaction sites. Although the dynamic loop region targeted by these compounds presents challenges for structure-based design, the NMR assignments enable realistic screening and validation of ligands. Together, these data provide an improved avenue for developing potent agents that specifically block CD81-HCV interaction and also pave a way for elucidating the recognition mechanisms of diverse tetraspanins.
丙型肝炎病毒（HCV）可导致慢性肝病、肝硬化和原发性肝癌。尽管全世界有 1.3 亿人面临风险，但目前仍没有疫苗，而有效的治疗方法受到耐药性、毒性和高成本的限制。四跨膜蛋白 CD81 是 HCV 感染肝细胞所必需的入门受体，是干预的关键靶点。在这项研究中，我们报告了首次对哺乳动物细胞中表达的 CD81 的大细胞外环进行的结构特征描述，并在生理溶液中进行了研究。HCV E2 糖蛋白通过螺旋束上的动态环识别 CD81，这一点通过核磁共振（NMR）光谱学得到证实，其构象与晶体中观察到的构象不同。在 CD81 细胞外环的暴露 HCV 相互作用位点旁边揭示了一个新的膜结合界面。两个拟议的 CD81-HCV 相互作用抑制剂（即苯甲酸钠和非索非那定）的结合口袋被证明与 HCV 和膜相互作用位点重叠。尽管这些化合物靶向的动态环区域给基于结构的设计带来了挑战，但 NMR 分配使配体的现实筛选和验证成为可能。这些数据共同为开发专门阻断 CD81-HCV 相互作用的有效药物提供了一条更好的途径，并为阐明不同四跨膜蛋白的识别机制铺平了道路。
