Dissecting Structural Details of Hepadnavirus Subviral Particles

B型肝炎病毒（HBV）感染是一个全球性的公共卫生问题;然而，目前批准的治疗很少导致完全治愈。B型肝炎表面抗原（HBsAg）是HBV感染的血清学标志物。其特征在于三个跨膜蛋白具有相同的C-末端，在N-末端具有可变的框内延伸。自然地，HBsAg蛋白被掺入病毒包膜中或与来自宿主细胞的脂质膜组装成无基因组和无衣壳的亚病毒颗粒（SVP）。最近，通过阻断SVP的组装和释放的新的治疗方法在快速降低慢性HBV感染患者中的HBsAg水平方面显示出有希望的结果。尽管其潜在的临床相关的应用，有没有结构信息可用于HBsAg，但已提出不同的模型SVP。在这个建议中，我们专注于获得高分辨率的结构的SVPs从不同的模型系统使用冷冻电子显微镜（cryo-EM）。我们将测试中心的假设，即结构组织的变化的SVP将有重要的影响，他们的分泌途径。目的1：确定土拨鼠肝炎病毒（WHV）SVP的结构。WHV感染土拨鼠是研究HBV感染机制的重要实验模型。目的二，我们将从携带者血清和肝癌细胞系中阐明HBV SVP的结构细节。我们将使用抗体来空间标记HBsAg的不同区域。最后，将比较从该提议确定的所有结构，并使用嗜肝DNA病毒表面抗原的详细结构信息构建SVP的完整图片。该项目的成功完成将揭示SVP的新结构信息，并将加深我们对HBV颗粒形态发生的理解，以促进目前寻找HBV感染治愈方法的努力。

Hepatitis B virus (HBV) infection is a global public health concern; however, current approval therapies rarely lead to a complete cure. Hepatitis B surface antigen (HBsAg) is the serological marker for HBV infection. It is characterized by three transmembrane proteins having the same C-termini with variable in-frame extension at the N-terminal ends. Naturally, HBsAg proteins are incorporated in the viral envelope or assembled into genome-free and capsid-free subviral particles (SVPs) with the lipid membrane derived from the host cells. Recently, a new therapeutic approach by blocking assembly and release of SVPs has shown promising results in rapidly reducing HBsAg level in chronic HBV- infected patients. Despite its potential clinically relevant applications, there is no structural information available for HBsAg and yet different models of SVPs have been proposed. In this proposal we focus on obtaining the high resolution structures of SVPs from different model systems using cryo-electron microscope (cryo-EM). We will test the central hypothesis that changes in the structural organizations of SVPs will have important implications on their secretion pathway. In Aim 1, we will determine the structures of SVP from woodchuck hepatitis virus (WHV). Woodchuck infected with WHV is a critical experimental model for studying pathogenesis of HBV infection. In Aim 2, we will elucidate the structural details of HBV SVP from carrier's sera and hepatoma cell line. We will use antibodies to spatially label different regions of HBsAg. Finally, all structures determined from this proposal will be compared and used to build a complete picture of SVP with the detailed structural information of Hepadnavirus surface antigen. Successful completion of the proposed project will reveal new structural information of SVPs and will deepen our understanding of HBV particles morphogenesis to facilitate current efforts in finding a cure for HBV infection.