Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
Institute for Virology, Helmholtz Zentrum Muenchen, Technische Universitaet Muenchen, Neuherberg, Germany.
J Virol. 2018 Jun 29;92(14). doi: 10.1128/JVI.00272-18. Print 2018 Jul 15.
During the morphogenesis of hepatitis B virus (HBV), an enveloped virus, two types of virions are secreted: (i) a minor population of complete virions containing a mature nucleocapsid with the characteristic, partially double-stranded, relaxed circular DNA genome and (ii) a major population containing an empty capsid with no DNA or RNA (empty virions). Secretion of both types of virions requires interactions between the HBV capsid or core protein (HBc) and the viral surface or envelope proteins. We have studied the requirements from both HBc and envelope proteins for empty virion secretion in comparison with those for secretion of complete virions. Substitutions within the N-terminal domain of HBc that block secretion of DNA-containing virions reduced but did not prevent secretion of empty virions. The HBc C-terminal domain was not essential for empty virion secretion. Among the three viral envelope proteins, the smallest, S, alone was sufficient for empty virion secretion at a basal level. The largest protein, L, essential for complete virion secretion, was not required but could stimulate empty virion secretion. Also, substitutions in L that eliminated secretion of complete virions reduced but did not eliminate empty virion secretion. S mutations that blocked secretion of the hepatitis D virus (HDV), an HBV satellite, did not block secretion of either empty or complete HBV virions. Together, these results indicate that both common and distinct signals on empty capsids and mature nucleocapsids interact with the S and L proteins during the formation of complete and empty virions. Hepatitis B virus (HBV) is a major cause of severe liver diseases, including cirrhosis and cancer. In addition to the complete infectious virion particle, which contains an outer envelope layer and an interior capsid that, in turn, encloses a DNA genome, HBV-infected cells also secrete noninfectious, incomplete viral particles in large excess over the number of complete virions. In particular, the empty (or genome-free) virion shares with the complete virion the outer envelope and interior capsid but contains no genome. We have carried out a comparative study on the capsid and envelope requirements for the secretion of these two types of virion particles and uncovered both shared and distinct determinants on the capsid and envelope for their secretion. These results provide new information on HBV morphogenesis and have implications for efforts to develop empty HBV virions as novel biomarkers and a new generation of HBV vaccine.
在乙型肝炎病毒（HBV）的形态发生过程中，会分泌两种类型的病毒粒子：（i）少量完整病毒粒子，包含具有特征性部分双链、松弛环状 DNA 基因组的成熟核衣壳；（ii）大量包含无 DNA 或 RNA（空病毒粒子）的空衣壳。两种类型的病毒粒子的分泌都需要 HBV 衣壳或核心蛋白（HBc）与病毒表面或包膜蛋白之间的相互作用。我们研究了 HBc 和包膜蛋白在完整病毒粒子分泌方面的要求，以及在空病毒粒子分泌方面的要求。HBc N 端结构域内的突变会阻断含 DNA 病毒粒子的分泌，但不会完全阻止空病毒粒子的分泌。HBc C 端结构域对空病毒粒子的分泌不是必需的。在三种病毒包膜蛋白中，最小的 S 蛋白单独就足以在基础水平上分泌空病毒粒子。对完整病毒粒子分泌至关重要的最大蛋白 L 虽然不是必需的，但可以刺激空病毒粒子的分泌。此外，消除完整病毒粒子分泌的 L 蛋白突变会减少但不会消除空病毒粒子的分泌。阻断乙型肝炎 delta 病毒（HDV）分泌的 S 蛋白突变不会阻断空或完整 HBV 病毒粒子的分泌。这些结果表明，在形成完整和空病毒粒子的过程中，空衣壳和成熟核衣壳上的共同和独特信号都与 S 和 L 蛋白相互作用。乙型肝炎病毒（HBV）是导致严重肝脏疾病的主要原因，包括肝硬化和癌症。除了含有外包膜层和内部衣壳的完整感染性病毒粒子外，HBV 感染细胞还会大量分泌非感染性、不完整的病毒粒子，其数量超过完整病毒粒子的数量。特别是，空（或无基因组）病毒粒子与完整病毒粒子共享外包膜和内部衣壳，但不含基因组。我们对这两种类型的病毒粒子分泌所需的衣壳和包膜进行了比较研究，揭示了衣壳和包膜上用于其分泌的共同和独特决定因素。这些结果为 HBV 形态发生提供了新信息，并为开发空 HBV 病毒粒子作为新型生物标志物和新一代 HBV 疫苗的努力提供了依据。
