Johnson Adam, Dodes Traian Martín, Walsh Richard M, Jenni Simon, Harrison Stephen C
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
Laboratory of Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA.
J Virol. 2025 Feb 25;99(2):e0180924. doi: 10.1128/jvi.01809-24. Epub 2024 Dec 31.
Flavivirus envelope (E) and precursor M (prM) proteins, when ectopically expressed, assemble into empty, virus-like particles (VLPs). Cleavage of prM to M and loss of the pr fragment converts the VLPs from immature to mature particles, mimicking a similar maturation of authentic virions. Most of the VLPs obtained by prM-E expression are smaller than virions; early, low-resolution cryo-EM studies suggested a simple, 60-subunit, icosahedral organization. We describe here the cryo-EM structure of immature, small VLPs (smVLPs) from dengue virus type 2 and show that they have octahedral rather than icosahedral symmetry. The asymmetric unit of the octahedral particle is an asymmetric trimer of prM-E heterodimers, just as it is on icosahedral immature virions; the full, octahedrally symmetric particle thus has 24 such asymmetric trimers or 72 prM-E heterodimers in all. Cleavage of prM and release of pr generates ovoid, somewhat irregular, mature particles. Previous work has shown that mature smVLPs have fusion properties identical to those of virions, consistent with local, virion-like clustering of 36 E dimers on their surface. The cryo-EM structure and the properties of the smVLPs described here relate directly to ongoing efforts to use them as vaccine immunogens.
Ectopic expression of flavivirus envelope (E) and precursor M (prM) proteins leads to the formation and secretion of empty, virus-like particles (VLPs). We show that a major class of VLPs, of smaller diameter than those of virion size ("small VLPs": smVLPs), are octahedrally symmetric particles. The known characteristics of immature virions (asymmetric trimers of prM-E heterodimers) allow us to understand the assembly of an octahedral (rather than icosahedral) surface lattice. Cleavage of prM and formation of mature, fusogenic smVLPs yield somewhat irregular, ovoid particles. These observations are directly relevant to proposals for using immunogenic but non-infectious VLPs as components of specific flavivirus vaccines.
黄病毒包膜（E）蛋白和前体M（prM）蛋白异位表达时，会组装成空的病毒样颗粒（VLP）。prM裂解为M并丢失pr片段会使VLP从不成熟颗粒转变为成熟颗粒，模拟了真实病毒粒子的类似成熟过程。通过prM-E表达获得的大多数VLP比病毒粒子小；早期的低分辨率冷冻电镜研究表明其具有简单的60亚基二十面体结构。我们在此描述了2型登革病毒未成熟小VLP（smVLP）的冷冻电镜结构，结果显示它们具有八面体而非二十面体对称性。八面体颗粒的不对称单元是prM-E异二聚体的不对称三聚体，就像在二十面体未成熟病毒粒子上一样；因此，完全的八面体对称颗粒总共具有24个这样的不对称三聚体或72个prM-E异二聚体。prM的裂解和pr的释放产生了卵形、 somewhat不规则的成熟颗粒。先前的研究表明，成熟的smVLP具有与病毒粒子相同的融合特性，这与它们表面36个E二聚体的局部病毒粒子样聚集一致。这里描述的smVLP的冷冻电镜结构和特性直接关系到目前将它们用作疫苗免疫原的研究工作。
黄病毒包膜（E）蛋白和前体M（prM）蛋白的异位表达导致空的病毒样颗粒（VLP）的形成和分泌。我们表明，一类主要的VLP，其直径比病毒粒子小（“小VLP”：smVLP），是八面体对称颗粒。未成熟病毒粒子（prM-E异二聚体的不对称三聚体）的已知特征使我们能够理解八面体（而非二十面体）表面晶格的组装。prM的裂解和成熟的、具有融合性的smVLP的形成产生了 somewhat不规则的卵形颗粒。这些观察结果与使用具有免疫原性但无感染性的VLP作为特定黄病毒疫苗成分的提议直接相关。
