PDF(Pubmed)
Abstract：
The 800 million human infections with SARS-CoV-2 and the likely emergence of new variants and additional coronaviruses necessitate a better understanding of the essential spike glycoprotein and the development of immunogens that foster broader and more durable immunity. The S2 fusion subunit is more conserved in sequence, is essential to function, and would be a desirable immunogen to boost broadly reactive antibodies. It is, however, unstable in structure and in its wild-type form, cannot be expressed alone without irreversible collapse into a six-helix bundle. In addition to the irreversible conformational changes of fusion, biophysical measurements indicate that spike also undergoes a reversible breathing action. However, spike in an open, \"breathing\" conformation has not yet been visualized at high resolution. Here we describe an S2-only antigen, engineered to remain in its relevant, pre-fusion viral surface conformation in the absence of S1. We also describe a panel of natural human antibodies specific for S2 from vaccinated and convalescent individuals. One of these mAbs, from a convalescent individual, afforded a high-resolution cryo-EM structure of the prefusion S2. The structure reveals a complex captured in an \"open\" conformation with greater stabilizing intermolecular interactions at the base and a repositioned fusion peptide. Together, this work provides an antigen for advancement of next-generation \"booster\" immunogens and illuminates the likely breathing adjustments of the coronavirus spike.
摘要：
8亿人感染SARS-CoV-2，以及可能出现的新变体和其他冠状病毒，需要更好地了解必需的尖峰糖蛋白和免疫原的发展，从而促进更广泛和更持久的免疫力。S2融合亚基序列更保守，对功能至关重要，并且将是增强广泛反应性抗体的理想免疫原。是的,然而,结构和野生型形式不稳定，如果不可逆地塌陷成六螺旋束，则不能单独表达。除了融合的不可逆构象变化，生物物理测量表明，尖峰也经历了可逆的呼吸作用。然而,在一个开放的尖峰，“呼吸”构象尚未在高分辨率下可视化。这里我们描述了一种仅S2抗原，被设计成保持其相关性，在不存在S1的情况下，融合前病毒表面构象。我们还描述了一组对来自接种疫苗和恢复期个体的S2具有特异性的天然人抗体。其中一个单克隆抗体，来自一个康复期的人，提供了融合前S2的高分辨率低温EM结构。该结构揭示了以“开放”构象捕获的复合物，在碱基处具有更大的稳定分子间相互作用和重新定位的融合肽。一起,这项工作为下一代“增强剂”免疫原的发展提供了抗原，并阐明了冠状病毒尖峰可能的呼吸调整。
