The spike (S) protein of SARS-CoV-2 mediates receptor binding and cell entry and is the dominant target of the immune system. It exhibits substantial conformational flexibility. It transitions from closed to open conformations to expose its receptor-binding site and, subsequently, from prefusion to postfusion conformations to mediate fusion of viral and cellular membranes. S-protein derivatives are components of vaccine candidates and diagnostic assays, as well as tools for research into the biology and immunology of SARS-CoV-2. Here we have designed mutations in S that allow the production of thermostable, disulfide-bonded S-protein trimers that are trapped in the closed, prefusion state. Structures of the disulfide-stabilized and non-disulfide-stabilized proteins reveal distinct closed and locked conformations of the S trimer. We demonstrate that the designed, thermostable, closed S trimer can be used in serological assays. This protein has potential applications as a reagent for serology, virology and as an immunogen.

SARS-CoV-2 的刺突 (S) 蛋白介导受体结合和细胞进入，是免疫系统的主要目标。它表现出巨大的构象灵活性。它从封闭构象转变为开放构象以暴露其受体结合位点，随后从融合前构象转变为融合后构象以介导病毒和细胞膜的融合。S-蛋白衍生物是候选疫苗和诊断检测的组成部分，也是 SARS-CoV-2 生物学和免疫学研究的工具。在这里，我们设计了 S 突变，允许产生热稳定的二硫键 S 蛋白三聚体，这些三聚体被困在闭合的融合前状态。二硫键稳定的和非二硫键稳定的蛋白质的结构揭示了 S 三聚体独特的闭合和锁定构象。我们证明了设计的热稳定性封闭 S 三聚体可用于血清学测定。该蛋白质具有作为血清学、病毒学试剂和免疫原的潜在应用。