The SARS-CoV-2 spike is the primary target of virus-neutralizing antibodies and critical to the development of effective vaccines against COVID-19. Here, we demonstrate that the prefusion-stabilized two-proline "S2P" spike-widely employed for laboratory work and clinical studies-unfolds when stored at 4 °C, physiological pH, as observed by electron microscopy (EM) and differential scanning calorimetry, but that its trimeric, native-like conformation can be reacquired by low pH treatment. When stored for approximately 1 week, this unfolding does not significantly alter antigenic characteristics; however, longer storage diminishes antibody binding, and month-old spike elicits virtually no neutralization in mice despite inducing high ELISA-binding titers. Cryo-EM structures reveal the folded fraction of spike to decrease with aging; however, its structure remains largely similar, although with varying mobility of the receptor-binding domain. Thus, the SARS-CoV-2 spike is susceptible to unfolding, which affects immunogenicity, highlighting the need to monitor its integrity.

中文翻译：

---

SARS-CoV-2 S2P 会随着免疫原性改变而经历不同的状态。


SARS-CoV-2 刺突是病毒中和抗体的主要目标，对于开发有效的 COVID-19 疫苗至关重要。在这里，我们证明了广泛用于实验室工作和临床研究的预融合稳定的二脯氨酸“S2P”尖峰，当储存在 4°C、生理 pH 值时会展开，如通过电子显微镜 (EM) 和差示扫描量热法观察到的，但其三聚体、类似天然的构象可以通过低 pH 处理重新获得。当储存大约 1 周时，这种展开不会显着改变抗原特性；然而，较长时间的储存会减少抗体结合，并且尽管诱导了高 ELISA 结合滴度，但一个月大的刺突几乎不会在小鼠中引起中和。冷冻电镜结构揭示了尖峰的折叠部分随着老化而减少；然而，尽管受体结合域的移动性有所不同，但其结构仍然大致相似。因此，SARS-CoV-2 刺突很容易展开，从而影响免疫原性，凸显了监测其完整性的必要性。