Spike (S) glycoprotein of SARS-CoV2 exists chiefly in two conformations, open and closed. Most previous structural studies on S protein have been conducted at pH 8.0, but knowledge of the conformational propensities under both physiological and endosomal pH conditions is important to inform vaccine development. Our current study employed single-particle cryoelectron microscopy to visualize multiple states of open and closed conformations of S protein at physiological pH 7.4 and near-physiological pH 6.5 and pH 8.0. Propensities of open and closed conformations were found to differ with pH changes, whereby around 68% of S protein exists in open conformation at pH 7.4. Furthermore, we noticed a continuous movement in the N-terminal domain, receptor-binding domain (RBD), S2 domain, and stalk domain of S protein conformations at various pH values. Several key residues involving RBD-neutralizing epitopes are differentially exposed in each conformation. This study will assist in developing novel therapeutic measures against SARS-CoV2.

SARS-CoV2 的刺突 (S) 糖蛋白主要以开放和封闭两种构象存在。大多数以前的 S 蛋白结构研究都是在 pH 8.0 下进行的，但了解生理和内体 pH 条件下的构象倾向对于疫苗开发非常重要。我们目前的研究采用单粒子冷冻电子显微镜来观察 S 蛋白在生理 pH 7.4 和近生理 pH 6.5 和 pH 8.0 下的多种开放和闭合构象状态。发现开放和封闭构象的倾向随 pH 变化而不同，其中约 68% 的 S 蛋白在 pH 7.4 时以开放构象存在。此外，我们注意到在不同 pH 值下，S 蛋白构象的 N 端结构域、受体结合结构域 (RBD)、S2 结构域和茎结构域不断移动。涉及 RBD 中和表位的几个关键残基在每个构象中有差异地暴露。这项研究将有助于开发针对 SARS-CoV2 的新型治疗措施。