Several fast-spreading variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have become the dominant circulating strains in the COVID-19 pandemic. We report here cryo–electron microscopy structures of the full-length spike (S) trimers of the B.1.1.7 and B.1.351 variants, as well as their biochemical and antigenic properties. Amino acid substitutions in the B.1.1.7 protein increase both the accessibility of its receptor binding domain and the binding affinity for receptor angiotensin-converting enzyme 2 (ACE2). The enhanced receptor engagement may account for the increased transmissibility. The B.1.351 variant has evolved to reshape antigenic surfaces of the major neutralizing sites on the S protein, making it resistant to some potent neutralizing antibodies. These findings provide structural details on how SARS-CoV-2 has evolved to enhance viral fitness and immune evasion.

严重急性呼吸系统综合症冠状病毒 2 (SARS-CoV-2) 的几种快速传播变体已成为 COVID-19 大流行中的主要循环毒株。我们在此报告 B.1.1.7 和 B.1.351 变体的全长刺突 (S) 三聚体的冷冻电子显微镜结构，以及它们的生化和抗原特性。B.1.1.7 蛋白中的氨基酸取代增加了其受体结合域的可及性和受体血管紧张素转换酶 2 (ACE2) 的结合亲和力。增强的受体参与可能是提高传递率的原因。B.1.351 变体已经进化为重塑 S 蛋白上主要中和位点的抗原表面，使其对某些有效的中和抗体具有抗性。