Impacts on the structure-function relationship of SARS-CoV-2 spike by B.1.1.7 mutations
The UK variant of the severe acute respiratory syndrome coronavirus (SARS-CoV-2), known as B.1.1.7, harbors several point mutations and deletions on the spike (s) protein, which potentially alter its structural epitopes to evade host immunity while enhancing host receptor binding. Here we report the cryo-EM structures of the S protein of B.1.1.7 in its apo form and in the receptor ACE2-bound form. One or two of the three receptor binding domains (RBDs) were in the open conformation but no fully closed form was observed. In the ACE-bound form, all three RBDs were engaged in receptor binding. The B.1.1.7-specific A570D mutation introduced a salt bridge switch that could modulate the opening and closing of the RBD. Furthermore, the N501Y mutation in the RBD introduced a favorable {pi}-{pi} interaction manifested in enhanced ACE2 binding affinity. The N501Y mutation abolished the neutralization activity of one of the three potent neutralizing antibodies (nAbs). Cryo-EM showed that the cocktail of other two nAbs simultaneously bound to all three RBDs. Furthermore, the nAb cocktail synergistically neutralized different SARS-CoV-2 pseudovirus strains, including the B.1.1.7.