Cryo-EM structures of HKU2 and SADS-CoV spike glycoproteins and insights into coronavirus evolution

Jinfang Yu; Shuyuan Qiao; Runyu Guo; Xinquan Wang

135 Data collection and refinement statistics for these two structures are listed in Overall structures of HKU2 and SADS-CoV spikes 139 The overall structures of HKU2 and SADS-CoV spikes we determined here resemble 140 the previously reported pre-fusion structures of coronaviruses spikes. Both spike 141 trimers have a mushroom-like shape (~150 Å in height and ~115 Å in width) (Fig. 1a) , 142 consisting of a cap mainly formed by β-sheets of the S1 subunit, a central stalk mainly 143 formed by α-helices of the S2 subunit, and a root formed by twisted β-sheets and loops 144 of the S2 subunit (Fig. 1a) . In each trimer there is a C3 axis along the central stalk ( Fig. 145 1a). The amino acid identity between HKU2 and SADS-CoV spikes is 86%, and these 146 two spike structures are quite similar with the root mean square deviation (r.m.s.d.) 147 being 0.53 Å for 962 aligned Cα atoms of the monomer and 0.56 Å for 2886 aligned 148 Cα atoms of the trimer. Due to the high structural similarity, we will use the HKU2 149 structure to present the features of both spikes in the subsequent description, whereas 150 significant differences between them will be pointed out only when necessary.