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

Jinfang Yu; Shuyuan Qiao; Runyu Guo; Xinquan Wang

Actually, this is mainly caused by different positioning and interaction between NTD 281 and CTD in the spike monomer. The HKU2 S1 subunit, similar to those in -282 coronaviruses HCoV-NL63, HCoV-226E and PEDV and -coronavirus PdCoV, have 283 an "inward" CTD which contacts with the NTD (Fig. 5a) . The three structural "NTD-284 CTD" modules in the cap region of these spikes are composed of NTD and CTD from 285 the same monomer, forming the intra-subunit packing in the spike trimer (Fig. 5a) . The 286 S1 subunits of other coronaviruses in the and -genera including MHV, SARS-CoV, 287 MERS-CoV, HCoV-OC43 and IBV have an "outward" CTD that is far away from the 288 NTD (Fig. 5b) . Therefore, the three structural "NTD-CTD" modules in the cap region 289 of these spikes have the NTD from one monomer and the CTD from the adjacent 290 monomer, forming the cross-subunit packing in the spike trimer (Fig. 5b) . Interestingly, 291 we found that the "outward" CTDs always have an insertion in the core structure, such 292 as β-coronavirus CTDs and -coronavirus IBV CTD (Fig. 5b) . In contrast, all "inward"