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

Jinfang Yu; Shuyuan Qiao; Runyu Guo; Xinquan Wang

The CTD of δ-coronavirus PdCoV have a core of two β-sheets, belonging to the 256 two-layer CTD subtype (Fig. 3c) . As for the γ-coronavirus IBV, the core of its CTD is 257 also similar to the typical two-layer CTD (Fig. 3c) . However, several β strands are The SD1 and SD2 are two subdomains following the CTD in the S1 subunit, linking 264 the CTD to the S2 subunit. The HKU2 SD1 is a partial β barrel consisting of five β 265 strands and a disulfide bond (C 409 -C 458 ) connecting its C-terminus to the β1 strand ( Fig. 266 4a). This five-stranded β barrel and the linking disulfide bond are conserved among all 267 four genera of coronavirus (Fig. 4a) . The HKU2 SD2 has a structure of two layers of 268 β-sheet with an additional short α-helix over the top sheet (Fig. 4b) . The additional α-269 helix and the top sheet is linked by a disulfide bond (C 482 -C 509 ), and another disulfide 270 bond (C 524 -C 533 ) links the C-terminal loop to the bottom sheet (Fig. 4b) . The two-layer 271 core structure and the second disulfide bond are conserved among all genera of 272 coronavirus, however, the additional α helix and the first linking disulfide bond is a 273 author/funder. All rights reserved. No reuse allowed without permission.