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

Jinfang Yu; Shuyuan Qiao; Runyu Guo; Xinquan Wang

The S1 subunit of the HKU2 spike comprises two major domains, NTD and CTD, 152 which are followed by two subdomains SD1 and SD2 connecting them to the S2 subunit 153 ( Fig. 1b and Fig. 1c) . The S1 subunits from three monomers form the cap of the spike, The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.02.23.961912 doi: bioRxiv preprint (Fig. 1a) . The NTD, CTD, SD1 and SD2 of the S1 subunit are all mainly composed of 157 β strands regarding to the secondary structure feature (Fig. 1c) . In contrast, the upstream 158 helix (UH), fusion peptide (FP), connecting region (CR), heptad repeat 1 (HR1) and 159 central helix (CH) of the S2 subunit are mainly composed of helices, whereas the β-160 hairpin (BH) and subdomain 3 (SD3) at the bottom part of the S2 subunit mainly consist 161 of β stands and loops (Fig. 1c) . Moreover, the residues after the SD3, which contain the The SD1 and SD2 of the S1 subunit and the S2 subunit are highly similar in amino The NTD of HKU2 has three layers of antiparallel β-sheet with the top one consisting 182 of six strands, the middle one consisting of five strands and the bottom one consisting 183 of three strands. Below the bottom sheet is a short α-helix (Fig. 2a) . The top and middle 184 β-sheets form a galectin-like β-sandwich fold, which is inserted between two stands of 185 the bottom sheet (Fig. 2a) . To supplement, three disulfide bonds are detected in the 186 author/funder. All rights reserved. No reuse allowed without permission.