Cryo-EM structure of infectious bronchitis coronavirus spike protein reveals structural and functional evolution of coronavirus spike proteins
(A) Schematic drawing of IBV S1. SD1: subdomain 1. SD2: subdomain 2. SD1’ and SD1”: two parts of SD1. SD2’ and SD2”: two parts of SD2. (B) Structure of monomeric S1. S1-NTD is colored in cyan. S1-CTD is colored in green. SD1 is colored in magenta. SD2 is colored in orange. * indicates putative sugar-binding site. Partial ceiling on top of the S1-NTD core is labeled. Putative receptor-binding motif loops (RBMs) in S1-CTD are also labeled. (C) Structure of trimeric S1. Three S1 subunits are colored differently. (D) Structure of monomeric S2. The structural elements are colored in the same way as in Fig 1A. (E) Structure of trimeric S2. Dotted line indicates residues 702–710 that are missing in the structural model. The structural elements of subunit A are colored in the same way as in Fig 1D. Subunits B and C are colored in light purple and light pink, respectively. All structures are viewed from the side.