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. 2020 Oct 27;94(22):e01301-20. doi: 10.1128/JVI.01301-20

FIG 2.

FIG 2

Structural evolution of coronavirus spike protein. (A) The architecture of the SADS-CoV S trimer. The three S protomers are shown in different colors (magenta, cyan, and green), and the receptor-binding moieties are colored wheat and indicated with black circles. The black arrows indicate the direction of S1-CTD expansion during the transition from an inactive state to an active state. (B to E) Architectural features of spike protein trimers from the four coronavirus genera. (B) S trimer of the alphacoronavirus HCoV-NL63 (PDB accession number 5SZS); (C) S trimer of the deltacoronavirus PdCoV (PDB accession number 6BFU); (D) S trimer of the gammacoronavirus infectious bronchitis virus (IBV) (PDB accession number 6CV0); (E) S trimer of the betacoronavirus SARS-CoV (PDB accession number 5X58). (F) Structure of the SADS-CoV S protomer. The red frame indicates the linker between CTD and SD1. NTD, CTD, and the receptor-binding moiety are labeled and indicated by black arrows. (G to O) Structural characteristics of spike protein S1-NTDs from the four coronavirus genera. The NTD core and subdomain (dotted rectangle) are labeled. A partial ceiling or ceiling is indicated with a black arrow, and the sugar-binding site or putative sugar-binding site is indicated by a red star. (G to I) Subtype I alphacoronavirus S1-NTDs. (G) SADS-CoV S1-NTD; (H) HCoV-NL63 S1-NTD1 (PDB accession number 5SZS); (I) FCoV S1-NTD1 (PDB accession number 6JX7). (J) S1-NTD of the gammacoronavirus IBV (PDB accession number 6CV0). (K) S1-NTD of the betacoronavirus SARS-CoV (PDB accession number 5X58). (L to N) Subtype II alphacoronavirus NTDs. (L) HCoV-NL63 S1-NTD2 (PDB accession number 5SZS); (M) FCoV S1-NTD1 (PDB accession number 6JX7); (N) HCoV-229E S1-NTD (PDB accession number 6U7H). (O) S1-NTD of the deltacoronavirus PdCoV (PDB accession number 6BFU). (P to T) Structural characteristics of the spike protein S1-CTDs from the four coronavirus genera. The RBM loops or putative RBM loops are indicated by dotted circles, whereas the extended RBM loops and RBM subdomain are indicated by black arrows. (P and Q) One-layer S1-CTDs. (P) SADS-CoV S1-CTD; (Q) S1-CTD of the betacoronavirus SARS-CoV (PDB accession number 5X58). (R to T) Two-layer S1-CTDs. (R) S1-CTD of the alphacoronavirus HCoV-NL63 (PDB accession number 5SZS); (S) S1-CTD of the deltacoronavirus PdCoV (PDB accession number 6BFU); (T) S1-CTD of the gammacoronavirus IBV (PDB accession number 6CV0).