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![[Figure 1]](ql5001fig1mag.jpg)
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Figure 1
SARS-CoV-2 spike protein structure and interaction with the ACE2 receptor. (a) Schematic of the full-length spike protein. The S1/S2 furin-cleavage site and the TMPRSS2 S2′ cleavage site are indicated in bold. Residues at the domain boundaries are indicated. NTD, N-terminal domain; RBD, receptor-binding domain; RBM, receptor-binding motif; CTD1/CTD2, carboxy-terminal domains 1 and 2; FP, fusion peptide; HP, heptad repeat; CH, central helix; TM, transmembrane helix; CT, C-terminal tail. (b) Spike-protein structures illustrating the conformational changes that are required for receptor binding and cell entry. The closed state of the spike trimer with three RBDs down (PDB entry 6vxx; Walls et al., 2020  ) is incompatible with receptor binding. The closed spike conformation is in equilibrium with the open state, with one or several RBDs up (PDB entry 6vsb; Wrapp et al., 2020). ACE2 can be bound by RBDs in the up position (PDB entry 7a94; Benton et al., 2020). ACE2 binding facilitates S2′ cleavage, dissociation of S1 and a drastic conformational change to the post-fusion state of S2. The post-fusion state comprises a long three-stranded coiled coil which brings the fusion peptide close to the host cell membrane, facilitating membrane fusion and viral entry (PDB entry 6xra; Cai et al., 2020). |
![[Figure 1]](ql5001fig1.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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