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Cryo-EM structure of the SARS coronavirus spike glycoprotein in complex with its host cell receptor ACE2

Fig 4

Structure of the disassociated S1-ACE2 complex.

(A) Size-exclusion chromatography profiles of ACE2 alone (blue), cleaved S (green) and the low pH and trypsin treated S and ACE2 mixture. (B) SDS-page analysis of the uncleaved S, cleaved S, S-ACE2, S1-ACE2 and ACE2 peak fractions in “A”. (C) 2D analysis of the S1-ACE2 peak in “A”. Upper: 2D projections of the ACE2 density map calculated from the atomic model (PDB ID: 2ajf). Middle: 2D class averaged images of the particles from the S1-ACE2 peak in “A”. Bottom: components of the complex marked in the 2D class averaged images. ACE2 and S1 densities are marked cyan and pink, respectively. (D) A 3D density map calculated from the particles of the S1-ACE2 peak. The CTD1, CTD2 (pink) and ACE2 (green) are fitted into the density map as a rigid body. The flexible NTD and CTD3 are not visible and are represented as an ellipse. (E) Ribbon diagrams showing the linker downstream the S1/S2 cleavage site and the S2’ cleavage site of ACE2-bound conformation 3 in S1 associated state (left) and S1 disassociated state (right), respectively. The S2’ cleavage site is colored red and indicated by a red arrow. The fusion peptide down-stream of the S2’ site is colored green and the “C” shape loop up-stream the S2’ site is colored blue. The S1 subunit and the linker down-stream the S1/S2 cleavage site of the adjacent protomer is colored cyan and pink, respectively. The black arrow indicates the flexibility of the linker after the disassociation of the S1 subunit.

Fig 4