Fig. 4.

A fusion-active extended intermediate of the S2 central stalk. (a-c) Views of docked three ACE2 dimers onto the extended stalk. The viral membrane is shown in small circles, and the middle plane of the host membrane is shown in ellipses around each ACE2 dimer. They are approximately parallel to one another. The top end of the EMD-9597 is close to the middle plane of the host membrane. (a) Same view as (h) of Fig. S2. (b) 60° rotated view. (c) Host end view. See Fig. S2 for piecewise assembly. See Figs. S2 and S3 for conformational changes of spike subunit and trimer during the prefusion to post-fusion conversion, and Video 3A, 3B, and 3C for motions of ACE2 for continued opening of the central pore of the spike trimer and for resulting the post-fusion S2 in super-complexes.