Figure 2.

Conformational change of HA during pH-induced membrane fusion. Different intermediates states of HA during pH-induced conformational change were identified by cryo-EM [60]. The top and side views of state 1 (prefusion conformation, PDB 6Y5H) [60], state 2 (dilated form 1, PDB 6Y5I) [60], state 3 (dilated form 2, PDB 6Y5J) [60], state 4 (extended HA2, PDB 6Y5K) [60], and state 5 (post-fusion conformation, PDB 1QU1) are shown [61]. Of note, after fusion peptide is released from state 2, the fusion peptide becomes disordered [60]. In state 3, the membrane proximal region (yellow) is also disordered [60]. Different components in the HA2 that are involved in structural rearrangements between pre- and post-fusion structures are in different colors.