Figure 4.

(a) Structure of a monomer of the ectodomain of the prefusion structure of the NiV F protein shown as a cartoon. The adaptive amino acid 207 is shown as red spheres. Amino acid differences between viruses of the two lineages are depicted as green spheres. The fusion peptide (FP) is shown as orange sticks. DI, DII and DIII are the individual domains. HRB: heptad repeat B. TMR denotes the position of the transmembrane region, which is not present in the crystal structure. (b) Location of residue 42 near the fusion peptide in the trimeric structure of F. R109 is the protease cleavage site, the last residue of the F2 subunit. (c) Post‐fusion structure of Newcastle Disease virus F protein with the adaptive amino acid 207 and the amino acid differences between viruses of the two lineages as green spheres. Note that parts of the DII domain underwent large conformational changes that led to the formation of the heptad repeat region A (HRA) that forms with HRB a six‐helix bundle that is characteristic for the post‐fusion conformation of type I viral fusion proteins [Colour figure can be viewed at http://www.wileyonlinelibrary.com/]