Fig 11.

Schematic representation of fusion activation by NDV site II. See Discussion, describing the use of NDV HN or chimeric HPIV3 HN-NDV HN or NiV G-NDV HN as receptor binding proteins, paired with NDV, HPIV3, or NiV F. Each row depicts a different HN stalk/F pair, as indicated. The NDV HN heads engage sialic acid receptors in the presence of zanamivir (the yellow molecule appearing in the second column). Zanamivir blocks binding by NDV HN′s site I but activates binding site II. Upon engagement of site II, each F inserts its fusion peptide into the target membrane, and fusion ensues.