Figure 4. Stalk/head domain interface in the PIV5-HN ectodomain structure.

A) Cartoon rendering with transparent surface of the PIV5-HN stalk showing the locations of known category I (affect fusion only) and category II (affect fusion and NA) mutations in NDV and PIV5 HN (adapted from [21] and expanded to include current data). The stalk residues at the stalk/head interface are shown as sticks and labeled. B) Zoomed-in view of the stalk/head interface with individual chains colored as in Fig. 1. Sidechains at the interface are shown as lighter colored sticks. C) A MONSTER contact map of the DOD₁ interface analogous to that in Fig. 3B. PIV5 residues at the stalk/head interface that align with residues present in the NDV stalk/head interface are highlighted with an asterisk. Red asterisks mark identical residues across both interfaces. D) Overlay of the head domains of a covalent dimer of NDV HN (yellow) with PIV5 HN (green and orange) showing the different angles of the stalks relative to the heads in the two structures.