Fig 6. Sequence of events in HPIV3 entry, corresponding to cryo-electron microscopy imaging.

(A) HN (green) and F (dark pink) can be found densely packed on the viral surface (light pink) (Image from Fig 1A). (B) Sialic acid (purple) binding to HN occurs in the presence of a host target membrane (blue) (Image from Fig 3B). (C) Upon triggering of F by HN, F undergoes a large conformational change from a pre-fusion globular structure to an extended structure that crosses both membranes (Image from Fig 4B). (D) After this intermediate state, F folds back onto itself, pulling both membranes towards each other, creating a pore in a process that ultimately results in a merged membrane. Scale bars: (A-D) 50 nm.