Fig. 5: Cryo-EM analysis of stabilized RSV-A preF-Δfoldon.

a, Schematic overview of RSV F protein in green, fusion peptide (FP) in orange, HR1 in blue, loop 460–476 in salmon and HR2 in purple. The soluble F ectodomain used in experiments consists of residues 1–524 and lacks the transmembrane (TM) and cytoplasmic (CT) regions. b, Structure of the stabilized trimer, with two monomers shown as surface representation (grey) and one monomer as ribbons with colours according to a, and side chains of stabilizing substitutions shown as cyan spheres. Letters C–H refer to the view of panels c–h relative to b. c, Docking site shown in transparent surface of fusion peptide (orange) with yellow dotted lines showing the interactions of R339 with F137 and substitution 354L (cyan) stabilizing the turn in the fusion peptide. Grey spheres are shown for interacting residues F137, G139 and L142. d, Top view of the neutralized charged ring around the trimeric symmetry axis. e, Side view of the top HR2 with intraprotomeric hydrophobic interactions of L487 (cyan). f,g, Top view around the trimeric symmetry axis (f) and side view (g) of the aromatic cluster showing interactions of both observed 489Y rotamers (cyan). Two different densities were observed for Y489, interacting either with F140 or with both F140 and F137, the N-terminal residue of the fusion peptide. Van der Waals surfaces are shown for the other aromatics. h, Side view (left) of the stabilized HR2 stem and top views (right) with the top layer showing the stabilizing W505 residues (cyan), the middle layer showing the stabilizing F509 residues (cyan) and the bottom layer with L512.