Fig. 1. Design of soluble site Ø-stabilized RSV F trimers.

Over 100 variants of RSV F containing the T4 fibritin-trimerization domain (foldon) were designed to provide greater stability to antigenic site Ø (table S1). Shown here is the structure of the RSV F trimer in its D25-bound conformation with modeled C-terminal appended foldon. The trimer is displayed with two of the three F₁F₂protomers in molecular surface representation (colored tan and pink), and the third F₁F₂ protomer in ribbon representation. The ribbon is colored gray in regions where it is relatively fixed between pre- and postfusion, while the N- and C-terminal residues that move more than 5 Å between pre- and postfusion conformations are colored blue and green, respectively. Mutations compatible with RSV F expression and initial D25 recognition (table S1), but insufficiently stable to allow purification of RSV F as a homogenous trimer (Table 1), are labeled and shown in stick representation (colored black). Insets show enlargements of stabilizing mutations in stick representation (colored red) for DS, Cav1 and TriC variants, all of which sufficiently stabilize antigenic site Ø to allow purification as a homogeneous trimer (Table 1).