FIG. 1.

Structure of the DEN-1 sE trimer. (A) Domain I is in red, domain II is in yellow, and domain III is in blue. The fusion loop (FL) is in orange. A 53-residue “stem” (cyan) links the ectodomain to a two-helix C-terminal transmembrane anchor (TM; white hatching). (B to D) DEN-1 sE trimer, colored as in panel A, shown in a ribbon diagram (B) and as surface representations (C and D). The overall fold resembles that of DEN-2 sE (17). The hydrophobic region of the outer leaflet of the fused viral-endosomal membrane is represented by a green rectangle, with representative lipids shown as space fillers. The presumed location of the stem region is shown by a dashed line (a thicker line indicates segments that are α-helical in the mature virus) (25). (B and C) Shown in an all-atom representation are the six disulfide bonds (green), hydrophobic residues in the fusion loop (orange), and Asn67 (yellow), which is glycosylated. A chloride ion (black sphere) binds on the threefold axis near the exposed fusion loops.