Fig. 3: VHH 4C03 binds a quaternary epitope on preF centered between two adjacent protomers.

a Cryo-EM map of 4C03 and 4C06 bound to preF shown in top-down and side views. 4C03 is colored orange, 4C06 is colored yellow, and each protomer of preF is colored a shade of blue. b Side view of preF with one bound 4C03 VHH shown. The preF trimer is shown as partially transparent surface, colored as in a. 4C03 is shown in light peach with the CDRs colored orange. c (center) The quaternary epitope of 4C03 outlined on a surface representation of preF. PreF is colored gray and the epitope footprint is outlined in orange. Residues within the epitope footprint are colored according to domain within preF as in Fig. 1a. DI is colored light green, DIII is colored light blue, HRC is colored purple. (left) Zoomed-in view of the 4C03 interface with protomer B, shown as cartoons. Select regions of the model have been omitted for clarity. Important residue contacts are shown as sticks with oxygen atoms colored red and nitrogen atoms colored blue. The adjacent protomer (protomer A) is shown as transparent surface, colored by domain. (right) Zoomed-in view of the 4C03 interface with protomer A, shown as cartoons. Select regions of the model have been omitted for clarity. Important residue contacts are shown as in (left), with hydrogen bonds and salt bridges shown as blue dashes.