Figure 1. Structural analysis of 3BC176/3BC315 paratopes, and their epitopes on the BG505 SOSIP.664_293F trimer.

(a) X-ray structures of 3BC176 and 3BC315 are shown in cartoon rendering. The Fab heavy chain (HC) and light chain (LC) are shown in dark and light grey, respectively. The CDR loops are coloured and labelled. (b) Cα superimposition of the 3BC176 and 3BC315 Fab variable regions. 3BC315 is shown in orange (HC) and yellow (LC) and 3BC176 in green. (c) Single-particle cryo-EM reconstruction of 3BC315 Fab in complex with the BG505 SOSIP.664_293F trimer. Only two Fabs are bound per trimer. The map has been segmented in Chimera into gp120 (light grey), gp41 (dark grey) and Fab (blue) using coordinates from PDB ID: 4TVP for the SOSIP Env trimer and the Fab structure as determined here. The scale bar corresponds to 50 Å. (d) Three copies of gp140 and two copies of 3BC315 Fab structures were fit independently into the EM map (white surface). The gp120 and gp41 are shown as light and dark grey ribbons, respectively. Fab LC and HC are coloured in orange and blue. The small protruding bumps on the Env surface correspond to glycans.