FIG 6.

SCIV-induced V2-directed cross-neutralizing antibodies bind occluded-open but not closed trimers. (A) 2D class averages of NSEM images showing Fabs (arrows) bound to single Env protomers. Fabs (denoted on top) were generated for members of the most cross-reactive antibody lineage from RM T927 (P3G11 and P1B05) and RM T925 (P1A12), respectively (also see Fig. 5). Although both ZM197-ZM233 and CAM13K SOSIP preparations were used, only Fab-monomer complexes were observed. (B) 3D reconstructions of Fab-monomer complexes, shown in two orthogonal views, with the Env domain in gray and the Fab in color (P1B05, purple; P3G11, green; P1A12, gold). The scale bar indicates 20 Å. (C) Volume rendering of the PG9 Fab (tan, PDB 3U2S) in complex with a prefusion BG505 trimer (PDB 5FYL), of which only a single protomer (gray) is shown. The Env densities in panel B were aligned with the Env density in panel C and are shown in the same orientation. The black cylinder denotes the position of the 3-fold trimer axis. (D) 2D class averages showing Fabs (arrows) bound to SOSIP trimers lacking the N156 glycan (CH505_N156Q SOSIP). (E) 3D reconstructions of Fabs bound to CH505_N156Q SOSIP trimers. Both side (upper) and top (lower) views are shown, with the Fabs highlighted in color as in panel B. The densities of the CH505_N156Q SOSIP are consistent with an occluded-open trimer. The scale bar indicates 20 Å. (F) Volume rendering of PG9 (tan, PDB 3U2S) in complex with a closed, prefusion BG505 trimer (PDB 5FYL), shown in the same orientation as in panel E. The black cylinder indicates the central 3-fold axis of the Env trimer.