Fig. 2

Distinguishing features of BG505 NFL.664. a Features of BG505 NFL.664 that do not appear in the cleaved BG505 SOSIP.664 structure are highlighted. Most of the flexible linker (dark green) is disordered in the crystal structure. The NFL design lacks the disulfide bond (SOS) between residues 501 and 605, and retains the original Ala and Thr at the respective positions in the primary sequence. b The 20-residue HR1_N region forms a helix (red cartoon) with the I559P trimer-stabilizing mutation disrupting it. c The backbone atoms of the FP (residues Ala512 to Gly527) are shown as observed in the BG505 NFL.664 structure. Top inset: FP conformations in the unbound (red on BG505 NFL.664) and bound (dark gray on BG505 SOSIP.664) to VRC34.01 (slate blue, PDB 5I8H) on the BG505 NFL.664 (white) and BG505 SOSIP.664 (wheat), respectively. The HR1_N (green), FPPR, and the flexible linker are labeled for context. Bottom inset: The unbound FP (red) is shown on the BG505 NFL.664 trimer. d Three residues (red) of the 2xG₄S linker are observed in the crystal structure. The insets compare the residue conformations at positions 501 and 605 in JRFL WTΔCT (lacking the SOS mutation like NFL) and SOSIP designs. The 2mF_o−F_c electron density composite omit maps (blue mesh) surrounding these features are contoured at 1.0σ