Cryo-EM structure of N751-2C09.01 in complex with BG505 DS-SOSIP reveals epitope similarity to N751-2C06.01
To understand the differences and similarities between antibodies 2C06 and 2C09, we determined the cryo-EM structure of 2C09 in complex with BG505 DS-SOSIP. 2C09 binding to the envelope trimer did not induce noticeable asymmetry, and we obtained a 3D-reconstruction map at 2.81 Å with C3 symmetry from 445,733 particles (The fusion peptide in the 2C09 bound complex also formed a U-shape conformation, except for its two N-terminal residues (512 and 513), which turned back to interact with antibody. As a result, fusion-peptide binding to 2C09 involved residues 512–520 interacting almost exclusively with heavy-chain CDRs (The heavy chain of 2C09 contributed about 70% of the total epitope surface. The CDR H3 of 2C09 was four residues shorter than that of 2C06 and, unlike in the 2C06-Env complex, did not reach the neighboring gp41; this difference accounted for most of the difference in total BSA (