The Effects of Somatic Hypermutation on Neutralization and Binding in the PGT121 Family of Broadly Neutralizing HIV Antibodies
Figure 6
Role of somatic hypermutation in neutralization and antibody structure.
(A) Residues from heavy chain intermediates and light chain intermediates were reverted to germline while indel and CDR3 residues were individually mutated to alanines and tested on a cross-clade virus panel. Highlighted in blue are residues that were reverted to germline. Highlighted in orange are residues reverted between intermediates. Filled red dots represent residues reversions that resulted in significant loss of neutralization as single reversions. Empty red dots represent residue reversions that resulted in significant loss of neutralization as pairwise reversions. Reported fold changes in IC50 are shown in Figure S12. (B) Reported fold changes in IC50 for residues reverted to germline in putative intermediate 3H+3L. (C) Residues that were found to be critical for neutralization in (B) were mapped on a putative PGT121 germline crystal structure. Global structural shifts were observed between germline (gray) and PGT121 (colored). Arrows indicate shifts of CDR loops. (D) 11 Å shift of RL94 in the CDRL3, which was identified to be important for neutralization activity. (E) Salt bridge between RH100 in the CDRH3 and DL67 in the FRL3 insertion that contributes to structural shifts. (F) Effect of N51D mutation in CDRL2. NL51 is highly conserved among all antibody variants and substitution completely abrogates neutralization. The introduction of two hydrogen bonds between the side chain of NL51 and backbone atoms might facilitate a helix to loop change in CDRL1. (G) A H34Q substitution in CDRL1 contributes to stabilizing the proximal positions of CDRL1 and CDRL2.