Complex-type N -glycan recognition by potent broadly neutralizing HIV antibodies

Abstract

Broadly neutralizing HIV antibodies (bNAbs) can recognize carbohydrate-dependent epitopes on gp120. In contrast to previously characterized glycan-dependent bNAbs that recognize high-mannose N -glycans, PGT121 binds complex-type N -glycans in glycan microarrays. We isolated the B-cell clone encoding PGT121, which segregates into PGT121-like and 10-1074–like groups distinguished by sequence, binding affinity, carbohydrate recognition, and neutralizing activity. Group 10-1074 exhibits remarkable potency and breadth but no detectable binding to protein-free glycans. Crystal structures of unliganded PGT121, 10-1074, and their likely germ-line precursor reveal that differential carbohydrate recognition maps to a cleft between complementarity determining region (CDR)H2 and CDRH3. This cleft was occupied by a complex-type N -glycan in a “liganded” PGT121 structure. Swapping glycan contact residues between PGT121 and 10-1074 confirmed their importance for neutralization. Although PGT121 binds complex-type N -glycans, PGT121 recognized high-mannose-only HIV envelopes in isolation and on virions. As HIV envelopes exhibit varying proportions of high-mannose- and complex-type N -glycans, these results suggest promiscuous carbohydrate interactions, an advantageous adaptation ensuring neutralization of all viruses within a given strain.

Identification and specificity of broadly neutralizing antibodies against HIV

“…cDNA was generated from each well and heavy‐ and light‐chain pairs cloned, recombinantly expressed and then screened for neutralization activity. Similar approaches with different baits were used to isolated additional gp120‐specific bnAbs including 3BNC117, 3BNC60,40 and 10‐1074 41. In this method, selection is based purely on the ability to bind the Env bait, and many non‐neutralizing mAbs may also be cloned unless there is counter selection with an epitope‐specific knockout probe.…”

“…22, 71 As per the apex bnAbs, we identified this class by screening single B‐cell cultures, which led to the isolation of the PGT121/4, PGT128, and PGT135 families from three individual donors 22. Later epitope‐focused binding‐based screens yielded similar bnAbs 26, 27, 41. These bnAbs were shown to compete with 2G12, to lose binding activity upon EndoH deglycosylation22 and to bind to the N332 glycan and a gp120 protein epitope including the sequence GDIR 22, 27, 72.…”

Antibody‐virus co‐evolution in HIV infection: paths for HIV vaccine development

“…While the V3-glycan epitope centers on the glycan at N332, high-mannose glycans at other positions can variably be involved in the bnAb epitope (46–49). Such diversity is reflected in crystal and electron microscopy structures by different angles of approaches of individual V3-glycan bnAbs (24, 28,45,46,48–50) (Wilson and Ward, this volume). The V3-glycan bnAb class is of interest for vaccine development because it does not require extensive somatic hypermutation to develop neutralization breadth.…”

Broad Neutralizing Antibodies to HIV Env and Other Complex Viral Antigens from Vaccinated Cows

“…The substitution of aromatic residues, mainly Trp or tyrosine (Tyr), in MPER binding antibodies reduces the neutralization activity of these antibodies [74,84]. Also, the importance of Cys and aromatic residues such as Trp is shown in neutralization activity of CD4bs BrNAbs antibodies [85,86], highlighting the significant function of these residues in either directly in the antigen binding interaction or involvement in shaping the required structure for epitope binding.…”