Complex-type <i>N</i> -glycan recognition by potent broadly neutralizing HIV antibodies

TLDR

Broadly neutralizing HIV antibodies recognize carbohydrate‑dependent epitopes on gp120, and unlike most glycan‑dependent bNAbs that target high‑mannose N‑glycans, PGT121 binds complex‑type N‑glycans. We isolated the B‑cell clone encoding PGT121, revealing distinct PGT121‑like and 10‑1074‑like groups with differing sequence, binding affinity, carbohydrate recognition, and neutralizing activity; structural analysis showed that carbohydrate recognition maps to a cleft between CDRH2 and CDRH3, occupied by a complex‑type N‑glycan in PGT121, and swapping glycan contact residues confirmed their importance for neutralization; although PGT121 binds complex‑type N‑glycans, it recognizes high‑mannose‑only envelopes, indicating promiscuous carbohydrate interactions that enable neutralization across envelope glycan heterogeneity.

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.