Supersite of immune vulnerability on the glycosylated face of HIV-1 envelope glycoprotein gp120

Abstract

A substantial fraction of broadly neutralizing antibodies (bnAbs) in certain HIV-infected donors recognizes glycan-dependent epitopes on HIV-1 gp120. Here, we elucidate how bnAb PGT 135 recognizes its Asn332 glycan-dependent epitope from its crystal structure with gp120, CD4 and Fab 17b at 3.1 Å resolution. PGT 135 interacts with glycans at Asn332, Asn392 and Asn386, using long CDR loops H1 and H3 to penetrate the glycan shield to access the gp120 protein surface. Electron microscopy reveals PGT 135 can accommodate the conformational and chemical diversity of gp120 glycans by altering its angle of engagement. The combined structural studies of PGT 135, PGT 128 and 2G12 show this Asn332-dependent epitope is highly accessible and much more extensive than initially appreciated, allowing for multiple binding modes and varied angles of approach, thereby representing a supersite of vulnerability for antibody neutralization.

Identification and specificity of broadly neutralizing antibodies against HIV

“…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. By comparing structural information generated for different families within this class, it was shown that the N332/GDIR epitope is accessed from a variety of angles by the different bnAbs, which use diverse binding modes, leading to its definition as a supersite of vulnerability 71. Furthermore, in contrast to some other bnAb classes, these high‐mannose patch bnAbs use a variety of V, D, and J germline genes and do not appear to share particular genetic traits required for binding this epitope 22, 71.…”

“…By comparing structural information generated for different families within this class, it was shown that the N332/GDIR epitope is accessed from a variety of angles by the different bnAbs, which use diverse binding modes, leading to its definition as a supersite of vulnerability 71. Furthermore, in contrast to some other bnAb classes, these high‐mannose patch bnAbs use a variety of V, D, and J germline genes and do not appear to share particular genetic traits required for binding this epitope 22, 71. Thus, it would be difficult to use an NGS approach to identify bnAbs from new donors even if the serum neutralization was clearly N332 dependent.…”

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.…”

“…MacLeod and colleagues isolated a V3-glycan bnAb lineage (the PCDN lineage ) with moderate neutralization breadth and potency (20). PCDN neutralization was sensitive to the H330A mutation (50, 59), depended more on the presence of glycans at positions N156, N301 and N332 and less on integrity of the GDIR motif; it also appeared to require interactions with hybrid glycans (20). …”