Synthetic glycopeptides reveal the glycan specificity of HIV-neutralizing antibodies

A new class of glycan-reactive HIV-neutralizing antibodies, including PG9 and PG16, has been recently discovered that appear to recognize novel glycopeptide epitopes on HIV-1 gp120. However, further characterization and reconstitution of the precise neutralizing epitopes are complicated by the heterogeneity of glycosylation. We report here the design, synthesis, and antigenic evaluation of novel cyclic V1V2 glycopeptides carrying defined N-linked glycans at the conserved glycosylation sites (N160 and N156/N173) derived from gp120 of two HIV-1 isolates. Antibody binding studies confirmed the necessity of a Man(5)GlcNAc(2) glycan at N160 for recognition by PG9 and PG16, and further revealed a critical role of a sialylated N-glycan at the secondary site (N156/N173) in the context of glycopeptides for antibody binding. In addition to defining the glycan specificities of PG9 and PG16, the identified synthetic glycopeptides provide a valuable template for HIV-1 vaccine design.