A systematic study of the N-glycosylation sites of HIV-1 envelope protein on infectivity and antibody-mediated neutralization

Background: Glycans on the human immunodeficiency virus (HIV) envelope glycoprotein (Env) play an important role in viral infection and evasion of neutralization by antibodies. In this study, all 25 potential N-linked glycosylation sites (PNGS) on the HIV-1 CRF07_BC Env, FE, were mutated individually to study the effect of their removal on viral infectivity, virion production, and antibody-mediated neutralization. Results: Removal of specific N-glycosylation sites has a significant effect on viral infectivity and antibody-mediated neutralization phenotype. Six of these glycosylation mutants located on the V1/V2 and C1/C2 domains lost infectivity. PNGS mutations located on V4/C4/V5 (except N392 on V4), were shown to increase viral infectivity. Furthermore, FE is much more dependent on specific glycans than clade B Env YU-2. On neutralization effect, PNGS mutations at N197 (C2), N301 (V3), N442 (C4) and N625 (gp41) rendered the virus more susceptible to neutralization by the monoclonal antibodies (MAbs) that recognize the CD4 binding site or gp41. Generally, mutations on V4/V5 loops, C2/C3/C4 regions and gp41 reduced the neutralization sensitivity to PG16. However, mutation of N289 (C2) made the virus more sensitive to both PG9 and PG16. Furthermore, we showed that mutations at N142 (V1), N355 (C3) and N463 (V5) conferred resistance to neutralization by anti-gp41 MAbs. We used the available structural information of HIV Env and homology modeling to provide a structural basis for the observed biological effects of these mutations. Conclusions: This report provides the first systematic experimental account of the biological role of the entire PNGS on an HIV-1 Env, which should provide valuable insights for understanding the function of Env in HIV infection cycle and for developing future anti-HIV strategies.