Networks of HIV-1 Envelope Glycans Maintain Antibody Epitopes in the Face of Glycan Additions and Deletions

Abstract

Summary Numerous broadly neutralizing antibodies (bnAbs) have been identified that target the glycans of the HIV-1 envelope spike. Neutralization breadth is notable given that glycan processing can be substantially influenced by the presence or absence of neighboring glycans. Here, using a stabilized recombinant envelope trimer, we investigate the degree to which mutations in the glycan network surrounding an epitope impact the fine glycan processing of antibody targets. Using cryo-electron microscopy and site-specific glycan analysis, we reveal the importance of glycans in the formation of the 2G12 bnAb epitope and show that the epitope is only subtly impacted by variations in the glycan network. In contrast, we show that the PG9 and PG16 glycan-based epitopes at the trimer apex are dependent on the presence of the highly conserved surrounding glycans. Glycan networks underpin the conservation of bnAb epitopes and are an important parameter in immunogen design.

Glycan Positioning Impacts HIV-1 Env Glycan-Shield Density, Function, and Recognition by Antibodies

“…The loss of key glycans may produce a hole in the shield that renders it more vulnerable to neutralization by BnAbs, but where that hole emerges is also difficult to predict. Our results confirm a cluster of glycans proximal to N262 that we and others have previously proposed ( Hargett et al., 2019 ; Lemmin et al., 2017 ; Seabright et al., 2020 ). Our analyzed Env variants and mutants represent nearly half of all NGS combinations in the sequences deposited in the LANL HIV database for this N262-cluster of glycans and can serve as a model system to study how glycans affect Env structure and function.…”

“…Molecular-dynamic simulations enabled visualization of the complex changes induced by specific oligosaccharide positions and indicated that some glycans are able to move to compensate for a loss of a glycan and that glycan density (number of glycans within a region/microdomain) plays a functional role in the Env structure. These results confirm the interdependent nature of an NGS subset in the high-mannose patch that have been proposed to work as a microdomain of glycans ( Hargett et al., 2019 ; Lemmin et al., 2017 ; Seabright et al., 2020 ). Together, these complementary applications of molecular biology, modeling, and functional glycomics revealed how individual glycans of the massive Env glycan shield can alter the Env glycan processing and, consequently, Env function.…”

Virus-Receptor Interactions of Glycosylated SARS-CoV-2 Spike and Human ACE2 Receptor

“…Nonetheless, it has been proposed that this virus, and others, acquires a glycan coat sufficient and similar enough to endogenous host protein glycosylation that it serves as a glycan shield, facilitating immune evasion by masking non-self viral peptides with self-glycans (15,(20)(21)(22). In parallel with their potential masking functions, glycan-dependent epitopes can elicit specific, even neutralizing, antibody responses, as has been described for HIV-1 ( (15,(25)(26)(27)(28)(29), https://www.biorxiv.org/content/10.1101/2020.06.30.178897v1). Thus, understanding the glycosylation of the viral Spike trimer is fundamental for the development of efficacious vaccines, neutralizing antibodies, and therapeutic inhibitors of infection.…”

Mass Spectrometry-Based Structural Virology

“… 115 , 129 Furthermore, neutralizing antibodies targeting glycans at various specific glycosites, within and outside these oligomannose patches, have also been described. 115 , 127 , 129 , 148 …”

“… 117 Taken together, these integrative structural biology approaches provide much more comprehensive information about, among others, the density of the glycan shields, 116 organization of weakly immunogenic oligo-mannose patches around the protein backbone, 117 , 123 conservation of specific glycans and glycosylation sites, 178 as well as important glycan epitopes and accessibility for broadly neutralizing antibodies. 127 , 128 …”