Removal of N-Linked Glycosylation Sites in the V1 Region of Simian Immunodeficiency Virus gp120 Results in Redirection of B-Cell Responses to V3

Abstract

One mechanism of immune evasion utilized by human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) envelope glycoproteins is the presence of a dense carbohydrate shield. Accumulating evidence from in vitro and in vivo experiments suggests that alterations in N-linked glycosylation of SIV gp120 can enhance host humoral immune responses that may be involved in immune control. The present study was designed to determine the ability of glycosylation mutant viruses to redirect antibody responses to shielded envelope epitopes. The influence of glycosylation on the maturation and specificity of antibody responses elicited by glycosylation mutant viruses containing mutations of specific N-linked sites in and near the V1 and V2 regions of SIVmac239 gp120 was determined. Results from these studies demonstrated a remarkably similar maturation of antibody responses to native, fully glycosylated envelope proteins. However, analyses of antibodies to defined envelope domains revealed that mutation of glycosylation sites in V1 resulted in increased antibody recognition to epitopes in V1. In addition, we demonstrated for the first time that mutation of glycosylation sites in V1 resulted in a redirection of antibody responses to the V3 loop. Taken together, these results demonstrate that N-linked glycosylation is a determinant of SIV envelope B-cell immunogenicity in addition to in vitro antigenicity. In addition, our results demonstrate that the absence of N-linked carbohydrates at specific sites can influence the exposure of epitopes quite distant in the linear sequence.

Loss of a Conserved N-Linked Glycosylation Site in the Simian Immunodeficiency Virus Envelope Glycoprotein V2 Region Enhances Macrophage Tropism by Increasing CD4-Independent Cell-to-Cell Transmission

“…These structures suggest that changes in the N173/N160 glycosylation site may affect V1/V2 and V3 interactions, which in turn may influence trimer structure and Env-CCR5 interactions, since V3 forms part of the CCR5 binding site. N-linked glycans in the V1/V2 region have also been identified as determinants of neutralization sensitivity, fusion activity, and CD4-independent infection (18,(57)(58)(59)(60)(61)(62)(63)(64) and may alter the position of the V1/V2 loop (64). N481 is located in the outer domain of gp120, which is on the surface of the Env trimer, in close proximity to the CD4 binding loop.…”

Engineering, Expression, Purification, and Characterization of Stable Clade A/B Recombinant Soluble Heterotrimeric gp140 Proteins

“…glycosylation sites either to occlude immunodominant but variable regions or to enhance the exposure of conserved neutralization epitopes, respectively (10,17,32,50,64,66); repositioning of conserved epitopes within more variable, but also more immunogenic, regions of the HIV Env (48, 51); design of non-HIV Env scaffold proteins that express epitopes of broadly neutralizing antibodies (11,18,19,39,62,63); molecular evolution-based approaches (24); generation of ancestral or consensus Env sequences (23,31,45,46,52); and others. Thus far, all of these approaches have had a very limited success in the elicitation of broad and potent neutralizing antibody responses against tier 2 HIV-1 viruses.…”

Identification of an N-Linked Glycosylation in the C4 Region of HIV-1 Envelope gp120 That Is Critical for Recognition of Neighboring CD4 T Cell Epitopes

“…Although many studies have shown the profound effects of Nlinked glycans on the envelope gp120 of HIV or SIV on Ab and CD8 T cell responses to these Ags (31)(32)(33)(34)(35)(36)(37)(38), very little is known about how these glycans affect gp120 Ag processing and its MHC-II presentation to the CD4 T cells. Previous studies have shown that CD4 T cell epitopes tend to cluster at specific nonglycosylated gp120 regions that are flanked with multiple N-linked glycosylation sites (39,40), but it is not known how these N-glycans actually influence CD4 T cell recognition of gp120 epitopes.…”