Structure-based, targeted deglycosylation of HIV-1 gp120 and effects on neutralization sensitivity and antibody recognition

Abstract

The human immunodeficiency virus (HIV-1) exterior envelope glycoprotein, gp120, mediates receptor binding and is the major target for neutralizing antibodies. Primary HIV-1 isolates are characteristically more resistant to broadly neutralizing antibodies, although the structural basis for this resistance remains obscure. Most broadly neutralizing antibodies are directed against functionally conserved gp120 regions involved in binding to either the primary virus receptor, CD4, or the viral coreceptor molecules that normally function as chemokine receptors. These antibodies are known as CD4 binding site (CD4BS) and CD4-induced (CD4i) antibodies, respectively. Inspection of the gp120 crystal structure reveals that although the receptor-binding regions lack glycosylation, sugar moieties lie proximal to both receptor-binding sites on gp120 and thus in proximity to both the CD4BS and the CD4i epitopes. In this study, guided by the X-ray crystal structure of gp120, we deleted four N-linked glycosylation sites that flank the receptor-binding regions. We examined the effects of selected changes on the sensitivity of two prototypic HIV-1 primary isolates to neutralization by antibodies. Surprisingly, removal of a single N-linked glycosylation site at the base of the gp120 third variable region (V3 loop) increased the sensitivity of the primary viruses to neutralization by CD4BS antibodies. Envelope glycoprotein oligomers on the cell surface derived from the V3 glycan-deficient virus were better recognized by a CD4BS antibody and a V3 loop antibody than were the wild-type glycoproteins. Absence of all four glycosylation sites rendered a primary isolate sensitive to CD4i antibody-mediated neutralization. Thus, carbohydrates that flank receptor-binding regions on gp120 protect primary HIV-1 isolates from antibody-mediated neutralization.

The Neutralization Properties of a HIV-Specific Antibody Are Markedly Altered by Glycosylation Events Outside the Antigen-Binding Domain

“…Indeed, from the point of view of the Ag/Ab interaction, it has been shown that sugar moieties that apparently lie apart from the antibody's binding site can severely influence the access of the Ab to neutralizing epitopes (57). Thus, by analogy glycans present on the Fc region of F240 can dramatically affect the virus/Ab interaction.…”

Comparison of HPLC/ESI-FTICR MS versus MALDI-TOF/TOF MS for glycopeptide analysis of a highly glycosylated HIV envelope glycoprotein

“…Additionally, glycans have been shown to play a vital role in various parasitic, bacterial, and viral disease infections [6]. For instance, interaction and fusion of the human immunodeficiency virus (HIV) with its target host cells is mediated by its envelope protein, gp160, which has over 50% of its mass comprising of glycans [7][8][9][10]. The high population and diverse range of glycans on this protein acts as a shield for the virus against the immune system; the glycans also mask epitopes that impact HIV disease progression [8,[11][12][13][14][15][16][17].…”

“…For instance, interaction and fusion of the human immunodeficiency virus (HIV) with its target host cells is mediated by its envelope protein, gp160, which has over 50% of its mass comprising of glycans [7][8][9][10]. The high population and diverse range of glycans on this protein acts as a shield for the virus against the immune system; the glycans also mask epitopes that impact HIV disease progression [8,[11][12][13][14][15][16][17]. Consequently, conducting glycoproteomics studies on this target, defining the structures and locations of glycans in the HIV envelope protein, is important in understanding how variation in glycosylation affects the functions of this protein, and the studies may also provide valuable information that can be useful in identifying new vaccine candidates.…”

Increased HIV-1 sensitivity to neutralizing antibodies by mutations in the Env V3-coding region for resistance to CXCR4 antagonists

“…5, Table S2). Some studies reported that the loss of glycosylation in V3 affects the neutralization sensitivity of some HIV-1 strains (Koch et al, 2003;Li et al, 2008;Polzer et al, 2009;Wang et al, 2013). Recently, Zolla-Pazner et al (2015) proposed that the glycan on N301 restricts the mobility of the V3 loop.…”