The N-terminal V3 loop glycan modulates the interaction of clade A and B human immunodeficiency virus type 1 envelopes with CD4 and chemokine receptors - PubMed (original) (raw)

The N-terminal V3 loop glycan modulates the interaction of clade A and B human immunodeficiency virus type 1 envelopes with CD4 and chemokine receptors

S E Malenbaum et al. J Virol. 2000 Dec.

Abstract

We investigated the underlying mechanism by which the highly conserved N-terminal V3 loop glycan of gp120 conferred resistance to neutralization of human immunodeficiency virus type 1 (HIV-1). We find that the presence or absence of this V3 glycan on clade A and B viruses accorded various degrees of susceptibility to neutralization by antibodies to the CD4 binding site, CD4-induced epitopes, and chemokine receptors. Our data suggest that this carbohydrate moiety on gp120 blocks access to the binding site for CD4 and modulates the chemokine receptor binding site of phenotypically diverse clade A and clade B isolates. Its presence also contributes to the masking of CD4-induced epitopes on clade B envelopes. These findings reveal a common mechanism by which diverse HIV-1 isolates escape immune recognition. Furthermore, the observation that conserved functional epitopes of HIV-1 are more exposed on V3 glycan-deficient envelope glycoproteins provides a basis for exploring the use of these envelopes as vaccine components.

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Figures

FIG. 1

FIG. 1

(A) Partial V3 loop sequence, coreceptor use, classification, and state of V3 glycosylation of the viruses used. X4, CXCR4 using; R5, CCR5 using; + and −, presence and absence, respectively, of the N-linked glycan at amino acid 301 of envelope gp120 (numbered according to the prototype HXBc2 sequence [21]). (B) Immunoblot analyses of envelope-transfected cell lysates. The position of migration of the gp120 glycoprotein is shown.

FIG. 2

FIG. 2

Neutralization of viruses with the HIV-1SF33 WT and V3T envelope glycoproteins. Recombinant viruses encoding the luciferase gene and bearing either the WT (open symbols) or V3T (solid symbols) envelopes of HIV-1SF33 were incubated with different concentrations of (A) IgGCD4 and CD4BS antibodies IgG1b12 and F105 and (B) CD4i site antibodies 17b, 48d, and A1g8. The virus-antibody mixtures were then inoculated onto HOS T4 X4 cells. Luciferase activity in infected cell lysates was assessed 3 days later and is expressed as the percent inhibition of activity seen in the absence of antibodies. The results shown are representative of three independent experiments.

FIG. 3

FIG. 3

Neutralization of viruses with the HIV-1SF162 WT and V3A envelope glycoproteins. The ability of (A) IgGCD4 and CD4BS antibodies IgG1b12 and F105 and (B) CD4i antibodies 17b, 48d, and A1g8 to neutralize infection of HOS T4 R5 cells with luciferase reporter viruses carrying the HIV-1SF162 WT (solid symbols) and V3A (open symbols) envelopes were determined as described in the legend to Fig. 2. The results shown are representative of those obtained in three independent experiments.

FIG. 4

FIG. 4

Neutralization of HIV-1SF170 WT and V3A reporter viruses by IgGCD4 and CD4BS antibodies IgG1b12 and F105. Neutralization with the CD4BS MAbs was performed as described above using HOS T4 R5 cells. Results are representative of three independent experiments.

FIG. 5

FIG. 5

Entry into target cells of (A) HIV-1SF33, (B) HIV-1SF162, and (C) HIV-1SF170 pseudotyped viruses with and without V3 loop glycan. The ability of recombinant viruses carrying the various envelope glycoproteins to enter target cells (HOS T4 X4 cells for HIV-1SF33 and HOS T4 R5 cells for HIV-1SF162 and HIV-1SF170) was determined by assessing the luciferase activity of infected cell lysates. Open bars represent luciferase activity associated with viruses lacking the V3 loop glycosylation site, and solid bars represent viruses that have the glycosylation site. Results from a representative of at least five independent experiments are shown.

FIG. 6

FIG. 6

Blocking of virus entry with the anti-CD4 antibody Leu3A. The ability of viruses carrying the various envelope glycoproteins to enter target cells that had been preincubated with increasing concentrations of the anti-CD4 antibody Leu3A was determined as described in Materials and Methods. Results are expressed as the percentage of luciferase activity seen in the absence of the MAb and are representative of at least three independent experiments.

FIG. 7

FIG. 7

Blocking of virus entry with anticoreceptor molecules. The ability of (A) anti-CXCR4 MAb 12G5 and (B) the bicyclam AMD3100 (36) to block entry of HIV-1SF33 WT (open symbols) and V3T (solid symbols) viruses or (C and D) anti-CCR5 MAb 2D7 to block HIV-1SF162 (C) and HIV-1SF170 (D) WT (solid symbols) and V3 loop glycosylation variants (open symbols) was determined as described in the text. Virus entry is expressed as the percentage of luciferase activity seen in the absence of MAbs or compound. The results shown are representative of three independent experiments.

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