Role of N-linked glycans in the interaction between the envelope glycoprotein of human immunodeficiency virus and its CD4 cellular receptor. Structural enzymatic analysis.

gp120 and CD4 are two glycoproteins that are considered to interact together to allow the binding of HIV to CD4+ cells. We have utilized enzymatic digestion by endoglycosidases in order to analyze N-linked carbohydrate chains of these proteins and their possible role in the interaction of gp120 or gp160 with CD4. SDS denaturation was not necessary to obtain optimal deglycosylation of either molecule, but deglycosylation of CD4, nonetheless, depended on the presence of 1% Triton X-100. Endo H and Endo F that cleave high mannose type and biantennary glycans diminish the molecular mass of the glycoproteins from 120 or 160 Kd to 90 or 130 Kd, respectively; but these enzymes had no action on CD4 glycans. Endo F N-glycanase mixture, which acts on all glycan species, including triantennary chains, led to complete deglycosylation of gp120/160 and of CD4. Therefore, probably half of the glycan moieties of gp120/160 are composed of high mannose and biantennary chains, the other half being triantennary species. The carbohydrate structures of CD4 seems to be triantennary chains. To analyze the binding of gp120/160 to CD4, we used a molecular assay in which an mAb (110-4) coupled to Sepharose CL4B allowed the attachment of soluble gp120/160 to the beads; 125I-sCD4 was then added to measure the binding of CD4 to different amounts of gp120/160. Binding to gp160 was not modified when using completely deglycosylated 125I-sCD4, while deglycosylation of gp120 or of gp160 resulted in the decrease of the binding to native CD4 by two- and fivefold, respectively. Native and deglycosylated gp120/160 bound to CD4+ cells with comparable affinities. In addition, deglycosylated gp120 displaced 125I-gp160 binding to CD4+ cells and inhibited fusion of fresh Molt-T4 cells with CEM HIV1- or HIV2-infected cells to the same extent. Taken together, these results indicate that carbohydrates of CD4 and of gp120/160 do not play a significant role in the in vitro interaction between these two molecules.

A molecular mechanism of inhibition of HIV-1 binding to CD4+ cells by monoclonal antibodies to gp110.

We have investigated the possible involvement in the interaction between HIV gp110 and its CD4 receptor of epitopes different from the currently known binding site(s) of the molecule. Four monoclonal antibodies (MAbs) to gp110 were used (Genetic Systems Corporation, Seattle, Washington, USA): one (110-1) recognized a peptide corresponding to the C-terminal part of gp110 (494-517); the other three (110-3, 110-4, 110-5) recognized the same peptide located at position 308-328. HIV or purified gp110 obtained from a vaccinia recombinant (Transgene S.A., Strasbourg, France) were pre-incubated with the MAb prior to addition to CD4+ cells. Specific binding of viral particles or of the soluble molecule was then determined by flow cytometer analysis, compared with that of control preparations where the MAb was added after HIV or gp 110 had been allowed to bind CD4+ cells. Significant inhibition of HIV binding was noted with the three MAbs to peptide (308-328), but not with 110-1. At the molecular level, these same MAbs decreased the affinity of interaction between CD4 and soluble gp110, although they could still label the latter molecule after it had bound to CD4+ cells. Therefore, steric hindrance may account for neutralization of HIV binding by antibodies that are actually directed to epitopes topographically distinct from the site of binding of gp110 to CD4.

Use of synthetic peptides for the detection of antibodies against the nef regulating protein in sera of HIV-infected patients.

Human sera were tested for the presence of anti-nef antibodies by radioimmunoassay (RIA), with recombinant radiolabelled nef expressed in E. coli. Of the 300 HIV-positive sera tested by RIA, 70 +/- 5.3% were found to be anti-nef positive. Anti-nef antibodies bound to nef with a high affinity (K 0.5 = 2.2 x 10(-9) M). In 31 of the sera, the specificity of anti-nef antibodies was further analysed by enzyme-linked immunosorbent assay (ELISA) with large synthetic peptides ranging from 31 to 66 amino acid residues and spanning the total sequence of nef from HIV-1. The results obtained showed that the immunodominant antigenic sites of nef were located close to the N- and C-terminal regions of the molecule.

Production and characterization of human monoclonal antibodies against core protein p25 and transmembrane glycoprotein gp41 of HIV-1.

With a view to obtaining human monoclonal antibodies against HIV-1 antigens we used the Epstein-Barr virus immortalization technique to induce lymphoblastoid cell lines from peripheral blood lymphocytes of 10 people who were seropositive for HIV-1 and had no clinical symptoms. A number of polyclonal lines were obtained which synthesized antibodies against most of the major proteins and glycoproteins of HIV-1. Three stable clones were characterized for class, secretion characteristics and specificity. Two of these clones produce antibodies which react with gp41, and the third reacts with p25. One of the anti-gp41 antibodies was found to have neutralizing activity.

Accessibility of the highly conserved amino- and carboxy-terminal regions from HIV-1 external envelope glycoproteins.

Amino- and carboxy-terminal extremities of the envelope external glycoproteins are regions that have remained highly conserved between human immunodeficiency viruses HIV-1 and HIV-2. The corresponding peptides have been synthesized and their structure and function analyzed. Circular dichroism spectra showed evidence of alpha helical conformation when the peptides were dissolved in the nonpolar solvent trifuoroethanol. These two regions are indeed exposed on the molecule because they were accessible to their respective specific antibodies on the native gp160 precursor or processed gp120 glycoproteins of HIV-1. Neither the peptides nor rabbit or human antibodies directed against the N- and C-terminal peptides interfered with the interaction between HIV-1 external glycoprotein gp120 and its CD4 cellular receptor. Taken together, these results indicate that N- and C-terminal regions of gp120 are accessible on the quaternary structure of the virion as well as on the soluble form of gp120 and that these regions are not directly or indirectly involved in the binding of gp120 to CD4.

N-Acetyl-beta-D-glucosaminyl-binding properties of the envelope glycoprotein of human immunodeficiency virus type 1.

The effect of carbohydrate structures on the adsorption of HIV-1 or of recombinant envelope glycoprotein gp 160 (rgp 160) to cells of the CEM line was investigated with an indirect immunofluorescence assay using gp 120-specific mouse monoclonal antibodies (mAbs) directed to envelope gp 120. The beta-D-galactosyl, alpha-D-mannosyl, beta-D-glucosyl, N-acetyl-beta-D-glucosaminyl, sialosyl, and L-fucosyl derivatives tested had no effect on this binding. However, preincubation of HIV-1 (or rgp 160) with the neoglycoprotein, beta-D-GlcNAc47-BSA, specifically inhibited the labeling, by some of the mAb used, of HIV-1 (or rgp 160) bound at the cell membrane. This inhibition occurred only with mAbs that were specific for the immunodominant "neutralizing" third variable region (V3) of gp 120. Competition for the binding to rgp 160 between beta-D-GlcNAc47-BSA and mAb was further demonstrated by use of affinity matrices substituted with one of the relevant mAb (110-4), or with beta-D-GlcNAc47-BSA. Besides beta-D-GlcNAc47-BSA-Sepharose, rgp 160 also bound with low affinity, but high specificity, to two other N-acetyl-beta-D-glucosaminyl affinity matrices, beta-D-GlcNAc-divinylsulfone-agarose and asialoagalactothyroglobulin-agarose. Conversely, beta-D-[125I]GlcNAc47-BSA bound specifically to gp 160-Sepharose. These results indicated that rgp 160 behaves as a N-acetyl-beta-D-glucosaminyl-binding protein for GlcNAc residues presented at high density on a carrier, the carbohydrate-binding site of which is close to, or located on the V3 region of gp 120.

Specificity of anti-peptide antibodies elicited against synthetic peptides mimicking conserved regions of HIV1 envelope glycoprotein.

Comparison of HIV1Bru and HIV2Rod external envelope glycoprotein sequences enabled us to select ten highly conserved peptide sequences. The corresponding peptides were chemically synthesized, then coupled to bovine serum albumin before injection in rabbits. Although all peptides were immunogenic, only antibodies directed against peptides P1 (amino acid residues 33-55), P22 (418-462), P8 (487-508) and P21 (487-534) were able to interact with significant affinity (K0.5 about 10(-6) to 10(-8) M) with the native glycoprotein by radioimmunoassay. Noteworthy was the capacity of anti-P1 antibodies to also recognize the glycoprotein of HIV2. Anti-peptide antibodies were tested for their ability to interfere with the gp120-CD4 interaction, membrane fusion and virus replication. Preincubation of gp120 with antibodies directed to the region previously described as the putative CD4-binding site, P22 (418-462), did not abolish gp120 binding to CD4-positive cells.