Steps Of HIV-1 Infection Research Articles

Structure−Activity Relationships in the Binding of Chemically Derivatized CD4 to gp120 from Human Immunodeficiency Virus

The first step in HIV infection is the binding of the envelope glycoprotein gp120 to the host cell receptor CD4. An interfacial "Phe43 cavity" in gp120, adjacent to residue Phe43 of gp120-bound CD4, has been suggested as a potential target for therapeutic intervention. We designed a CD4 mutant (D1D2F43C) for site-specific coupling of compounds for screening against the cavity. Altogether, 81 cysteine-reactive compounds were designed, synthesized, and tested. Eight derivatives exceeded the affinity of native D1D2 for gp120. Structure-activity relationships (SAR) for derivatized CD4 binding to gp120 revealed significant plasticity of the Phe43 cavity and a narrow entrance. The primary contacts for compound recognition inside the cavity were found to be van der Waals interactions, whereas hydrophilic interactions were detected in the entrance. This first SAR on ligand binding to an interior cavity of gp120 may provide a starting point for structure-based assembly of small molecules targeting gp120-CD4 interaction.

The temperature arrested intermediate of virus-cell fusion is a functional step in HIV infection

HIV entry occurs via membrane-mediated fusion of virus and target cells. Interactions between gp120 and cellular co-receptors lead to both the formation of fusion pores and release of the HIV genome into target cells. Studies using cell-cell fusion assays have demonstrated that a temperature-arrested state (TAS) can generate a stable intermediate in fusion related events. Other studies with MLV pseudotyped with HIV envelope also found that a temperature sensitive intermediate could be generated as revealed by the loss of a fluorescently labeled membrane. However, such an intermediate has never been analyzed in the context of virus infection. Therefore, we used virus-cell infection with replication competent HIV to gain insights into virus-cell fusion. We find that the TAS is an intermediate in the process culminating in the HIV infection of a target cell. In the virion-cell TAS, CD4 has been engaged, the heptad repeats of gp41 are exposed and the complex is kinetically predisposed to interact with coreceptor to complete the fusion event leading to infection.

Designing decoys for chemokine-chemokine receptor interaction.

Aberrant expression of chemokines and their receptors play causative roles in the pathophysiology of numerous autoimmune and inflammatory disease processes. Moreover, an integral step in HIV infection involves binding to chemokine receptors, and hence chemokines are intimately linked to HIV-related diseases. Therefore, chemokines and their receptors are excellent targets for developing drugs that are more specific and may be of benefit in the management of disease. Knowledge of the chemokine and chemokine receptor structures, and an understanding of the structural basis of their function are essential for structure-aided design of receptor decoys. Chemokine ligands bind their receptors with nanomolar (nM) affinity, and successful design of a small molecule antagonist should bind the receptor with similar high affinity and specificity. Chemokines bind receptors that belong to the 7-transmembrane class on leukocytes, and highly negatively charged proteoglycans that are present on the cell surface. Structure-function studies have identified regions in both the ligand and the receptor that mediate binding and activation. Structures of numerous chemokines have been solved though very little is known regarding receptor structures. This review will summarize the current knowledge on the structures, structure-function, and the efficacy of chemokine derivatives and functional domain peptides as antagonists, and discuss strategies for exploiting this information for designing decoys for inflammatory, autoimmune, and HIV-related diseases.

Trans-activated interferon-alpha2 delivered to T cells by SV40 inhibits early stages in the HIV-1 replicative cycle.

Several lines of evidence suggest a potential major role for interferon (IFN) in controlling HIV-1 replication. However, this inhibition is moderate and is reversible upon IFN removal. To achieve prolonged high concentrations of IFN at the site of infection, we devised an SV40-based vector, SV[HIVLTR]IFN, to direct the synthesis of human IFN-alpha2, by employing a virus-trans-activated human IFN-alpha2 gene to be transcribed in response to HIV-1 infection. Expression of IFN-alpha2 was confirmed by Northern and Western blotting, in SV[HIVLTR]IFN-transduced, HIV-1-challenged human lymphocyte lines and primary human lymphocytes. SV[HIVLTR]IFN-transduced cells showed no evidence of HIV-1-related cytophatic effects when challenged with high doses of HIV-1(NL4-3). As measured by supernatant HIV-1 p24 antigen concentration, IFN-alpha2-expressing cell lines and peripheral blood lymphocytes (PBL) were protected from high-dose challenges of HIV-1. rSV40-delivered IFN-alpha2 inhibited gp120 protein synthesis and expression of HIV-1 mRNAs. Finally, Southern analysis revealed that levels of proviral DNA were markedly reduced in SV[HIVLTR]IFN-transduced cells compared to control cultures. IFN-alpha2 expression driven by HIVLTR delivered by an rSV40 vector thus strongly inhibits HIV-1 replication, probably by blocking a preintegration step in HIV-1 infection. Targeted expression of IFN-alpha2 delivered by SV40 can thus repress HIV-1 replication, and may be a useful approach to HIV-1 treatment.

Properties of quadruplex oligonucleotides with anti-HIV-1 activity.

A phosphorothioate oligonucleotide composed of deoxyguanosine and thymidine was identified as an inhibitor of HIV-1 infection at an early stage of the HIV-1 replication cycle in vitro. The phosphodiester and phosphorothioate chimeric oligonucleotides were found to be potent inhibitors of several steps of HIV-1 infection: the interaction with CD4 and the chemokine receptor, the reverse transcriptase activity, and the integrase activity. To elucidate the mechanism of the anti-HIV-1 function of these oligonucleotides in terms of their structure, we focussed on their G-serial sequences and investigated the characteristics of their solution structures. These oligonucleotides were proved to be able to adopt G-quadruplex structures by UV and CD measurements. We presume that the anti-HIV-1 activities of these oligonucleotides are consequently attributable to G-quadruplex formation.

Human Milk Glycoconjugates That Inhibit Pathogens

Breast-fed infants have lower incidence of diarrhea, respiratory disease, and otitis media. The protection by human milk has long been attributed to the presence of secretory IgA. However, human milk contains large numbers and amounts of complex carbohydrates, including glycoproteins, glycolipids, glycosaminoglycans, mucins, and especially oligosaccharides. The oligosaccharides comprise the third most abundant solid constituent of human milk, and contain a myriad of structures. Complex carbohydrate moieties of glycoconjugates and oligosaccharides are synthesized by the many glycosyltransferases in the mammary gland; those with homology to cell surface glycoconjugate pathogen receptors may inhibit pathogen binding, thereby protecting the nursing infant. Several examples are reviewed: A fucosyloligosaccharide inhibits the diarrheagenic effect of stable toxin of Escherichia coli. A different fucosyloligosaccharide inhibits infection by Campylobacter jejuni. Binding of Streptococcus pneumoniae and of enteropathogenic E. coli to their respective receptors is inhibited by human milk oligosaccharides. The 46-kD glycoprotein, lactadherin, inhibits rotavirus binding and infectivity. Low levels of lactadherin in human milk are associated with a higher incidence of symptomatic rotavirus in breast-fed infants. A mannosylated glycopeptide inhibits binding by enterohemorrhagic E. coli. A glycosaminoglycan inhibits binding of gp120 to CD4, the first step in HIV infection. Human milk mucin inhibits binding by S-fimbriated E. coli. The ganglioside, GM1, reduces diarrhea production by cholera toxin and labile toxin of E. coli. The neutral glycosphingolipid, Gb3, binds to Shigatoxin. Thus, many complex carbohydrates of human milk may be novel antipathogenic agents, and the milk glycoconjugates and oligosaccharides may be a major source of protection for breastfeeding infants.

Study reveals key step in HIV-1 infection of the brain

Study reveals key step in HIV-1 infection of the brain

A domain of human immunodeficiency virus type 1 Vpr containing repeated H(S/F)RIG amino acid motifs causes cell growth arrest and structural defects.

Vpr is a virion-associated protein of human immunodeficiency type 1 (HIV-1) whose function in acquired immunodeficiency syndrome (AIDS) has been uncertain. Employing the yeast Saccharomyces cerevisiae as a model to examine the effects of HIV-1 auxiliary proteins on basic cellular functions, we found that the vpr gene caused cell growth arrest and structural defects indicated by osmotic sensitivity and gross cell enlargement. Production of various domains by gene expression showed that this effect arose from within the carboxyl-terminal third of the Vpr protein and implicated the sequence HFRIGCRHSRIG, containing two H(S/F)RIG motifs. Electroporation with a series of peptides containing these motifs caused structural defects in yeast that resulted in osmotic sensitivity. A protein with functions relating to the yeast cytoskeleton, Sac1p [Cleves, A. E., Novick, P.J. & Bankaitis, V.A. (1989) J. Cell Biol. 109, 2939-2950], shows sequence similarity to Vpr, and Vpr's effect in yeast may be to disrupt normal Sac1p functions. The Sac1p equivalent has not yet been described in mammalian cells, but in rhabdomyosarcoma and osteosarcoma cell lines Vpr also caused gross cell enlargement and replication arrest [Levy, D.N., Fernandes, L.S., Williams, W.V. & Weiner, D.B. (1993) Cell 72, 541-550]. We note that there is a correlation between the region containing the H(S/F)RIG motifs and the pathogenicity of primate lentiviruses and we suggest that the function of Vpr may be to bring about cell growth arrest and/or cytoskeletal changes as an early step in HIV-1 infection.

Inhibition of HIV infection by a novel CD4 domain 2-specific monoclonal antibody. Dissecting the basis for its inhibitory effect on HIV-induced cell fusion.

HIV use the CD4 molecule as their primary cellular receptor. Residues in the N-terminal domain (D1) of CD4 are crucial to HIV attachment through the gp120 envelope component. However, other regions of CD4 appear to be required subsequently for virus- and cell-cell fusion. Little is understood of the post-binding steps which may differ between HIV variants. We report a novel anti-CD4 mAb that does not block CD4/gp120 binding, but that does efficiently block both viral infection and cell-cell syncytia formation, and define its contact site as residues in CD4 D2 using both mouse/human CD4 chimeras and CD4 substitution mutants. We also investigated the basis for its antiviral effect. Using the CD4 D2 specific mAb, we identify another conserved step in HIV infection, as evidenced by its ability to neutralize a broad range of primary isolates and T cell-line passaged strains. Monovalent forms of the mAb were used to determine if its activity was due to masking of the D2 epitope, to steric inhibition, or bivalency. Our data indicate that both binding site and bivalency of the mAb underlie its potency. The need for bivalency is not simply explained by affinity, because monovalent forms can displace the intact mAb and reverse its protective effect. These results provide evidence that binding of the D2-specific mAb prevents structural alterations necessary for membrane fusion.

Pradimicin A inhibition of human immunodeficiency virus: Attenuation by mannan

The mechanism of action of a novel anti-HIV antibiotic, pradimicin A, has been studied using cell-free (MT-4 cells) and cell to cell (MOLT-4 and MOLT-4/HIV HTLV-3B Cells) HIV infection systems. The data indicate that (1) preincubation of the cells with HIV at 0° for 1 hr, followed by the addition of pradimicin A and further incubation at 37°, resulted in a complete inhibition of infection while preincubation at 37° did not. Similar data were obtained with the coculture between MOLT-4 and MOLT-4/HIV cells. (2) Virus treated with pradimicin A followed by washing did not show any inhibition on subsequent HIV binding to cells. (3) The inhibitory effect of pradimicin A on HIV infection was prevented by mannan but not by other sugars tested. Mannan, however, did not interfere with the anti-HIV activity of other known inhibitors. (4) Use of EGTA suggested that pradimicin A required Ca ions to exert its anti-HIV activity. These data imply that pradimicin A inhibits an early step in HIV infection, probably through its binding to mannose residues of HIV glycoprotein.