Deletion of the GPG motif in the HIV type 1 V3 loop does not abrogate infection in all cells

Novel small synthetic HIV-1 V3 crown variants: CCR5 targeting ligands

The CC chemokine receptor 5 (CCR5) antagonism represents a promising pharmacological strategy for therapeutic intervention as it plays a significant role in reducing the severity and progression of a wide range of pathological conditions. Here we designed and generated peptide ligands targeting the chemokine receptor, CCR5, that were derived from the critical interaction sites of the V3 crown domain of envelope protein glycoprotein gp120 (TRKSIHIGPGRAFYTTGEI) of HIV-1 using computational biology approach and the peptide sequence corresponding to this region was taken as the template peptide, designated as TMP-1. The peptide variants were synthesized by employing Fmoc chemistry using polymer support and were labelled with rhodamine B to study their interaction with the CCR5 receptor expressed on various cells. TMP-1 and TMP-2 were selected as the high-affinity ligands from in vitro receptor-binding assays. Specific receptor-binding experiments in activated peripheral blood mononuclear cells and HOS.CCR5 cells indicated that TMP-1 and TMP-2 had significant CCR5 specificity. Further, the functional analysis of TMP peptides using chemotactic migration assay showed that both peptides did not mediate the migration of responsive cells. Thus, template TMP-1 and TMP-2 represent promising CCR5 targeting peptide candidates.

Activity of the small modified amino acid alpha-hydroxy glycineamide on in vitro and in vivo human immunodeficiency virus type 1 capsid assembly and infectivity

Upon maturation of the human immunodeficiency virus type 1 (HIV-1) virion, proteolytic cleavage of the Gag precursor protein by the viral protease is followed by morphological changes of the capsid protein p24, which will ultimately transform the virus core from an immature spherical to a mature conical structure. Virion infectivity is critically dependent on the optimal semistability of the capsid cone structure. We have reported earlier that glycineamide (G-NH(2)), when added to the culture medium of infected cells, inhibits HIV-1 replication and that HIV-1 particles with aberrant core structures were formed. Here we show that it is not G-NH(2) itself but a metabolite thereof, alpha-hydroxy-glycineamide (alpha-HGA), that is responsible for the antiviral activity. We show that alpha-HGA inhibits the replication of clinical HIV-1 isolates with acquired resistance to reverse transcriptase and protease inhibitors but has no effect on the replication of any of 10 different RNA and DNA viruses. alpha-HGA affected the ability of the HIV-1 capsid protein to assemble into tubular or core structures in vitro and in vivo, probably by binding to the hinge region between the N- and C-terminal domains of the HIV-1 capsid protein as indicated by matrix-assisted laser desorption ionization-mass spectrometry results. As an antiviral compound, alpha-HGA has an unusually simple structure, a pronounced antiviral specificity, and a novel mechanism of antiviral action. As such, it might prove to be a lead compound for a new class of anti-HIV substances.

Conformational study of palindromic tripeptides (GPG, IPI and KPK) in HIV-1 protease--a density functional theory study

A comparative study has been carried out on three palindromic tripeptides Gly-Pro-Gly, Ile-Pro-Ile and Lys-Pro-Lys which were present in HIV protein along with their analogues applying density functional computation at B3LYP/6-31G* level of theory. Discrepancy from the structural analysis has been noted for all the systems and it was found to be more for amide capped structure at the C terminal of proline. The puckering amplitude A and Phase angle P of the pyrrolidine ring of proline in the chosen palindromic tripeptides and their analogues were calculated from the endocyclic torsion angles. The minimum energy conformers lying well within the prescribed region of proline were obtained for the derived compounds from potential energy surface scan mentioning that no role has been played by its terminal residues. This is further supported by the simulated amide bands identifying the helical structure for all three palindromic tripeptides signifying the importance of proline. The molecular properties such as stabilization energy, chemical hardness along with dipole moment were calculated and interpreted. The values of Calpha-H(s) and the peptide backbone N-Calpha-CO for all the selected conformers specify the three palindromic tripeptides to have a symmetrical achiral structure.

Monocyte-derived macrophages and myeloid cell lines as targets of HIV-1 replication and persistence

HIV infection of mononuclear phagocytes (MP), mostly as tissue macrophages, is a dominant feature in the pathogenesis of HIV disease and its progression to AIDS. Although the general mechanism of infection is not dissimilar to that of CD4+ T lymphocytes occurring via interaction of the viral envelope with CD4 and a chemokine receptor (usually CCR5), other features are peculiar to MP infection. Among others, the long-term persistence of productive infection, sustained by the absence of substantial cell death, and the capacity of the virions to bud and accumulate in intracellular multivesicular bodies (MVB), has conferred to MP the role of "Trojan horses" perpetuating the chronic state of infection. Because the investigation of tissue macrophages is often very difficult for both ethical and practical reasons of accessibility, most studies of in vitro infection rely upon monocyte-derived macrophages (MDM), a methodology hampered by inter-patient variability and lack of uniformity of experimental protocols. A number of cell lines, mostly Mono Mac, THP-1, U937, HL-60, and their derivative chronically infected counterparts (such as U1 and OM-10.1 cell lines) have complemented the MDM system of infection providing useful information on the features of HIV replication in MP. This article describes and compares the most salient features of these different cellular models of MP infection by HIV.

Enforcing solution phase nanoscopic aggregation in a palindromic tripeptide

C-terminal dimerization of a tripeptide palindrome afforded fibrillation in solution through an assembly probably driven by hydrogen bonding and hydrophobic contributions; such an approach provides an expeditious entry into fabrication of fibrillating peptides from non-fibrillating peptide sequences.

Selected amino acid substitutions in the C-terminal region of human immunodeficiency virus type 1 capsid protein affect virus assembly and release

The capsid protein (CA or p24) of human immunodeficiency virus type 1 (HIV-1) plays a major role both early and late in the virus replication cycle. Many studies have suggested that the C-terminal domain of this protein is involved in dimerization and proper assembly of the viral core. Point mutations were introduced in two conserved sites of this region and their effects on viral protein expression, particle assembly and infectivity were studied. Eight different mutants (L205A+P207A, L205A, P207A, 223GPG225AAA, G223A, P224A, G225A and V221G) of the infectious clone pNL4-3 were constructed. Most substitutions had no substantial effect on HIV-1 protein synthesis, yet they impaired viral infectivity and particle production. The two mutants P207A and V221G also had a profound effect on Gag–Pol protein processing in HeLa–tat cells. However, these results were cell line-specific and Gag–Pol processing of P207A was not affected in 293T cells. In HeLa–tat cells, no virus particles were detected with the P207A mutation, whereas the other mutant virus particles were heterogeneous in size and morphology. None of the mutants showed normal, mature, conical core structures in HeLa–tat cells. These results indicate that the two conserved sequences in the C-terminal CA domain are essential for proper morphogenesis and infectivity of HIV-1 particles.

gp120 sequences from HIV type 1 subtype C early seroconverters in India

A limited number of full-length gp120 sequences are currently available for subtype C HIV-1 from India. Sequence data from HIV-1 subtype C in early seroconverter stage virus are also very limited. With the objective of identifying the sequence variation in early seroconverters, we compared Indian subtype C gp120 sequences obtained from six early seroconverters presented in this study with non-Indian subtype C sequences from other parts of the world obtained from the Los Alamos database and subtype C potential vaccine candidate sequences. All these samples were collected within a few weeks of seroconversion and hence they represent gp120 sequences of currently circulating viral strains in India. The phylogenetic tree indicated that the Indian sequences compared here clustered together within the C clade. The seroconverter sequences presented in the study would surely help in identifying the immunogenic epitopes and could be utilized further for developing effective prophylactic strategies against HIV-1 subtype C for India.

Human CD38 interferes with HIV-1 fusion through a sequence homologous to the V3 loop of the viral envelope glycoprotein gp120

CD38 is a progression marker in HIV-1 infection, it displays lateral association with CD4, and down-modulates gp120/CD4 binding. The aim of this study was to elucidate the mechanism behind the interplay between CD4, CD38, and HIV-1. We used mouse cell transfectants expressing human CD4 and either CD38 or other CD4-associated molecules to show that CD38 specifically inhibits gp120/CD4 binding. Human cell transfectants expressing truncated forms of CD38 and bioinformatic analysis were used to map the anti-HIV activity and show that it is concentrated in the membrane-proximal region. This region displayed significant sequence-similarity with the V3 loop of the HIV-1 gp120 glycoprotein. In line with this similarity, synthetic soluble peptides derived from this region reproduced the anti-HIV effects of full-length CD38 and inhibited HIV-1 and HIV-2 primary isolates from different subtypes and with different coreceptor use. A multiple-branched peptide construct presenting part of the sequence of the V3-like region potently and selectively inhibited HIV-1 replication in the nanomolar range. Conversely, a deletion in the V3-like region abrogated the anti-HIV-1 activity of CD38 and its lateral association with CD4. These findings may provide new insights into the early events of HIV-1 fusion and strategies to intervene.

Potential new therapies for the treatment of HIV-1 infection

The development and clinical use of chemotherapeutic agents for the treatment of persistent HIV-1 infection over the past decade has profoundly and favorably affected the course of HIV-1 disease for many infected individuals. Unfortunately, the long-term use of these therapies is complicated by unwanted metabolic side effects, by issues of adherence, and by the selection of viral variants with reduced susceptibility. These complications have spurred the search for new anti-HIV-1 agents having improved pharmacological properties and expressing activity against viral variants resistant to the currently available agents. This brief review describes the current state of this search as well as potentially novel viral targets for chemotherapeutic intervention.

Expression of CD4 controls the susceptibility of THP-1 cells to infection by R5 and X4 HIV type 1 isolates

The monocytic THP-1 cell line has been used to study HIV-monocyte/macrophage interactions and the relationship between differentiation, virus production, and virus latency. Undifferentiated THP-1 cells are susceptible to infection by T-tropic human immunodeficiency virus type 1 (HIV-1) isolates that use the coreceptor CXCR4 (X4 strains). Treatment with phorbol 12-myristate 13-acetate (PMA) induces differentiation of THP-1 cells into adherent macrophage-like cells, which are susceptible to M-tropic, CCR5-dependent isolates (R5 strains). The aim of this study was to determine whether variabilities observed in the susceptibility of THP-1 cells to HIV-1 infection may be related to the differential expression of CD4, CCR5, and CXCR4. Both propagation and PMA treatment of THP-1 cells resulted in a marked decrease in CD4-positive cells, whereas the expression of CCR5 and CXCR4 was not reduced during propagation. Both coreceptors were also relatively "resistant" to PMA-induced downregulation when compared with the low percentage of CD4-positive cells in differentiated cultures. In undifferentiated THP-1 cells, low CD4 expression significantly reduced the susceptibility of the cells to infection with the R5 HIV-1(BaL) isolate, whereas a PMA-induced decrease in CD4 expression reduced permissiveness of the cells to the X4 HIV-1(IIIB) isolate. Thus, cell surface CD4 plays a primary role in determining how efficiently THP-1 cells can be infected with the X4 and the R5 isolates.