Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019693 (HIV)
 170,526 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The causative agent of a recent outbreak of an atypical pneumonia, known as severe acute respiratory syndrome (SARS), has been identified as a coronavirus (CoV) not belonging to any of the previously identified groups. Fusion of coronaviruses with the host cell is mediated by the envelope spike protein. Two regions within the spike protein of SARS-CoV have been identified, showing a high degree of sequence conservation with the other CoV, which are characterized by the presence of heptad repeats (HR1 and HR2). By using synthetic and recombinant peptides corresponding to the HR1 and HR2 regions, we were able to characterize the fusion-active complex formed by this novel CoV by CD, native PAGE, proteolysis protection analysis, and size-exclusion chromatography. HR1 and HR2 of SARS-CoV associate into an antiparallel six-helix bundle, with structural features typical of the other known class I fusion proteins. We have also mapped the specific boundaries of the region, within the longer HR1 domain, making contact with the shorter HR2 domain. Notably, the inner HR1 coiled coil is a stable alpha-helical domain even in the absence of interaction with the HR2 region. Inhibitors binding to HR regions of fusion proteins have been shown to be efficacious against many viruses, notably HIV. Our results may help in the design of anti-SARS therapeutics.
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PMID:Structural characterization of the fusion-active complex of severe acute respiratory syndrome (SARS) coronavirus. 1516 75

Heptad repeat regions (HR1 and HR2) are highly conserved sequences located in the glycoproteins of enveloped viruses. They form a six-helix bundle structure and are important in the process of virus fusion. Peptides derived from the HR regions of some viruses have been shown to inhibit the entry of these viruses. SARS-CoV was also predicted to have HR1 and HR2 regions in the S2 protein. Based on this prediction, we designed 25 peptides and screened them using a HIV-luc/SARS pseudotyped virus assay. Two peptides, HR1-1 and HR2-18, were identified as potential inhibitors, with EC(50) values of 0.14 and 1.19microM, respectively. The inhibitory effects of these peptides were validated by the wild-type SARS-CoV assay. HR1-1 and HR2-18 can serve as functional probes for dissecting the fusion mechanism of SARS-CoV and also provide the potential of further identifying potent inhibitors for SARS-CoV entry.
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PMID:Suppression of SARS-CoV entry by peptides corresponding to heptad regions on spike glycoprotein. 1518 46

T-20 is the first in a new class of antiretroviral drugs targeting the entry stage of the virus life cycle. It is a 36 amino acid peptide that binds to the HR1 region of gp41 preventing gp41-mediated fusion with the host cell membrane. T-20 was designed based on the HR2 sequence of HIV-1 subtype B gp41, a region that shows significant genetic variation with HIV-1 subtype C sequences. In order to assess the efficacy of T-20 to inhibit subtype C isolates, a total of 23 isolates were tested for their ability to replicate in the presence of T-20. This included 15 isolates that used CCR5, five that used both CCR5 and CXCR4, and three that used CXCR4. Five of these were from patients failing other antiretroviral therapies. Sequence analysis of the HR2 region indicated that there were 10-16 amino acid changes in the region corresponding to T-20. However, all isolates were effectively inhibited by T-20 at 1 microg/ml. There were no significant differences between viruses that used CCR5 or CXCR4 to enter cells. All isolates, except one, had GIV at positions 36-38 in the HR1 region. One isolate had a GVV motif but this did not affect its sensitivity to T-20. Therefore, T-20 inhibited subtype C viruses despite significant genetic differences in the HR2 region and there was no evidence for baseline resistance to T-20. These data suggest that T-20 would be highly effective in patients with HIV-1 subtype C infection, including those failing existing antiretroviral drug regimens.
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PMID:Sensitivity of HIV type 1 subtype C isolates to the entry inhibitor T-20. 1518 21

Enfuvirtide is the first representative of a new group of antiretrovirals - fusion inhibitors, which was approved for clinical use. Due to its attachment to the HR1 domain of HIV glycoprotein gp 41 enfuvirtide blocks the fusion between the virus and the target cell. Enfuvirtide is chemically a synthetic peptide consisting of 36 amino acids which is not stable in GIT and must be administered only subcutaneously. Enfuvirtide has been registered for the use as salvage therapy of patients with multiresistance, for who it is not possible to constitute an effective combination of other available antiretrovirals.
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PMID:[Enfuvirtide]. 1522 1

Four heavily antiretroviral-experienced HIV-infected patients had significant plasma HIV-RNA reductions (>1 log) after beginning an Enfuvirtide (ENF)-based rescue regimen. However, all had viral rebound shortly thereafter, sustaining high levels of plasma viremia over 80 weeks. These patients developed rapidly genotypic and phenotypic resistance to ENF. Mutations within the HR1 env region were selected (N43D in three and G36V/D in one), resulting in high-level phenotypic resistance to ENF. Interestingly, two patients had a sustained CD4+ T-cell increase and two maintained stable CD4+ T-cell counts despite virologic failure under ENF. The possible mechanisms involved in this response were examined. Changes in virus tropism from R5 to R5/X4 were observed in two patients, in parallel with increases in ENF phenotypic resistance. Low levels of T-cell activation, T-cell turnover, and cytotoxic T lymphocyte (CTL) activity were found in all four patients. An overall increase in the proportion of viruses released from cells of the macrophage lineage was observed. In summary, single mutations at the HR1 env region result in significant loss of susceptibility to ENF. Despite virologic failure, these patients may maintain elevated CD4+ counts through a reduction in their overall immune activation.
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PMID:Evolution of genotypic and phenotypic resistance to Enfuvirtide in HIV-infected patients experiencing prolonged virologic failure. 1525 64

The end of the twentieth century saw dramatic improvements in the prognosis of HIV infection brought about by the introduction of new agents (the protease inhibitors and the non-nucleoside reverse transcriptase inhibitors) and their use in highly active combinations. However, the durability of these combination treatments is limited by a number of factors including adverse effects and extensive intra-class cross-resistance so that new antiretrovirals acting on alternative targets and having improved systemic tolerability profiles are required. The HIV binding and entry process offers several potential targets for antiviral interaction. These include gp120 binding to CD4 and to chemokine co-receptor molecules as well as the fusion process itself, which involves interactions between two leucine zipper-like 4-3 repeat regions within gp41 known as heptad repeat (HR)1 and HR2. Peptides such as enfuvirtide (formerly DP178 or T-20), that mimic the HR2 region of gp41, inhibit HIV-1 by a mechanism that is thought to involve competitive binding to HR1. This review summarises the clinical development of enfuvirtide, providing an overview of the pharmacokinetic, efficacy and safety data in various patient populations, and also considers the evidence for the key role of genotypic changes in the HR1 region (amino acids 36-45) in determining viral susceptibility to inhibition by enfuvirtide.
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PMID:HIV fusion and its inhibition in antiretroviral therapy. 1533 39

The fusion inhibitor T20 belongs to a new class of anti-human immunodeficiency virus type 1 (HIV-1) drugs designed to block entry of the virus into the host cell. However, the success of T20 has met with the inevitable emergence of drug-resistant HIV-1 variants. We describe an evolutionary pathway taken by HIV-1 to escape from the selective pressure of T20 in a treated patient. Besides the appearance of T20-resistant variants, we report for the first time the emergence of drug-dependent viruses with mutations in both the HR1 and HR2 domains of envelope glycoprotein 41. We propose a mechanistic model for the dependence of HIV-1 entry on the T20 peptide. The T20-dependent mutant is more prone to undergo the conformational switch that results in the formation of the fusogenic six-helix bundle structure in gp41. A premature switch will generate nonfunctional envelope glycoproteins (dead spikes) on the surface of the virion, and T20 prevents this abortive event by acting as a safety pin that preserves an earlier prefusion conformation.
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PMID:Emergence of a drug-dependent human immunodeficiency virus type 1 variant during therapy with the T20 fusion inhibitor. 1550 29

Entry of lentiviruses, such as human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), requires folding of two heptad repeat regions (HR1 and HR2) of gp41 into a trimer-of-hairpins, which subsequently brings virus and cell membrane into fusion. This motif is a generalized feature of viral fusion proteins and has been exploited in generating antiviral fusion agents. In the present paper, we report structural characters of Env protein from another lentivirus, bovine immunodeficiency virus (BIV), which contributes to a good animal model of HIV. BIV HR1 and HR2 regions are predicted by two different programs and expressed separately or conjointly in Escherichia coli. Biochemical and biophysical analyses show that the predicted HRs of BIV Env can form a stable trimer-of-hairpins or six-helix bundle just like that formed by feline immunodeficiency virus Env. Cell fusion assay demonstrates that the HR2 peptide of BIV can efficiently inhibit the virus-mediated cell fusion.
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PMID:Characterization of BIV Env core: implication for mechanism of BIV-mediated cell fusion. 1573 28

Enfuvirtide is a 36 amino-acid synthetic peptide derived from the HR2 sequence of the HIV-1 gp41. Enfuvirtide is different from other antiretroviral drugs by its extra-cellular action where it binds to the HR1 domain at the viral surface of the gp41. The drug inhibits the conformational change of the glycoprotein, preventing the intimate fusion between the HIV envelope and the CD4 cell membrane and finally the penetration of the viral capside into the target cells. Following a 90 mg subcutaneous injection, the plasma concentration rises rapidly to reach a 4.59 +/- 1.5 microg/ml Cmax between 5 and 7 hours. Residual concentrations are between 2.6 and 3.4 microg/ml and the bioavailability of the drug is approximately 80%. Plasma concentrations and area under curve are dose-dependant. The site of injection does not influence the pharmacokinetic parameters of the drug. Infuvirtide is not an inhibitor of the P450 cytochrome and no pharmacokinetic interactions have been reported with P450 metabolised drugs.
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PMID:[Enfuvirtide, first fusion inhibitor in the treatment of human immunodeficiency virus infection: mechanism of action and pharmacokinetics]. 1574 49

Entry of SARS-CoV into a target cell is initiated by binding of the S1 domain of spike protein to a receptor, followed by conformational changes of the spike protein S2 domain, resulting in the formation of a six-helix bundle by the heptad-repeat (HR1 and HR2) regions. Our previous studies have demonstrated that peptides derived from HR2 region could inhibit SARS-CoV entry. However, synthesis of these peptides is at high cost. In this study, we designed two recombinant proteins, one containing two HR1 and one HR2 peptides (denoted HR121), and the other consisting of two HR2 and one HR1 peptides (designated HR212). These two proteins could be easily purified with the low cost of production, exhibiting high stability and potent inhibitory activity on entry of the HIV/SARS pseudoviruses with IC(50) values of 4.13 and 0.95muM, respectively. These features suggest that HR121 and HR212 can serve as potent inhibitors of SARS-CoV entry.
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PMID:Design of recombinant protein-based SARS-CoV entry inhibitors targeting the heptad-repeat regions of the spike protein S2 domain. 1578 Dec 29


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