UMLS:C0019693 - FACTA Search

Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Target Concepts:

Query: UMLS:C0019693 (HIV)
170,526 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The metabolism of different phosphoramidate prodrugs of d4T-MP, in which the phosphate group is linked to a phenyl group and the alkyl ester of an amino acid was studied in crude CEM cell extracts. Significant (80-100%) conversion to the amino acyl d4T-MP metabolite was obtained with derivatives containing L-alanine or methyl-L-aspartic acid. A lower degree of conversion was seen with derivatives containing L-phenylalanine, L-methionine, methyl-L-glutamic acid or L-leucine. Derivatives containing D-alanine, beta-alanine, glycine, L-valine or L-lactate showed no conversion to the amino acyl d4T-MP metabolite. Overall, there was a close correlation between the anti-HIV activity of these prodrugs and their conversion rate to the amino acyl d4T-MP metabolite. Our data suggest that the enzymes involved in the formation of the amino acyl d4T-MP metabolite have a rather stringent specificity for L-alanine as the amino acid moiety. In addition, these enzymes were found to be markedly species-dependent, their activities being highest in mouse serum, followed by guinea pig serum, but only minimal in human serum. Mouse serum therefore appears to be the medium of choice to isolate and identify the enzymes that are involved in the metabolism of these phosphoramidate prodrugs.
...
PMID:Metabolism and anti-HIV activity of phosphoramidate derivatives of D4T-MP with variations in the amino acid moiety. 959 64

Leukocyte chemoattractants act through a rapidly growing subfamily of G protein-coupled receptors. We report the cloning of a novel human gene encoding an orphan receptor (ChemR23) related to the C3a, C5a and formyl Met-Leu-Phe receptors, and more distantly to the subfamilies of chemokine receptors. ChemR23 transcripts were found to be abundant in monocyte-derived dendritic cells and macrophages, treated or not with LPS. Low expression could also be detected by reverse transcription-PCR in CD4+ T lymphocytes. The gene encoding ChemR23 was assigned by radiation hybrid mapping to the q21.2-21.3 region of human chromosome 12, outside the gene clusters identified so far for chemoattractant receptors. Given the increasing number of chemoattractant receptors used by HIV-1, HIV-2 and SIV as coreceptors, ChemR23 was tested in fusion assays for potential coreceptor activity by a range of viral strains. None of the tested HIV-2 strains made use of ChemR23 as a coreceptor, but several SIV strains (SIVmac316, SIVmac239, SIVmacl7E-Fr and SIVsm62A), as well as a primary HIV-1 strain (92UG024-2) used it efficiently. ChemR23 therefore appears as a coreceptor for immunodeficiency viruses that does not belong to the chemokine receptor family. It is also a putative chemoattractant receptor relatively specific for antigen-presenting cells, and it could play an important role in the recruitment or trafficking of these cell populations. Future work will be required to identify the ligand(s) of this new G protein-coupled receptor and to define its precise role in the physiology of dendritic cells and macrophages.
...
PMID:ChemR23, a putative chemoattractant receptor, is expressed in monocyte-derived dendritic cells and macrophages and is a coreceptor for SIV and some primary HIV-1 strains. 960 76

The external envelope glycoprotein (gp125) of human immunodeficiency virus type 2 (HIV-2) contains 22 cysteine residues. The positions of the 11 disulfide bridges in HIV-2 gp125 were determined by analogy with the experimental position of the disulfide bonds found in the gp120 of HIV-1. Peptides expected to mimic all 11 disulfide-bonded domains containing from 13 to 47 amino acids were synthesized by the solid-phase method according to 9-fluorenylmethoxycarbonyl strategy, except for peptide 5, which was assembled according to t-butoxycarbonyl (Boc) strategy. Analysis of all the crude peptides showed that the expected peptides were obtained with good yields, between 75% and 85%. Peptides were purified further by high-performance liquid chromatography (HPLC) on an Aquapore RPC30 C8 column. Peptide homogeneity was more than 90%. For each peptide, linear peptides (L) were SH-iodoacetamidated, whereas cyclization of peptides (C) was performed by air oxidation. Oxidation kinetics was followed with the Ellman test and HPLC. Cyclic peptides were purified by HPLC and characterized by fast atom bombardment mass spectrometry. This analysis showed that a small quantity (<10%) of dimeric peptides (2 and 8) and cyclic peptides containing oxidized methionine or tryptophan residues (4, 9 and 10) were formed. To assess the relevance of conformation for the antigenicity of disulfide-bonded loops of HIV-2 gp125, the antigenicity of linear and cyclic peptides was tested against a set of 76 HIV-2 positive human sera by enzyme-linked immunosorbent assay. Peptides 2, 4 and 9, mimicking the V1, V2 and V3 regions of the external envelope glycoprotein (gp 125) of HIV-2, were the most highly reactive with HIV-2 positive human sera tested at the dilution of 1:50. Cyclic peptides generally were recognized more than linear peptides, as shown by their greater inhibition (2 to 10 times more) of antigen-antibody complexes. Structure-antigenicity of peptide V3, the most reactive peptide (75% of the HIV-2 positive sera tested), was analyzed further. Cyclic peptide 9C had a higher affinity for anti-gp125 antibodies than linear peptide 9L. In addition, circular dichroism showed that linear and cyclic peptides 9 had a similar structure, but when analyzed in aqueous solution or in trifluoroethanol (TFE), the structural difference shown with antibodies was not confirmed. No significant difference was observed between the antigenicity of linear and cyclic peptides 1, 8 and 11, mimicking the C1, C2 and C4 regions of HIV-1 gp125. These peptides were weakly reactive with HIV-2 positive sera. This result agrees with the low immunogenicity of conserved regions.
...
PMID:Antigenicity of linear and cyclic peptides mimicking the disulfide loops in HIV-2 envelope glycoprotein: synthesis, reoxidation and purification. 960 17

Tyr183 is a constituent of the highly conserved YXDD motif common to all retroviral reverse transcriptases. The two aspartates in this motif are the crucial members of the catalytic carboxylate triad while residue X, which in the case of HIV-1 RT is Met184, is implicated in dNTP substrate recognition and fidelity of DNA synthesis. In an attempt to understand the function of Tyr183 in the catalytic mechanism, we generated mutants of this residue (Y183F and Y183A) and subjected them to in-depth analysis. The efficiency of reverse transcription of natural U5-PBS HIV-1 RNA template was severely impaired by both the conservative and nonconservative substitutions. The major defect identified was at the level of dNTP binding as determined by a 20-80-fold increase in the Km for the dNTP substrate on both homopolymeric and heteropolymeric RNA and DNA templates. A significant reduction in processivity of DNA synthesis by these mutants was also noted. However, the fidelity of DNA synthesis by the Y183F and Y183A mutants was increased significantly compared to the wild-type enzyme. Interestingly, the reduction in the polymerase activity due to single substitution of Tyr to Phe in the YMDD motif is compensated by a second substitution of Met to Val in the same motif, herein referred to as the FVDD. The loss of dNTP binding as well as decreased processivity of DNA synthesis exhibited by the Y183F mutant was also compensated by mutation at the second site. Curiously, the double mutant did not exhibit any synergistic effect in regard to fidelity of DNA synthesis as might be expected since both the single mutations (Y183F, M184V) exhibited enhanced fidelity compared to the wild-type enzyme. These data implicate Tyr183 and Met184 as important constituents of the dNTP-binding pocket. We propose a model which suggests that subtle structural changes due to mutation in the flexible beta9-beta10 loop region at the active site of the molecule influence the enzyme activity and substrate recognition.
...
PMID:Loss of polymerase activity due to Tyr to Phe substitution in the YMDD motif of human immunodeficiency virus type-1 reverse transcriptase is compensated by Met to Val substitution within the same motif. 965 75

Certain aspects of the clinical syndrome of dementia, cerebral atrophy, predominantly sensory neuropathy, and vacuolar myelopathy in AIDS resemble those seen in vitamin B12 deficiency. Pathologically, there are similarities not only in the changes in the spinal cord, but also in the brain and peripheral nerves. The pathogenesis of vacuolar myelopathy may be secondary to a combination of immune mediated myelin and oligodendrocyte injury, and simultaneous impairment of repair mechanisms due to a deficiency of S-adenosylmethionine (SAM). Products derived from macrophages may interfere directly with the methyl transfer cycle through the generation of reactive oxygen intermediates and reactions involving nitric oxide and peroxynitrite which may limit the supply of methionine for conversion to SAM, both by direct interaction as well as through inhibition of methionine synthase. Macrophage activation with secretion of cytokines and other biologically reactive substances within the nervous system is sustained in the late stages of HIV infection by the general effects of immune depletion, including loss of T cells (with concomitant reduction of macrophage regulatory molecules) and recurrent opportunistic infections, and may be further augmented by the local presence of the virus itself (or its surface glycoprotein gp120). This would account for the common, but not exclusive, occurrence of vacuolar myelopathy in AIDS. The ability of the virus and its products to stimulate macrophage and microglial activation may also explain the association between severity of vacuolar myelopathy and the presence of HIV encephalitis. A similar mechanism may underlie the pathogenesis of dementia, cerebral atrophy, and peripheral neuropathy. Local factors or differential susceptibility between the central and peripheral nervous system may determine whether myelinotoxic or neurotoxic processes predominate; the prominence of myelin involvement in the spinal cord, and axonal involvement peripherally may reflect both ends of this range, with the brain manifesting a more equal balance of both processes.
...
PMID:Hypothesis on the pathogenesis of vacuolar myelopathy, dementia, and peripheral neuropathy in AIDS. 1020 45

A minimal, nonamer epitope (TEMEKEGKI) from the reverse transcriptase protein of HIV-1, restricted by H-2Kk, was identified and the function of individual residues determined. Besides classical anchor residues at positions 2 and 9, methionine at position 3 was identified as an important MHC anchor and improved binding of a different (malarial) nonamer epitope to H-2Kk, albeit while also abolishing CTL recognition. Lysine at position 5 was replaceable by alanine for CTL raised against wild-type peptide but abolished recognition for CTL raised against the variant 5ALA peptide, indicating a unidirectional cross-reactivity. Interestingly, one CTL line raised against the 5ALA substituted peptide was permissive for a double substitution at positions 5 and 6, in which lysine was permissive at position 5 only if the adjacent glutamic acid was replaced by alanine. Extensive analysis revealed three distinct patterns of responses with peptides doubly substituted in this region: recognition of both single substitutions but not the double substitution, recognition of only one single substitution but also the double substitution, or recognition of both single substitutions and the double substitution. A second complementary substitution can therefore restore function lost through a first substitution. Thus, no residue acts independently of its neighbors, and pairs of substitutions may give results not predictable from the effects of each taken singly. This finding may have bearing on viral infections (such as HIV), in which the accumulation of two mutations in the epitope may lead to the reengagement of memory CTL previously silenced by the initial mutation.
...
PMID:The importance of pairwise interactions between peptide residues in the delineation of TCR specificity. 979 3

Human immunodeficiency virus type 1 (HIV-1) exclusively uses tRNA3Lys to initiate reverse transcription. A novel HIV-1 mutant which stably utilizes tRNAMet rather than tRNA3Lys as a primer was previously identified [HXB2(Met-AC] (S.-M. Kang, Z. Zhang, and C. D. Morrow, J. Virol. 71:207-217, 1997). Comparison of RNA secondary structures of the unique sequence (U5)-primer binding site (PBS) viral RNA genome alone or complexed with tRNAMet of HXB2(Met-AC) revealed structural motifs in common with the U5-PBS of the wild-type virus. In the current study, mutations were constructed to alter the U5-PBS structure and disrupt the U5-PBS-tRNAMet interaction of the virus derived from HXB2(Met-AC). All of the mutant viruses were infectious following transfection and coculture with SupT1 cells. Analysis of the initiation of reverse transcription revealed that some of the mutants were impaired compared to HXB2(Met-AC). The genetic stability of the PBS from each virus was determined following in vitro culture. Two mutant proviral constructs, one predicted to completely disrupt the stem-loop structure in U5 and the other predicted to destabilize contact regions of U5 with tRNAMet, reverted back to contain a PBS complementary to tRNA3Lys. All other mutants maintained a PBS complementary to tRNAMet after in vitro culture, although all contained multiple nucleotide substitutions within the U5-PBS from the starting proviral clones. Most interestingly, a viral mutant containing a 32-nucleotide deletion between nucleotides 142 and 173, encompassing regions in U5 which interact with tRNAMet, maintained a PBS complementary to tRNAMet following in vitro culture. All of the proviral clones recovered from this mutant, however, contained an additional 19-nucleotide insertion in U5. RNA modeling of the U5-PBS from this mutant demonstrated that the additional mutations present in U5 following culture restored RNA structures similar to those modeled from HXB2(Met-AC). These results provide strong genetic evidence that multiple sequence and structural elements in U5 in addition to the PBS are involved in the interaction with the tRNA used for initiation of reverse transcription.
...
PMID:Genetic analysis of a unique human immunodeficiency virus type 1 (HIV-1) with a primer binding site complementary to tRNAMet supports a role for U5-PBS stem-loop RNA structures in initiation of HIV-1 reverse transcription. 997 59

Tyrosine 222 of MuLV RT is an invariant residue of the highly conserved YXDD motif in the reverse transcriptase class of enzymes. The residue X is Met 184 in HIV-1 RT and Val 223 in MuLV RT. This residue has been implicated in the fidelity of DNA synthesis, whereas the role of the preceding tyrosine in this aspect, as well as in the catalytic mechanism of MuLV RT, remains to be elucidated. We have substituted Tyr 222 with Phe, Ser, and Ala by site-directed mutagenesis and have characterized the properties of the individual mutant enzymes. The results show that Tyr-->Phe substitution did not affect the polymerase activity of the enzyme, while Tyr-->Ser and Tyr-->Ala substitutions significantly reduced the polymerase activity. The pyrophosphorolysis activities of these mutants showed the same trend as the polymerase activities, suggesting an essential role for Y222 in the catalytic mechanism of MuLV RT. One of the most interesting observations of Y-->F substitution was the significantly increased fidelity of DNA synthesis on RNA templates. In addition, a limited extent of ribonucleotide incorporation on RNA template that was consistently noted with the wild-type enzyme was reduced with the Y222F mutant. The resistance to all four ddNTPs, however, persisted in the wild type and Y222 mutants on the RNA template. A ternary complex model of MuLV RT shows that (a) the aromatic ring of Tyr/Phe is positioned between the terminal and penultimate primer bases and (b) the phenolic OH group is seen within hydrogen bonding distance with the base moieties of two template and penultimate primer nucleotides. We propose that the base stacking interaction of Tyr 222 stabilizes the primer terminus position which is essential for the catalytic reaction. However, the weaker stacking interaction of Y compared to F, due to polarization of the pi-charge toward the phenoxyl-OH as well as the resonating character of its H-bond center, may provide slight flexibility to the position of the template base which may be responsible for the error-proneness of MuLV RT.
...
PMID:Tyrosine 222, a member of the YXDD motif of MuLV RT, is catalytically essential and is a major component of the fidelity center. 1005 31

Chemokines were originally isolated based on their abilities to selectively attract and recruit leukocyte populations. Over the last few years there has been an explosion in the number of new chemokines identified, and as a result many receptors previously considered to be orphans have now been paired up with their ligands. Here we review some of the latest results in this area, illustrating with data from our laboratory. The central question from a drug discovery perspective, is to show whether inhibiting chemokine receptors leads to a change in disease status. Although we are still a long way from having candidate molecules to take into the clinic, a flavour of what may be possible can be inferred from mutant chemokines with antagonistic properties. We discuss recent data using two of these proteins, Met-RANTES which has anti-inflammatory properties, and AOP-RANTES which has been shown to prevent infection of macrophages and T-cells by M-tropic HIV strains.
...
PMID:Chemokine receptors and their role in leukocyte activation. 1006 24

The CC-chemokine receptor 5 (CCR5) mediates activation of T lymphocytes and macrophages by chemokines and is a major co-receptor for macrophage-tropic HIV-1 strains. Recently, it was shown that the natural CCR5 ligands RANTES, macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and amino-terminal modifications of RANTES (Met-RANTES, AOP-RANTES) significantly differ in their abilities to induce sequestration of CCR5 from cellular surfaces. It was hypothesized that these findings may account for the observed differences between these molecules to inhibit HIV infectivity in vitro. Herein we review our work on early regulatory mechanisms that are initiated by ligand binding to CCR5 and that, conceptually, are involved in receptor endocytosis. A better understanding of these mechanisms may provide new therapeutic strategies to prevent HIV infection.
...
PMID:Chemokine-induced phosphorylation of CC chemokine receptor 5 (CCR5). 1008 May 28

<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>