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 most preferred residue in the substrates of human immunodeficiency virus (HIV-1) protease is glutamic acid in the P2' position. The catalytic importance of this charged residue has been studied to obtain a detailed insight into the mechanism of action, which will promote drug design to combat the virus. To this end, we have synthesized Lys-Ala-Arg-Val-Leu*Phe(NO2)-Glu-Ala-Nle (substrate E) and its counterpart containing the neutral Gln (substrate Q) in place of Glu. Kinetic analyses have shown that the specificity rate constants (kcat/Km) display bell-shaped pH dependencies for both substrates, but the pH-independent limiting value is 35-40-fold higher with substrate E than with substrate Q. In contrast to the pH-rate profiles of kcat/Km, there is a striking difference between the pH dependencies of Km and kcat for the two substrates. This indicates different ground state and transition state stabilizations in the two reactions. Solvent kinetic deuterium isotope effects show that the rate-limiting step for the hydrolysis of substrate E is a chemical step coupled with proton transfer whereas with substrate Q it is a physical step, presumably a conformational change. Accordingly, the charged residue in P2' alters the rate-limiting step and the nature of the enzyme-substrate complex, resulting in different mechanisms for the two substrates.
...
PMID:Substrate-dependent mechanisms in the catalysis of human immunodeficiency virus protease. 804 36

Previous studies on the role of specific residues of the peptide or MHC molecule in Ag presentation have revealed the sensitivity of this complex system to even small changes in structure. In our study, we have analyzed the effect of amino acid substitution in a major CD4+ T cell determinant (T1) of HIV-1 gp160 on binding and recognition in the context of various E alpha E beta MHC class II molecules. Individual alanine substitutions at all but three positions had little or no negative effect on either MHC binding or recognition by a specific T hybridoma, whereas substitutions with larger side chains often diminished reactivity. A poly-alanine peptide containing only four of the original residues was an effective MHC class II binder and in vivo immunogen, although lacking the ability to stimulate the hybridoma. Replacement of a glutamic acid in T1 with alanine or a size-conservative, uncharged glutamine, but not a negatively charged aspartic acid produced a peptide at least 100-fold more potent than the parent peptide, indicating an inhibitory effect of the negative charge. Conversely, substitution of a glutamic acid for valine at position 29 in the floor of the peptide binding site of the E alpha E beta molecule decreased functional presentation of this peptide by more than 2 logs. However, these two effects of glutamic acid were not complementary and were mediated by distinct mechanisms, as the change in the peptide altered the extent of binding to class II, but the change in the MHC molecule decreased recognition without inhibiting peptide binding. Taken together, the data all suggest the conclusion that changes in side-chains of peptides and MHC molecules affect Ag presentation and T cell stimulation most often by introducing dominant negative or interfering groups that prevent or alter the pattern of binding events primarily mediated by a very limited number of other residues in the Ag or presenting molecule. These results have important implications for understanding the biochemistry of peptide-MHC-TCR interactions and for the possible design of vaccines both more potent and less subject to allele-specific limitations on immunogenicity.
...
PMID:The importance of dominant negative effects of amino acid side chain substitution in peptide-MHC molecule interactions and T cell recognition. 809 57

Bacteriophage 434 repressor recognizes the operator sequences ACAAG and ACAAT. As the same or similar sequences occur in the enhancer region of HIV-1, 434 repressor was a potential HIV enhancer-binding protein. We found that the interaction of the DNA-binding domain of 434 repressor with a 57-bp HIV enhancer DNA was very weak whereas a 42-residue construct, comprising the recognition helix and four copies of a positively charged segment of the repressor, bound strongly. The results of footprint and cell-free in vitro transcription studies showed that the 42-residue peptide bound preferably to the enhancer region of HIV-1 and acted as an artificial repressor. Replacement of an essential glutamine of the recognition helix by glutamic acid resulted in a partial shift of the sequence specificity of the 42-residue peptide.
...
PMID:The DNA-binding properties of an artificial 42-residue polypeptide derived from a natural repressor. 841 11

HBY 097 [(S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3, 4-dihydroquinoxaline-2(1H)-thione] was selected from a series of quinoxalines as a nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (NNRTI). HBY 097 was shown to be a highly potent inhibitor of HIV-1 induced cell killing and HIV-1 replication in a variety of human cell lines as well as in fresh human peripheral blood lymphocytes and macrophages. The compound was also active against a variety of clinical isolates of HIV-1 including different HIV-1 subtypes and viruses resistant to 3'-deoxy-3'-azidothymidine. Mutant reverse transcriptases which arise as a consequence of treatment with other nonnucleoside inhibitors of HIV-1 reverse transcriptase were still inhibited by HBY 097 at relatively low concentrations. An HIV-1MN variant resistant to inhibition by HBY 097 displayed in the reverse transcriptase gene a mutation causing a substitution at position 190 of a glutamic acid for a glycine residue (G190 --> E), which is characteristic for quinoxaline derivatives. The drug was demonstrated to possess a favorable toxicity profile and to show good oral bioavailability in both mice and dogs. As a consequence of its outstanding properties, HBY 097 was selected for further development and is at present undergoing clinical trials.
...
PMID:Preclinical evaluation of HBY 097, a new nonnucleoside reverse transcriptase inhibitor of human immunodeficiency virus type 1 replication. 861 78

We describe a single method to purify milligram amounts of authentic wild-type and mutant HIV-1 and HIV-2 Tat proteins overexpressed in Escherichia coli. This method takes advantage of the highly basic, positively charged RNA binding domain present in both HIV-1 and HIV-2 Tat, which also facilitated purification of HIV-1 and HIV-2 mutant Tat proteins. In contrast to previously described methods, our method does not require use of denaturing or reducing agents, since Tat is present in the soluble fraction after bacterial lysis. The activity of purified wild-type and mutant HIV-1 and HIV-2 Tat proteins was determined using cell-based uptake, in vitro transcription, and TAR binding assays. As expected, both HIV-1 and HIV-2 Tat efficiently transactivated the HIV-2 LTR, whereas HIV-2 Tat transactivated the HIV-1 LTR less efficiently than HIV-1 Tat. Purified HIV-2 Tat proteins in which the glutamic acid residue at position 77 was changed to either glycine or glutamine transactivated the HIV-1 LTR more efficiently than wild-type Tat-2, providing additional evidence that the net charge of this region may be responsible for nonreciprocal transactivation between Tat-1 and Tat-2. Our results demonstrate that this method can be used to rapidly purify authentic wild-type and mutant Tat proteins which are suitable for cell-based and in vitro functional studies.
...
PMID:Purification and functional characterization of wild-type and mutant HIV-1 and HIV-2 Tat proteins expressed in Escherichia coli. 881 70

HIV-1 and HIV-2 proteinases (PR) are responsible for the processing of viral polyproteins, a step that is crucial for the formation of infectious virus particles. PR represents one of the most important targets for antiviral chemotherapy. Inhibitors of HIV-1 PR usually exhibit a 10- to 100-fold weaker affinity for HIV-2 PR. In order to design subnanomolar inhibitors for both HIV-1 and HIV-2 PRs, we prepared a series of compounds varying in the type of scissile bond replacement as well as in the P1, P1', and P2' side chains. While inhibitors containing reduced amide, hydroxyethylamine and statine isosteres had Ki values in the range of 10(-10)-10(-9) M against HIV-1 PR; their activities against HIV-2 PR were several orders of magnitude lower. Glutamic acid was identified to be the optimal P2' residue for both PRs. HIV-2 PR was shown to be more sensitive to P2' Glu-->Gln replacement. Using this data set we were able to design and prepare hydroxyethylene isostere containing inhibitors that were equipotent against both PRs.
...
PMID:Potency comparison of peptidomimetic inhibitors against HIV-1 and HIV-2 proteinases: design of equipotent lead compounds. 914 53

Although the Nef proteins encoded by human immunodeficiency virus type 1 (HIV-1) and simian immuno-deficiency virus (SIV) are known to induce the efficient internalization and degradation of cell surface CD4, it remains unclear whether this process involves a direct interaction between Nef and CD4. Here, we report that CD4 downregulation by HIV-1 and SIV Nef requires distinct but overlapping target sites within the CD4 intracytoplasmic domain. In particular, mutation of a glutamic acid residue located at CD4 residue 405 or of arginine and methionine residues located, respectively, at residue 406 and 407 results in a mutant CD4 protein that is efficiently downregulated by HIV-1 Nef but refractory to downregulation by SIV Nef. However, both HIV-1 and SIV Nef require an isoleucine located at residue 410 and the dileucine motif found at CD4 residues 413 and 414. CD4 downregulation induced by the Nef protein encoded by HIV-2 is shown to require a CD4 target sequence that is similar to, but distinct from, that observed with SIV Nef. These data explain the previous finding that the murine CD4 protein, which has an alanine at residue 405, is refractory to downregulation by SIV, but not HIV-1, Nef (J. L. Foster, S.J. Anderson, A. L. B. Frazier, and J. V. Garcia, Virology 201:373-379, 1994). In addition, these observations provide strong genetic support for the hypothesis that the Nef-mediated downregulation of cell surface CD4 requires a direct Nef-CD4 interaction.
...
PMID:Human immunodeficiency virus types 1 and 2 and simian immunodeficiency virus Nef use distinct but overlapping target sites for downregulation of cell surface CD4. 926 98

Short peptides corresponding to the arginine-rich domains of several RNA-binding proteins are able to bind to their specific RNA sites with high affinities and specificities. In the case of the HIV-1 Rev-Rev response element (RRE) complex, the peptide forms a single alpha-helix that binds deeply in a widened, distorted RNA major groove and makes a substantial set of base-specific and backbone contacts. Using a reporter system based on antitermination by the bacteriophage lambda N protein, it has been possible to identify novel arginine-rich peptides from combinatorial libraries that recognize the RRE with affinities and specificities similar to Rev but that appear to bind in nonhelical conformations. Here we have used codon-based mutagenesis to evolve one of these peptides, RSG-1, into an even tighter binder. After two rounds of evolution, RSG-1.2 bound the RRE with 7-fold higher affinity and 15-fold higher specificity than the wild-type Rev peptide, and in vitro competition experiments show that RSG-1.2 completely displaces the intact Rev protein from the RRE at low peptide concentrations. By fusing RRE-binding peptides to the activation domain of HIV-1 Tat, we show that the peptides can deliver Tat to the RRE site and activate transcription in mammalian cells, and more importantly, that the fusion proteins can inhibit the activity of Rev in chloramphenicol acetyltransferase reporter assays. The evolved peptides contain proline and glutamic acid mutations near the middle of their sequences and, despite the presence of a proline, show partial alpha-helix formation in the absence of RNA. These directed evolution experiments illustrate how readily complex peptide structures can be evolved within the context of an RNA framework, perhaps reflecting how early protein structures evolved in an "RNA world."
...
PMID:Molding a peptide into an RNA site by in vivo peptide evolution. 934 32

The CC-chemokine receptor CCR5 is required for the efficient fusion of macrophage (M)-tropic human immunodeficiency virus type 1 (HIV-1) strains with the plasma membrane of CD4+ cells and interacts directly with the viral surface glycoprotein gp120. Although receptor chimera studies have provided useful information, the domains of CCR5 that function for HIV-1 entry, including the site of gp120 interaction, have not been unambiguously identified. Here, we use site-directed, alanine-scanning mutagenesis of CCR5 to show that substitutions of the negatively charged aspartic acid residues at positions 2 and 11 (D2A and D11A) and a glutamic acid residue at position 18 (E18A), individually or in combination, impair or abolish CCR5-mediated HIV-1 entry for the ADA and JR-FL M-tropic strains and the DH123 dual-tropic strain. These mutations also impair Env-mediated membrane fusion and the gp120-CCR5 interaction. Of these three residues, only D11 is necessary for CC-chemokine-mediated inhibition of HIV-1 entry, which is, however, also dependent on other extracellular CCR5 residues. Thus, the gp120 and CC-chemokine binding sites on CCR5 are only partially overlapping, and the former site requires negatively charged residues in the amino-terminal CCR5 domain.
...
PMID:Amino-terminal substitutions in the CCR5 coreceptor impair gp120 binding and human immunodeficiency virus type 1 entry. 942 Feb 25

The core domain of human immunodeficiency virus type 1 (HIV-1) integrase (IN) contains a D,D(35)E motif, named for the phylogenetically conserved glutamic acid and aspartic acid residues and the invariant 35 amino acid spacing between the second and third acidic residues. Each acidic residue of the D,D(35)E motif is independently essential for the 3'-processing and strand transfer activities of purified HIV-1 IN protein. Using a replication-defective viral genome with a hygromycin selectable marker, we recently reported that a mutation at any of the three residues of the D,D(35)E motif produces a 10(3)- to 10(4)-fold reduction in infectious titer compared with virus encoding wild-type IN (A. D. Leavitt et al., J. Virol. 70:721-728. 1996). The infectious titer, as measured by the number of hygromycin-resistant colonies formed following infection of cells in culture, was less than a few hundred colonies per microg of p24. To understand the mechanism by which the mutant virions conferred hygromycin resistance, we characterized the integrated viral DNA in cells infected with virus encoding mutations at each of the three residues of the D,D(35)E motif. We found the integrated viral DNA to be colinear with the incoming viral genome. DNA sequencing of the junctions between integrated viral DNA and host DNA showed that (i) the characteristic 5-bp direct repeat of host DNA flanking the HIV-1 provirus was not maintained, (ii) integration often produced a deletion of host DNA, (iii) integration sometimes occurred without the viral DNA first undergoing 3'-processing, (iv) integration sites showed a strong bias for a G residue immediately adjacent to the conserved viral CA dinucleotide, and (v) mutations at each of the residues of the D,D(35)E motif produced essentially identical phenotypes. We conclude that mutations at any of the three acidic residues of the conserved D,D(35)E motif so severely impair IN activity that most, if not all, integration events by virus encoding such mutations are not IN mediated. IN-independent provirus formation may have implications for anti-IN therapeutic agents that target the IN active site.
...
PMID:Mutations in the human immunodeficiency virus type 1 integrase D,D(35)E motif do not eliminate provirus formation. 957 31

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