Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT00572 (Asn)
 11,732 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mutations of human immunodeficiency virus type 1 (HIV-1) protease at four positions, Val82, Asp30, Gly48, and Lys45 were analyzed for the resulting effects on kinetics and inhibition. In these mutants, Val82 was substituted separately by Asn, Glu, Ala, Ser, Asp, and Gln; Asp30 was individually substituted by Phe or Trp; Gly48 by His, Asp, and Tyr, respectively; and Lys45 by Glu. By examination of the inhibition of a single inhibitor, the differences in Ki values between the native and mutant enzymes can range from very large to insignificant even for the mutants with substitutions at the same position. By examination of a single mutant enzyme, the same broad range of Ki changes was observed for a group of inhibitors: Thus, how much the inhibition changes from the wild-type enzyme to a mutant is dependent on both the mutation and the inhibitor. The examination of Ki changes of inhibitors with closely related structures binding to Val82 mutants also reveals that the change of inhibition involves subsites in which Val82 is not in direct contact, indicating a considerable flexibility of the conformation of HIV protease. For the catalytic activities of the mutants, the kcat and Km values of many Val82 mutants and a Lys45 mutant are comparable to the native enzyme. Surprisingly, Gly48 mutations produce enzymes with catalytic efficiency superior to that of the wild-type enzyme by as much as 10-fold. Modeling of the structure of the mutants suggests that the high catalytic efficiency of some substrates is related to an increase of rigidity of the flap region of the mutants. The examination of the relative changes of inhibition and catalysis of mutants suggests that some of the Val82 and Gly48 mutants are potential resistance mutants. However, the resistance is specific with respect to individual inhibitors.
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PMID:Effect of point mutations on the kinetics and the inhibition of human immunodeficiency virus type 1 protease: relationship to drug resistance. 782 64

The human immunodeficiency virus, HIV-1, is generally accepted to be responsible for AIDS. It is imperative that all approaches, empirical and rational, be taken for development of a drug for therapy of this disease. These approaches are discussed, with emphasis on the direction being pursued in our laboratory. Empirically, we found 3'-deoxy-2',3'-didehydrothymidine, a compound first synthesized for potential anticancer activity by J. Horwitz in the 1960s, to be a potent inhibitor of HIV-1. It is now in Phase II/III clinical trials. We have also synthesized several 2,5'-anhydro pyrimidine nucleoside analogs, which have interesting chemical and biological properties. We have evaluated a natural product, gossypol and synthesized various derivatives for anti-HIV-1 activity, but none were appreciably more inhibitory than the parent compound. More recently, we have taken the rational approach and synthesized a boron-modified tetrapeptide, Ac-Thr-Leu-Asn-boro-Phe, which corresponds to the COOH-terminal of the Phe-Pro scissle bond of the gag/pol gene polyprotein product. Potent inhibition of the HIV-1 encoded protease was observed. These approaches and findings will be discussed.
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PMID:Empirical and rational approaches for development of inhibitors of the human immunodeficiency virus--HIV-1. 802 62

In human immunodeficiency virus, RNA selection and packaging during assembly involve the two retroviral-type fingers of the nucleocapsid protein that are held in a constrained configuration by coordinated zinc ions. In this report, we demonstrate that the nucleocapsid protein in a metal bound state is resistant to cleavage by the viral protease, but upon removal of zinc ions by chelating agents, it is hydrolyzed within the first zinc finger between Phe-16 and Asn-17. However, 3-nitrosobenzamide and cupric ions, which release zinc through oxidation of the cysteine residues of the finger, render the nucleocapsid protein resistant to cleavage. Since protease inhibitors and 3-nitrosobenzamide restrict processes relating to steps early in infection, the cleavage of the nucleocapsid protein may represent an essential event that can be exploited for the design of novel antiviral agents.
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PMID:Removal of zinc is required for processing of the mature nucleocapsid protein of human immunodeficiency virus, type 1, by the viral protease. 807 14

To examine the role of the glycans of human immunodeficiency virus type 1 transmembrane glycoprotein gp41, conserved glycosylation sites within the env sequence (Asn-621, Asn-630, and Asn-642) were mutated to Gln. The mutated and control wild-type env genes were introduced into recombinant vaccinia virus and used to infect BHK-21 or CD4+ CEM cells. Mutated gp41 appeared as a 35-kDa band in a Western blot (immunoblot), and it comigrated with the deglycosylated form of wild-type gp41. Proteolytic cleavage of the recombinant wild-type and mutant forms of the gp160 envelope glycoprotein precursor was analyzed by pulse-chase experiments and enzyme-linked immunosorbent assay: gp160 synthesis was similar whether cells were infected with control or mutated env-expressing recombinant vaccinia virus, but about 10-fold less cleaved gp120 and gp41 was produced by the mutated construct than the control construct. The rates of gp120-gp41 cleavage at each of the two potential sites appeared to be comparable in the two constructs. By using a panel of antibodies specific for gp41 and gp120 epitopes, it was shown that the overall immunoreactivities of control and mutated gp41 proteins were similar but that reactivity to epitopes at the C and N termini of gp120, as present on gp160 produced by the mutated construct, was enhanced. This was no longer observed for cleaved gp120 in supernatants. Both gp120 proteins, from control and mutated env, were expressed on the cell surface under a cleaved form and could bind to membrane CD4, as determined by quantitative immunofluorescence assay. In contrast, and despite sufficient expression of env products at the cell membrane, gp41 produced by the mutated construct was unable to induce membrane fusion. Therefore, while contradictory results reported in the literature suggest that gp41 individual glycosylation sites are dispensable for the bioactivity and conformation of env products, it appears that such is not the case when the whole gp41 glycan cluster is removed.
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PMID:Functional role of the glycan cluster of the human immunodeficiency virus type 1 transmembrane glycoprotein (gp41) ectodomain. 809 18

The substrate specificity of the Moloney murine leukemia virus protease (Mo-MuLV PR) was analyzed by using the oligopeptide substrate Val-Ser-Gln-Asn-Tyr decreases Pro-Ile-Val-Gln-NH2 and a series of analogs containing single amino acid substitutions in the P4-P3' positions. Mo-MuLV PR appears to act similarly to the human immunodeficiency virus (HIV) PRs, except for peptides having substitutions at P4 and P2 positions. Mo-MuLV PR shows a strong preference for the analogs having hydrophobic residues, such as Val or Ile at P4, and Ile and Leu at P2, in contrast to HIV-1 and HIV-2 PRs, which prefer smaller or more polar residues at both positions. We built a molecular model of Mo-MuLV PR on the basis of the crystal structure of the related HIV PR. Although the overall structure of Mo-MuLV PR is predicted to be close to that of HIV-1 PR, almost all of the residues forming the subsites are different. The increased hydrophobicity due to the Pro12 insertion and the presence of more aromatic residues in the S4 subsite of Mo-MuLV PR compared to HIV-1 and HIV-2 PRs can be correlated with the observed differences using P4-substituted analogs of VSQNYPIVQ. The preference of Mo-MuLV PR for larger hydrophobic residues at the P2 position can be correlated with the larger size of its S2 subsite, due in part to the presence of Val39, Ala57, and His84 in Mo-MuLV PR, instead of Ile32, Ile50, and Met76, respectively, as occurs in HIV-2 PR.
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PMID:Kinetic and modeling studies of subsites S4-S3' of Moloney murine leukemia virus protease. 820 3

The transmembrane envelope glycoprotein (gp41) of human immunodeficiency virus type 1 possesses four consensus sites (Asn-X-Ser/Thr) for the incorporation of N-linked sugars situated on the extracellular domain of the molecule. The purpose of this investigation was to determine the significance of each of these sites in relation to the structure and function of the viral envelope glycoprotein. Each of the four sites was removed by in vitro mutagenesis of gp160 sequence in the non-infectious viral clone pEVd1443, so that amino acids 616, 621, 642 and 679 were each changed from asparagine to serine. The effects of mutagenesis were assessed by syncytium assay after wild-type or mutant envelope clones had been transfected into CD4+ HeLa cells. Removal of the glycosylation site at position 642 resulted in the synthesis of precursor gp160 that was neither cleaved, to give gp120 and gp41, nor transported to the plasma membrane of transfected cells. A consequence of these events was that envelope mutant 642 failed to induce syncytia between neighbouring cells in which it had been expressed. The results of this study indicate that N-linked glycosylation of Asn-642 in the glycoprotein produced by the pEVd1443 expression system is necessary for the correct intracellular processing of gp160 to yield surface-expressed, fusogenic gp41.
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PMID:Deletion of a single N-linked glycosylation site from the transmembrane envelope protein of human immunodeficiency virus type 1 stops cleavage and transport of gp160 preventing env-mediated fusion. 820 3

Using the process of "antibody antigenization," we engineered two antibody molecules carrying in the third complementarity-determining region of the heavy chain variable domain a 7-mer or a 15-mer peptide epitope of the first extracellular domain (D1) of human CD4 receptor--namely, Ser-Phe-Leu-Thr-Lys-Gly-Pro-Ser (SFLTKGPS; positions 42 through 49) and Gly-Ser-Phe-Leu-Thr-Lys-Gly-Pro-Ser-Lys-Leu-Asn-Asp-Arg-Ala (GSFLTKGPSKLNDRA; positions 41 through 55). These amino acid sequences are contained in the consensus binding site for the human immunodeficiency virus (HIV) on CD4 receptor. Both antigenized antibodies (AgAbs) bound recombinant gp120 and were recognized by a prototype monoclonal antibody to CD4 whose binding site is within amino acid residues 41-55. AgAbs were then used as immunogens in rabbits and mice to elicit a humoral response against CD4. Only the AgAb carrying the sequence 41GSFLTKGPSKLN-DRA55 induced a response against CD4. The induced antibodies showed specificity for the amino acid sequence of CD4 engineered in the AgAb molecule, were able to inhibit the formation of syncytia between human CD4+ T cells MOLT-3 and 8E5 (T cells that are constitutively infected with HIV), and stained human CD4+ CEM T cells. Four murine monoclonal antibodies were used to analyze the relationship between syncytia inhibition and CD4 binding at the single antibody level, and indicated that recognition of native CD4 is not an absolute requirement for inhibition of syncytia. This study demonstrates that antigenized antibodies can be used as immunogens to elicit site-specific and biologically active immunity to CD4. The importance of this approach as a general way to induce anti-receptor immunity and as a possible new measure to immunointervention in HIV infection is discussed.
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PMID:Active immunity against the CD4 receptor by using an antibody antigenized with residues 41-55 of the first extracellular domain. 826 9

In order to investigate the relationships between the three-dimensional structure and the enzymic activity of E. coli RNase HI, three mutant proteins, which were completely inactivated by the replacements of three functional residues, Asp10 by Asn (D10N), Glu48 by Gln (E48Q), and Asp70 by Asn (D70N), were crystallized. Their three-dimensional structures were determined by x-ray crystallography. Although the entire backbone structures of these mutants were not affected by the replacements, very localized conformational changes were observed around the Mg(2+)-binding site. The substitution of an amide group for a negatively charged carboxyl group in common induces the formation of new hydrogen bond networks, presumably due to the cancellation of repulsive forces between carboxyl side chains with negative charges. These conformational changes can account for the loss of the enzymic activity in the mutants, and suggest a possible role for Mg2+ in the hydrolysis. Since the 3 replaced acidic residues are completely conserved in sequences of reverse transcriptases from retroviruses, including human immunodeficiency virus, the concepts of the catalytic mechanism deduced from this structural analysis can also be applied to RNase H activity in reverse transcriptases.
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PMID:Crystal structures of ribonuclease HI active site mutants from Escherichia coli. 840 67

The atomic structure of a truncated glycoprotein gp120 from human immunodeficiency virus 1 (HIV-1) that contains the principal neutralizing antigenic sites and the CD4 binding domain has been derived by molecular dynamics and calculation of potential energy using the DREIDING force field. The resultant N-glycosylated molecular model is consistent with known properties of gp120 and docks with CD4 with a substantial reduction in the sum of the internal potential energies of the individual proteins (delta E = -200 kcal/mol). The primary mechanism of recognition and binding is the insertion of the solvent-accessible Phe-43 of CD4 into a gp120 solvent-accessible acceptor pit formed by Trp-427, Tyr-435, and the high-mannose oligosaccharide N-linked to Asn-230. delta E for the nonglycosylated complex is reduced significantly (-75 kcal/mol). Binding is by pi-pi* interactions of the aromatic groups forming a hydrophobic, thermodynamically stable environment for these functional noncovalent bonding participants. This model for gp120 provides a theoretical basis for the evaluation of HIV molecular pathogenesis involving the env proteins, the analysis of conformation on functional immune response of the host, and the design of nonproteinaceous inhibitors specific for the CD4 binding site on gp120.
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PMID:Proposed atomic structure of a truncated human immunodeficiency virus glycoprotein gp120 derived by molecular modeling: target CD4 recognition and docking mechanism. 848 33

Hydrosoluble macromolecular fluorogenic substrates specific for the human immunodeficiency virus 1 (HIV-1) proteinase have been prepared. The fluoresceinyl peptide Ftc-epsilon-Ahx-Ser-Phe-Asn-Phe-Pro-Gln-Ile-Thr-(Gly)n, corresponding to the first cleavage site of HIV-1 gag-pol native precursor was linked to a water-soluble neutral (Lys)n derivative. The epsilon-aminohexanoyl residue (epsilon-Ahx) and the glycyl sequence were added in order to improve the stability of the substrate and the accessibility of the cleavage site to the HIV-1 proteinase respectively. This macro-molecular peptidic-substrate conjugate is significantly more water-soluble than the free peptide itself on a substrate molar concentration basis. The assay is based on the quantitative precipitation of the polymeric material by adding propan-2-ol whereas the fluorescent peptide moiety released upon proteolysis remains soluble in the supernatant. The proteinase activity is assessed by measuring the fluorescence of the supernatant. This assay allows the detection of a few fmol of HIV-1 proteinase, even in the presence of cell culture media, plasma or cell lysate and it gives accurate results within a large proteinase concentration range. The hydrosoluble macromolecular substrate is also suitable for determining the HIV-1 proteinase activity using 96-well microplates, allowing us to test accurately and rapidly numerous enzyme samples and/or the potency of new proteinase inhibitors.
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PMID:Sensitive, hydrosoluble, macromolecular fluorogenic substrates for human immunodeficiency virus 1 proteinase. 848 13


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