Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0021051 (immunodeficiency)
 71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Vif is a 23-kDa protein encoded by human immunodeficiency virus, type 1 (HIV-1) which is important for virion infectivity. Here, we describe the phosphorylation of HIV-1 Vif and its role in HIV-1 replication. In vivo studies demonstrated that Vif is highly phosphorylated on serine and threonine residues. To identify phosphorylation sites and characterize the Vif kinase(s), Vif was expressed in Escherichia coli and purified for use as a substrate in in vitro kinase assays. The purified Vif protein was phosphorylated in vitro on serine and threonine residues by a kinase(s) present in both cytosol and membrane fractions. Phosphorylation of Vif was stimulated by phorbol 12-myristate 13-acetate and inhibited by staurosporine and hypericin, a drug with potent anti-HIV activity. The Vif kinase(s) was resistant to inhibitors of protein kinase C, cAMP-dependent kinase, and cGMP-dependent kinase, suggesting that it is distinct from these enzymes. To identify the phosphorylation sites, 32P-labeled Vif was digested by V8 protease and the peptides were resolved by reverse-phase high performance liquid chromatography. Radioactive peptide sequencing identified three phosphorylation sites within the C terminus, Ser144, Thr155, and Thr188. Two-dimensional tryptic phosphopeptide mapping indicated that these sites are also phosphorylated in vivo. Both Ser144 and Thr188 are contained in the recognition motifs (R/KXXS*/T* and R/KXXXS*/T*) used by serine/threonine protein kinases such as cGMP-dependent kinase and PKC. Ser144 is present in the motif SLQXLA, which is the most highly conserved sequence among all lentivirus Vif proteins. Mutation of Ser144 to alanine resulted in loss of Vif activity and >90% inhibition of HIV-1 replication. These studies suggest that phosphorylation of Vif by a serine/threonine protein kinase(s) plays an important role in regulating HIV-1 replication and infectivity.
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PMID:Phosphorylation of Vif and its role in HIV-1 replication. 862 71

To identify the regions that are important in human T-cell leukemia virus type 1 (HTLV-1) envelope function, we synthesized 23 kinds of peptides covering the envelope proteins and examined the inhibitory effect of each peptide on syncytium formation induced by HTLV-1-bearing cells. Of the 23 synthetic peptides, 2, corresponding to amino acids 197 to 216 on gp46 and 400 to 429 on gp21, inhibited syncytium formation induced by HTLV-1-bearing cells but did not affect syncytium formation induced by human immunodeficiency virus type 1-producing cells. The peptide concentrations giving 50% inhibition of syncytium formation for gp46 197 to 216 and gp21 400 to 429 were 14.9 and 6.0 microM, respectively. A syncytium formation assay with overlapping synthetic peptides containing amino acids 175 to 236 and 391 to 448 of the envelope proteins showed that syncytium formation was inhibited by peptides that contained the amino acid sequences 197 to 205 (Asp-His-Ile-Leu-Glu-Pro-Ser-Ile-Pro) and 397 to 406 (Gln-Glu-Gln-Cys-Arg-Phe- Pro-Asn-Ile-Thr). These observations suggest that the two regions corresponding to amino acids 197 to 216 and 400 to 429 are involved] in HTLV-1 envelope function.
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PMID:Identification and mapping of functional domains on human T-cell lymphotropic virus type 1 envelope proteins by using synthetic peptides. 862 75

The human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) contains two binding sites for the NF-kappa B/Rel family of transcription factors which are required for the transcriptional activation of viral genes by inflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha) and interleukin-1. In the present study, we examined the effect of transdominant mutants of I kappa B alpha on the synergistic activation of the HIV-1 LTR by TNF-alpha and the HIV-1 transactivator, Tat, in Jurkat T cells. The synergistic induction of HIV-1 LTR-driven gene expression represented a 50- to 70-fold stimulation and required both an intact HIV-1 enhancer and Tat-TAR element interaction, since mutations in Tat protein (R52Q, R53Q) or in the bulge region of the TAR element that eliminated Tat binding to TAR were unable to stimulate LTR expression. Coexpression of I kappa B alpha inhibited Tat-TNF-alpha activation of HIV LTR in a dose-dependent manner. Transdominant forms of I kappa B alpha, mutated in critical serine or threonine residues required for inducer-mediated (S32A, S36A) and/or constitutive (S283A, T291A, T299A) phosphorylation of I kappa B alpha were tested for their capacity to block HIV-1 LTR transactivation. I kappa B alpha molecules mutated in the N-terminal sites were not degraded following inducer-mediated stimulation (t1/2, > 4 h) and were able to efficiently block HIV-1 LTR transactivation. Strikingly, the I kappa B alpha (S32A, S36A) transdominant mutant was at least five times as effective as wild-type I kappa B alpha in inhibiting synergistic induction of the HIV-1 LTR. This mutant also effectively inhibited HIV-1 multiplication in a single-cycle infection model in Cos-1 cells, as measured by Northern (RNA) blot analysis of viral mRNA species and viral protein production. These experiments suggest a strategy that may contribute to inhibition of HIV-1 gene expression by interfering with the NF-kappa B/Rel signaling pathway.
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PMID:Transdominant mutants of I kappa B alpha block Tat-tumor necrosis factor synergistic activation of human immunodeficiency virus type 1 gene expression and virus multiplication. 870 93

Phosphorylation of proteins on serine, threonine and tyrosine is one of the significant regulatory mechanisms in gene expression and post-translational modifications in both eukaryotes and prokaryotes. Protein tyrosine phosphorylation in particular is implicated in cell proliferation, differentiation and certain pathological modifications including transformation. The overall protein tyrosine phosphorylation is modulated by protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTP). There are several viruses known to contain PTK and PTPs. A computer-based protein sequence search using the FAST P programme was used to investigate whether, theoretically, a sequence for a putative protein tyrosine phosphatase is present in the genomic sequence of the human immunodeficiency virus (HIV). A conserved motif GXGXXG characteristic of both PTK and PTP was found at the 5' LTR region of the HIV genome. Interesting sequence similarities with regulatory proteins of other retroviruses, viz. VPx of HIV-2 and X-protein of HTLV-1, and some transforming proteins were also observed. The implication of the possible phosphorylation event in association with the HIV regulatory proteins tat, rev and nef in AIDS-related malignancies is discussed.
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PMID:Tyrosine phosphorylation as a possible regulatory mechanism in the expression of human immunodeficiency virus genes. 874 91

The active human immunodeficiency virus type 1 (HIV-1) protease has a homodimeric structure, the subunits are connected by an 'interface' beta-sheet formed by the NH2- and COOH-terminal amino acid segments. Short peptides derived from these segments are able to inhibit the protease activity in the range of micromolar IC50 values. We have further improved the inhibitory power of such peptides by computer modelling. The best inhibitor, the palmitoyl-blocked peptide Pam-Thr-Val-Ser-Tyr-Glu-Leu, has an IC50 value of less than 1 microM. Some of the peptides also showed very good inhibition of the HIV-2 protease. The C-terminal segment of the HIV-1 matrix protein, Acetyl-Gln-Val-Ser-Gln-Asn-Tyr, also inhibits HIV-1 protease. Kinetic studies confirmed the 'dissociative' mechanism of inhibition by the peptides. Depending on the peptide structure and ionic strength, both dimerization inhibition and competitive inhibition were observed, as well as synergistic effects between competitive inhibitors and interface peptides.
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PMID:The inhibition of human immunodeficiency virus proteases by 'interface peptides'. 878 7

MS8209, an amphotericin B derivative blocking human immunodeficiency virus type 1 (HIV-1) entry after CD4 binding, neutralized the HIV-2 strains EHO and ROD10 but not ROD(CEM). In the V3 domain of gp120, ROD(CEM) differed from ROD10 at two positions (a threonine instead of an isoleucine at position 312 and an arginine instead of a glutamine at position 329), and drug resistance was conferred to HIV-1 by substitution of the ROD(CEM) V3 but not the ROD10 V3. V3 mutations may prevent the interaction of gp120 with MS8209 or modify the mechanism of virus entry, rendering it less accessible to neutralization.
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PMID:Possible role of the V3 domain of gp120 in resistance to an amphotericin B derivative (MS8209) blocking human immunodeficiency virus entry. 889 62

The carboxyl-terminal domain (CTD) of RNA polymerase (RNAP) II contains multiple repeats with a heptapeptide consensus: Tyr-Ser-Pro-Thr-Ser-Pro-Ser. It has been proposed that phosphorylation of this CTD facilitates clearance and elongation of transcription complexes initiated at the promoters. However, not all transcribed promoters require RNAP II with full-length CTD. Furthermore, different activators can promote capably the transcriptional activity of polymerase II mutants deleted in the CTD. Thus, the role of the RNAP II CTD in transcription and in response to activators remains incompletely understood. To study the role of CTD in the regulated transcription of human retroviruses human-T cell lymphotropic virus I and human immunodeficiency virus 1, we used an alpha-amanitin-resistant system developed previously (Gerber, H. P., Hagmann, M., Seipel, K., Georgiev, O., West, M. A., Litingtung, Y., Schaffner, W., and Corden, J. L. (1995) Nature 374, 660-662). We found that transcription directed by the human T-cell lymphotropic virus I activator protein Tax was strongly promoted by CTD-deficient RNA polymerase II. By contrast, the human immunodeficiency virus 1 activator Tat, which is recruited to the promoter by tethering to a nascent leader RNA, requires CTD-containing polymerase II for transcriptional activity. Biochemically, we characterized that Tat associated with a cellular CTD kinase activity, whereas Tax did not. Concordantly, we found that cellular transcription factor Sp1, which can activate CTD-deficient polymerase II with an efficiency similar to Tax, also failed to bind a CTD kinase. Taken together, these observations address mechanistic corollaries between activators with(out) a linked CTD kinase and regulated transcription by RNA polymerase II moieties with(out) a CTD.
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PMID:Requirements for RNA polymerase II carboxyl-terminal domain for activated transcription of human retroviruses human T-cell lymphotropic virus I and HIV-1. 891 Mar 88

The human immunodeficiency virus type-1 (HIV-1) encodes a protease which is essential for the production of infectious virus. The protease prefers substrates that contain glutamic acid or glutamine at the P2' position. The catalytic role of these residues has been studied by using a highly specific fluorogen substrate, 2-aminobenzoyl-Thr-Ile-Nle-Phe(NO2)-Gln-Arg (substrate QR), and its counterpart (substrate ER) containing Glu in place of Gln. The newly designed substrate ER that contains a pair of charged residues at P2' and P3' sites is the most specific substrate described so far for HIV-1 protease. The specificity rate constant (kcat/Km = 2.1 x 10(7) M-1 s-1) approaches, but does not reach, the diffusion limit. This follows from the appreciable solvent kinetic deuterium isotope effects on the rate constants, indicating that, independent of the salt concentration, the rate-limiting step of the catalysis is a chemical process rather than a physical one. The reaction also has positive entropy of activation. On the other hand, the rate-limiting step for substrate QR changes with increasing salt concentration from a physical to chemical step, while the negative activation entropy becomes positive. The rate increase with substrate ER is 50-fold with respect to substrate QR in the presence of 0.1 M NaCl and diminishes to 3.5-fold at 2.0 M NaCl concentration, as a consequence of a considerable rate increase at high salt concentration with substrate QR but not with substrate ER. The Km value is much lower for the substrate ER (0.8 microM) than for substrate QR (15 microM), indicating a more effective binding for substrate ER at 0.1 M NaCl. Unexpectedly, the strong binding appears to be achieved by the unionized form of Glu in P2', as follows from the remarkably different pH-rate profiles for substrates QR and ER. The effective binding elicited by the glutamic acid may be utilized in designing inhibitors for therapeutic purposes.
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PMID:Rate-determining steps in HIV-1 protease catalysis. The hydrolysis of the most specific substrate. 894 73

Mutations were introduced into the active site triplet (Asp-Thr-Gly) of one or both subunits of a linked dimer of human immunodeficiency virus type 1 proteinase. Mutation of Thr to Ser in one or both subunits did not alter the activity of the enzyme substantially, whereas its mutation to Asn in one subunit caused a dramatic decrease in catalytic efficiency. Mutation of Gly to Val in one subunit also yielded an enzyme with very low activity. The enzymes containing Thr-->Asn and Gly-->Val mutations in both subunits resulted in inactive enzymes, based on their inability to self-process and on assay with an oligopeptide substrate. The dramatic decrease in enzyme efficiency of the mutants was interpreted using molecular models of the enzymes.
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PMID:Activity of linked HIV-1 proteinase dimers containing mutations in the active site region. 896 52

The integration of a DNA copy of the retroviral RNA genome into the host cell genome is essential for viral replication. The virion-associated integrase protein, encoded by the 3' end of the viral pol gene, is required for integration. Stable virus-producing T-cell lines were established for replication-defective human immunodeficiency virus type 1 carrying single amino acid substitutions at conserved residues in the catalytic domain of integrase. Phenotypically reverted virus was detected 12 weeks after transfection with the integrase mutant carrying the P-109-->S mutation (P109S). Unlike the defective P109S virus, the revertant virus (designated P109SR) grew in CD4+ SupT1 cells. In addition to the Ser substitution at Pro-109, P109SR had a second substitution of Ala for Thr at position 125 in integrase. Site-directed mutagenesis was used to show that the P109S T125A genotype was responsible for the P109SR replication phenotype. The T125A substitution also rescued the in vitro enzyme activities of recombinant P109S integrase protein. P109S integrase did not display detectable 3' processing or DNA strand transfer activity, although 5 to 10% of wild-type disintegration activity was detected. P109S T125A integrase displayed nearly wild-type levels of 3' processing, DNA strand transfer, and disintegration activities, confirming that T125A is a second-site intragenic suppressor of P109S. P109S integrase ran as a large aggregate on a size exclusion column, whereas wild-type integrase ran as a monomer and P109S T125A integrase ran as a mixed population. Pro-109 and Thr-125 are not immediately adjacent in the crystal structure of the integrase catalytic domain. We suggest that the T125A substitution restores integrase function by stabilizing a structural alteration(s) induced by the P109S mutation.
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PMID:Reversion of a human immunodeficiency virus type 1 integrase mutant at a second site restores enzyme function and virus infectivity. 897 Sep 47


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