| 18093978 |
Nuclear tumor necrosis factor receptor-associated factor 6 in lymphoid cells negatively regulates c-Myb-mediated transactivation through small ubiquitin-related modifier-1 modification |
10.1074/jbc.M706307200. |
J Biol Chem |
Nuclear tumor necrosis factor receptor-associated factor 6 in lymphoid cells negatively regulates c-Myb-mediated transactivation through small ubiquitin-related modifier-1 modification
Abstract
- Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an adaptor/scaffold protein that mediates several important signaling pathways, including the tumor necrosis factor-R:NF-kappaB pathway, involved in immune surveillance, inflammation, etc. Because most studies of TRAF6 function have focused primarily on its role as an adaptor molecule in signaling pathways in the cytoplasm, the potential functions of TRAF6 in other cellular compartments has not been previously investigated. Here, we demonstrate that TRAF6 resides not only in the cellular cytoplasm but is also found in the nuclei of both normal and malignant B lymphocytes. TRAF6 does not possess a nuclear localization signal but enters the nucleus through the nuclear pore complex containing RanGap1. Chromatin immunoprecipitation cloning experiments demonstrated that nuclear TRAF6 associates with c-Myb within the 5'-end of the c-Myb promoter. Further analysis showed that nuclear TRAF6 is modified by small ubiquitin-related modifier-1, interacts with histone deacetylase 1, and represses c-Myb-mediated transactivation. Thus, TRAF6 negatively regulates c-Myb through a novel repressor function in the nuclei of both normal and malignant B-lymphocytes that could represent a novel control mechanism that maintains cell homeostasis and immune surveillance.
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| 18164101 |
Cyclo-glycyl-glutamine inhibits ethanol intake in P and Sprague-Dawley rats |
10.1016/j.peptides.2007.11.009. |
Peptides |
Cyclo-glycyl-glutamine inhibits ethanol intake in P and Sprague-Dawley rats
Abstract
- Peptide inhibitors of ethanol consumption have shown promise. The purpose of this study was to test the cyclized form of the opioid-derived dipeptide, glycyl-L-glutamine to reduce ethanol consumption after either peripheral injections or site-specific injections into the nucleus accumbens (NAC) of high drinking and low drinking rats. Following I.P. cyclo-glycyl-glutamine (c-GQ), the data show a mean decrease in ethanol intake of 34.4% in P rats, and 39.4% in Sprague-Dawley rats at doses between 5 and 25mg/kg. The data show that peripherally administered c-GQ is effective in reducing ethanol consumption in both high (P) and low (SD) drinking strains of rats and suggests a therapeutic potential.
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| 18191970 |
The alpine violet, Viola biflora, is a rich source of cyclotides with potent cytotoxicity |
10.1016/j.phytochem.2007.10.023. |
Phytochemistry |
The alpine violet, Viola biflora, is a rich source of cyclotides with potent cytotoxicity
Abstract
- The cyclotides are currently the largest known family of head-to-tail cyclic proteins. The complex structure of these small plant proteins, which consist of approximately 30 amino acid residues, contains both a circular peptide backbone and a cystine knot, the combination of which produces the cyclic cystine knot motif. To date, cyclotides have been found in plants from the Rubiaceae, Violaceace and Cucurbitaceae families, and are believed to be part of the host defence system. In addition to their insecticidal effect, cyclotides have also been shown to be cytotoxic, anti-HIV, antimicrobial and haemolytic agents. In this study, we show that the alpine violet Viola biflora (Violaceae) is a rich source of cyclotides. The sequences of 11 cyclotides, vibi A-K, were determined by isolation and MS/MS sequencing of proteins and screening of a cDNA library of V. biflora in parallel. For the cDNA screening, a degenerate primer against a conserved (AAFALPA) motif in the cyclotide precursor ER signal sequence yielded a series of predicted cyclotide sequences that were correlated to those of the isolated proteins. There was an apparent discrepancy between the results of the two strategies as only one of the isolated proteins could be identified as a cDNA clone. Finally, to correlate amino acid sequence to cytotoxic potency, vibi D, E, G and H were analysed using a fluorometric microculture cytotoxicity assay using a lymphoma cell line. The IC(50)-values of the bracelet cyclotides vibi E, G and H ranged between 0.96 and 5.0 microM while the Möbius cyclotide vibi D was not cytotoxic at 30 microM.
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| 18197605 |
Stylopeptide 2, a proline-rich cyclodecapeptide from the sponge Stylotella sp |
10.1021/np0704856. |
J Nat Prod |
Stylopeptide 2, a proline-rich cyclodecapeptide from the sponge Stylotella sp
Abstract
- A new proline-rich cyclodecapeptide, designated stylopeptide 2, has been isolated from a cytotoxic extract of the Papua New Guinea marine sponge Stylotella sp. and found to correspond to structure 1. The structural assignment was based on HRMS collision-induced dissociation tandem mass spectrometry (CID MS/MS), NMR spectroscopic data, and amino acid analysis, which led to assignment of the absolute configuration.
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| 18207736 |
Novel echinocandin antifungals. Part 1: novel side-chain analogs of the natural product FR901379 |
10.1016/j.bmcl.2007.12.062. |
Bioorg Med Chem Lett |
Novel echinocandin antifungals. Part 1: novel side-chain analogs of the natural product FR901379
Abstract
- A series of novel acylated analogs of the novel water-soluble echinocandin FR901379 have been prepared and evaluated for antifungal and hemolytic activity. A relationship between antifungal activity and lipophilicity of the acyl side chain, expressed as ClogP was demonstrated, and an analog (3c) with 5.5- to 8-fold superior in vivo activity relative to the previously disclosed 4-(n-octyloxy)benzoyl side chain analog, FR131535 obtained.
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| 18212045 |
CtBP is an essential corepressor for BCL6 autoregulation |
10.1128/MCB.01400-07. |
Mol Cell Biol |
CtBP is an essential corepressor for BCL6 autoregulation
Abstract
- The transcription repressor BCL6 plays an essential role in the formation and function of germinal centers (GCs). While normal B cells promptly shut off BCL6 when they exit the GC, many GC-derived B-cell lymphomas sustain BCL6 expression through chromosomal translocations and activating mutations. We have previously shown that a common effect of lymphoma-associated BCL6 gene alterations is to bypass a negative autoregulatory loop that controls its transcription. In this study, we report that BCL6 autoregulation is independent of several known corepressor complexes including silencing mediator for retinoid and thyroid hormone receptors, nuclear receptor coreceptor, BCL6 corepressor, and MTA3/NuRD. Furthermore, we show that BCL6 can interact with the CtBP (C-terminal binding protein) corepressor both in vitro and in vivo and that CtBP is recruited by BCL6 to its 5' regulatory region. In lymphoma cell lines carrying BCL6 translocations, small interfering RNA-mediated CtBP knock-down selectively relieved the previously silenced wild-type BCL6 allele but not the translocated alleles, which are driven by heterologous promoters. These results demonstrate that CtBP is a novel BCL6 corepressor and suggest that a unique corepressor requirement for BCL6 autoregulation may allow GC B cells to differentially control the expression of BCL6 and other BCL6 target genes in response to environmental stimuli during the GC stage of B cell development.
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| 18212107 |
Drosomycin-like defensin, a human homologue of Drosophila melanogaster drosomycin with antifungal activity |
10.1128/AAC.00155-07. |
Antimicrob Agents Chemother |
Drosomycin-like defensin, a human homologue of Drosophila melanogaster drosomycin with antifungal activity
Abstract
- Innate antifungal defense in Drosophila melanogaster relies on the activation of the Toll molecule and the release of drosomycin, a defensin-like molecule with antifungal properties. Ten human homologues of Toll have been described, with central roles in activation of the innate host defense. In the present study, we report a putative human homologue of the Drosophila-derived drosomycin, designated drosomycin-like defensin (DLD). Synthetic DLD displays a broad spectrum of activity against Aspergillus spp. and other clinically relevant filamentous fungi. These effects are specific for filamentous fungi; no activity has been found against yeasts or gram-positive or gram-negative bacteria. Synthetic DLD also displays immunomodulatory effects on Aspergillus-stimulated cytokine production. In addition, we show the expression of DLD mRNA in several human tissues, particularly in the skin, consistent with its putative role as a defensin against invading microorganisms. This is the first indication of an endogenous human peptide with specific antifungal activity, which is probably central in the defense against infections with molds.
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| 18215770 |
Determining the structure and mode of action of microbisporicin, a potent lantibiotic active against multiresistant pathogens |
10.1016/j.chembiol.2007.11.009. |
Chem Biol |
Determining the structure and mode of action of microbisporicin, a potent lantibiotic active against multiresistant pathogens
Abstract
- Antibiotics blocking bacterial cell wall assembly (beta-lactams and glycopeptides) are facing a challenge from the progressive spread of resistant pathogens. Lantibiotics are promising candidates to alleviate this problem. Microbisporicin, the most potent antibacterial among known comparable lantibiotics, was discovered during a screening applied to uncommon actinomycetes. It is produced by Microbispora sp. as two similarly active and structurally related polypeptides (A1, 2246-Da and A2, 2230-Da) of 24 amino acids linked by 5 intramolecular thioether bridges. Microbisporicin contains two posttranslational modifications that have never been reported previously in lantibiotics: 5-chloro-trypthopan and mono- (in A2) or bis-hydroxylated (in A1) proline. Consistent with screening criteria, microbisporicin selectively blocks peptidoglycan biosynthesis, causing cytoplasmic UDP-linked precursor accumulation. Considering its spectrum of activity and its efficacy in vivo, microbisporicin represents a promising antibiotic to treat emerging infections.
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| 18220336 |
Combining protein-based IMAC, peptide-based IMAC, and MudPIT for efficient phosphoproteomic analysis |
10.1021/pr0705441 |
Journal of proteome research |
Combining protein-based IMAC, peptide-based IMAC, and MudPIT for efficient phosphoproteomic analysis
Abstract
- Immobilized metal affinity chromatography (IMAC) is a common strategy used for the enrichment of phosphopeptides from digested protein mixtures. However, this strategy by itself is inefficient when analyzing complex protein mixtures. Here, we assess the effectiveness of using protein-based IMAC as a pre-enrichment step prior to peptide-based IMAC. Ultimately, we couple the two IMAC-based enrichments and MudPIT in a quantitative phosphoproteomic analysis of the epidermal growth factor pathway in mammalian cells identifying 4470 unique phosphopeptides containing 4729 phosphorylation sites.
|
| 18227510 |
The T790M mutation in EGFR kinase causes drug resistance by increasing the affinity for ATP |
10.1073/pnas.0709662105. |
Proc Natl Acad Sci U S A |
The T790M mutation in EGFR kinase causes drug resistance by increasing the affinity for ATP
Abstract
- Lung cancers caused by activating mutations in the epidermal growth factor receptor (EGFR) are initially responsive to small molecule tyrosine kinase inhibitors (TKIs), but the efficacy of these agents is often limited because of the emergence of drug resistance conferred by a second mutation, T790M. Threonine 790 is the "gatekeeper" residue, an important determinant of inhibitor specificity in the ATP binding pocket. The T790M mutation has been thought to cause resistance by sterically blocking binding of TKIs such as gefitinib and erlotinib, but this explanation is difficult to reconcile with the fact that it remains sensitive to structurally similar irreversible inhibitors. Here, we show by using a direct binding assay that T790M mutants retain low-nanomolar affinity for gefitinib. Furthermore, we show that the T790M mutation activates WT EGFR and that introduction of the T790M mutation increases the ATP affinity of the oncogenic L858R mutant by more than an order of magnitude. The increased ATP affinity is the primary mechanism by which the T790M mutation confers drug resistance. Crystallographic analysis of the T790M mutant shows how it can adapt to accommodate tight binding of diverse inhibitors, including the irreversible inhibitor HKI-272, and also suggests a structural mechanism for catalytic activation. We conclude that the T790M mutation is a "generic" resistance mutation that will reduce the potency of any ATP-competitive kinase inhibitor and that irreversible inhibitors overcome this resistance simply through covalent binding, not as a result of an alternative binding mode.
|
| 18258598 |
Alanine scanning mutagenesis of the prototypic cyclotide reveals a cluster of residues essential for bioactivity |
10.1074/jbc.M709303200. |
J Biol Chem |
Alanine scanning mutagenesis of the prototypic cyclotide reveals a cluster of residues essential for bioactivity
Abstract
- The cyclotides are stable plant-derived mini-proteins with a topologically circular peptide backbone and a knotted arrangement of three disulfide bonds that form a cyclic cystine knot structural framework. They display a wide range of pharmaceutically important bioactivities, but their natural function is in plant defense as insecticidal agents. To determine the influence of individual residues on structure and activity in the prototypic cyclotide kalata B1, all 23 non-cysteine residues were successively replaced with alanine. The structure was generally tolerant of modification, indicating that the framework is a viable candidate for the stabilization of bioactive peptide epitopes. Remarkably, insecticidal and hemolytic activities were both dependent on a common, well defined cluster of hydrophilic residues on one face of the cyclotide. Interestingly, this cluster is separate from the membrane binding face of the cyclotides. Overall, the mutagenesis data provide an important insight into cyclotide biological activity and suggest that specific self-association, in combination with membrane binding mediates cyclotide bioactivities.
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| 18265435 |
Isolation and characterization of a C12-lipopeptide produced by Bacillus subtilis HSO 121 |
10.1002/psc.1017. |
J Pept Sci |
Isolation and characterization of a C12-lipopeptide produced by Bacillus subtilis HSO 121
Abstract
- A new lipopeptide with C12 fatty acid has been isolated from the cell broth of Bacillus subtilis HSO121 by chromatographic methods, which is believed to be the homologue of lipopeptides. The fatty acid portion was methylated and analyzed by GC/MS, ESI Q-TOF MS and 1H-NMR. The peptide portion, of which the amino acid composition was obtained by HPLC combined with a phenyl isothiocyanate (PITC) derivatization methods, was analyzed by ESI Q-TOF MS. Comparing the obtained results with surfactin C13 showed that the new lipopeptide has a peptide moiety similar to that of surfactin and the difference exists in the fatty acid portion, which is an iso-C12 beta-hydroxy fatty acid. The critical micelle concentration (CMC) of this new homologue is estimated to be 6.27 x 10(-5) mol/l in 10 mmol/l phosphate buffer solution (PBS, pH 8.0) at 30 degrees C, and the surface tension at CMC (gamma CMC) achieved is as little as 27.71 mN/m. The hemolytic activities of the C12-lipopeptide on 2% human erythrocytes showed a HC50 of 26.5 micromol/l.
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| 18271554 |
Antifouling activity of a dibrominated cyclopeptide from the marine sponge Geodia barretti |
10.1021/np0705209. |
J Nat Prod |
Antifouling activity of a dibrominated cyclopeptide from the marine sponge Geodia barretti
Abstract
- Many sessile suspension-feeding marine organisms rely on chemical defense to keep their surfaces free from fouling organisms. The brominated cyclopeptides barettin (cyclo[(6-bromo-8-entryptophan)arginine]) ( 1) and 8,9-dihydrobarettin (cyclo[(6-bromotryptophan)arginine]) ( 2) from the cold-water sponge Geodia barretti have previously displayed settlement inhibition of barnacle larvae in a dose-dependent manner. In this paper, we describe a novel dibrominated cyclopeptide, bromobenzisoxazolone barettin (cyclo[(6-bromo-8-(6-bromobenzioxazol-3(1 H)-one)-8-hydroxy)tryptophan)]arginine) ( 3), which we have isolated from G. barretti and which displays settlement inhibition of barnacle larvae ( Balanus improvisus) with an EC 50 value of 15 nM. The chemical structure was determined using MS and 2D-NMR.
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| 18278056 |
Structural and biochemical characterization of the KRLB region in insulin receptor substrate-2 |
10.1038/nsmb.1388. |
Nat Struct Mol Biol |
Structural and biochemical characterization of the KRLB region in insulin receptor substrate-2
Abstract
- Insulin receptor substrates 1 and 2 (IRS1 and -2) are crucial adaptor proteins in mediating the metabolic and mitogenic effects of insulin and insulin-like growth factor 1. These proteins consist of a pleckstrin homology domain, a phosphotyrosine binding domain and a C-terminal region containing numerous sites of tyrosine, serine and threonine phosphorylation. Previous yeast two-hybrid studies identified a region unique to IRS2, termed the kinase regulatory-loop binding (KRLB) region, which interacts with the tyrosine kinase domain of the insulin receptor. Here we present the crystal structure of the insulin receptor kinase in complex with a 15-residue peptide from the KRLB region. In the structure, this segment of IRS2 is bound in the kinase active site with Tyr628 positioned for phosphorylation. Although Tyr628 was phosphorylated by the insulin receptor, its catalytic turnover was poor, resulting in kinase inhibition. Our studies indicate that the KRLB region functions to limit tyrosine phosphorylation of IRS2.
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| 18279990 |
Diversity in Beauvericin and Enniatins H, I, and MK1688 by Fusarium oxysporum isolated from potato |
10.1016/j.ijfoodmicro.2008.01.009. |
Int J Food Microbiol |
Diversity in Beauvericin and Enniatins H, I, and MK1688 by Fusarium oxysporum isolated from potato
Abstract
- Beauvericins and enniatins are cyclohexadepsipeptide mycotoxins that exhibit phytotoxicity and insecticidal activities. In the present study, the production of beauvericin and newly found enniatins (H, I, and MK1688) was characterized in 28 Fusarium strains isolated from potato samples in Korea. The predominant Fusarium species in potato was F. oxysporum (53.6%). Fifteen strains of F. oxysporum and two strains of other Fusarium species produced beauvericin (at concentrations from 3.1 to 743.2 microg/g) in culture on rice. Enniatins H and I were produced by 3 and 11 strains at concentrations from 33.1 to 781.3 microg/g and from 6.5 to 730.3 microg/g, respectively. Five isolates produced enniatin MK1688 at concentrations from 4.6 to 432.6 microg/g. In particular, one isolate (No. 1501) identified as F. oxysporum and two other Fusarium strains (Nos. 804 and 910) produced all of the tested toxins. These results indicate that enniatins H, I, and MK1688 and beauvericin are produced by Fusarium isolates occurring on potato. We do not know if the toxins can accumulate in the environment since it was not demonstrated.
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