Structure of actinotetraose hexatiglate, a unique glucotetraose from an actinomycete bacterium.
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An Actinomycete strain A499 belonging to the genera Amycolatopsis or Amycolata isolated from a Western Australian soil sample produced the cyclic decapeptide antibiotic quinaldopeptin (1), together with the actinotetraose hexatiglate (2), the hexa-ester of a novel non-reducing glucotetraose. (+info)
SW-163C and E, novel antitumor depsipeptides produced by Streptomyces sp. II. Structure elucidation.
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SW-163C and E are novel antitumor antibiotics, which belong to quinomycin family, isolated from the culture broth of Streptomyces sp. SNA15896. These compounds were determined to be cyclic depsipeptides having 3-hydroxyquinaldic acid as a chromophore and a sulfur-containing intramolecular cross linkage through various spectroscopic analyses. (+info)
The 2-amino group of guanine is absolutely required for specific binding of the anti-cancer antibiotic echinomycin to DNA.
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The 2-amino group of guanine is believed to be a critical determinant of potential DNA binding sites for echinomycin and related quinoxaline antibiotics. In order to probe its importance directly we have studied the interaction between echinomycin and DNA species in which guanine N(2) is deleted by virtue of substitution of inosine for guanosine residues. The polymerase chain reaction was used to prepare inosine-substituted DNA. Binding of echinomycin, assessed by DNAse I footprinting, was practically abolished by incorporation of inosine into one or both strands of DNA. We conclude that both the purines in the preferred CpG binding site need to bear a 2-amino group to interact with echinomycin. (+info)
Energetics of echinomycin binding to DNA.
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Differential scanning calorimetry and UV thermal denaturation have been used to determine a complete thermodynamic profile for the bis-intercalative interaction of the peptide antibiotic echinomycin with DNA. The new calorimetric data are consistent with all previously published binding data, and afford the most rigorous and direct determination of the binding enthalpy possible. For the association of echinomycin with DNA, we found DeltaG degrees = -7.6 kcal mol(-1), DeltaH = +3.8 kcal mol(-1) and DeltaS = +38.9 cal mol(-1) K(-1) at 20 degrees C. The binding reaction is clearly entropically driven, a hallmark of a process that is predominantly stabilized by hydrophobic interactions, though a deeper analysis of the free energy contributions suggests that direct molecular recognition between echinomycin and DNA, mediated by hydrogen bonding and van der Waals contacts, also plays an important role in stabilizing the complex. (+info)
Echinomycin inhibits chromosomal DNA replication and embryonic development in vertebrates.
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Echinomycin, a member of the quinoxaline family of antibiotics, is known to be a strong inhibitor of RNA synthesis which has been attributed to its ability to bind to double-helical DNA. Here we study the effect of echinomycin upon DNA replication using egg extracts and embryos from Xenopus laevis as well as cultured human cells. Evidence is presented that echinomycin interferes with chromatin decondensation, nuclear assembly and DNA replication. In the absence of transcription and translation, the drug specifically blocks DNA replication in both Xenopus sperm chromatin and HeLa cell nuclei in vitro. By contrast, replication of single-stranded DNA is not inhibited indicating that echinomycin acts by interacting with the DNA and not the replication elongation proteins of chromatin. The addition of the antibiotic to HeLa cells and X.laevis embryos results in anaphase bridges and cell death. Importantly, in X.laevis embryos injected with echinomycin at the two-cell stage the drug specifically inhibits the cell cycle prior to the onset of transcription, suggesting that quinoxaline antibiotics could exert anti- proliferative effects by inhibition of chromosomal DNA replication. (+info)
Respiratory burst induced by phorbol ester in the presence of tautomycin, a novel inhibitor of protein phosphatases.
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Phorbol dibutyrate induced a nitroblue tetrazolium-reducing reaction in differentiated HL-60 cells, which was inhibited by protein kinase inhibitors such as staurosporine and H-7. ID50 of staurosporine and H-7 were 1.4 ng/ml and 0.19 mM, respectively. When tautomycin, an inhibitor of protein phosphatases, was added with the kinase inhibitors, the nitroblue tetrazolium-reducing reaction again appeared. ID50 of staurosporine was 510 ng/ml in the presence of tautomycin. Tautomycin itself weakly induced the reaction, which was inhibited by kinase inhibitors. Such a competitive effect between tautomycin and staurosporine was not observed in a cell-free system of protein kinase C. Okadaic acid had the same effect as tautomycin. The similar results were obtained when respiratory burst was quantitated by measuring H2O2 produced by canine peripheral neutrophils. The mechanism of competitive effect of tautomycin and staurosporine on respiratory burst is discussed. (+info)
Functional cross-talk between fatty acid synthesis and nonribosomal peptide synthesis in quinoxaline antibiotic-producing streptomycetes.
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Quinoxaline antibiotics are chromopeptide lactones embracing the two families of triostins and quinomycins, each having characteristic sulfur-containing cross-bridges. Interest in these compounds stems from their antineoplastic activities and their specific binding to DNA via bifunctional intercalation of the twin chromophores represented by quinoxaline-2-carboxylic acid (QA). Enzymatic analysis of triostin A-producing Streptomyces triostinicus and quinomycin A-producing Streptomyces echinatus revealed four nonribosomal peptide synthetase modules for the assembly of the quinoxalinoyl tetrapeptide backbone of the quinoxaline antibiotics. The modules were contained in three protein fractions, referred to as triostin synthetases (TrsII, III, and IV). TrsII is a 245-kDa bimodular nonribosomal peptide synthetase activating as thioesters for both serine and alanine, the first two amino acids of the quinoxalinoyl tetrapeptide chain. TrsIII, represented by a protein of 250 kDa, activates cysteine as a thioester. TrsIV, an unstable protein of apparent Mr about 280,000, was identified by its ability to activate and N-methylate valine, the last amino acid. QA, the chromophore, was shown to be recruited by a free-standing adenylation domain, TrsI, in conjunction with a QA-binding protein, AcpPSE. Cloning of the gene for the QA-binding protein revealed that it is the fatty acyl carrier protein, AcpPSE, of the fatty acid synthase of S. echinatus and S. triostinicus. Analysis of the acylation reaction of AcpPSE by TrsI along with other A-domains and the aroyl carrier protein AcmACP from actinomycin biosynthesis revealed a specific requirement for AcpPSE in the activation and also in the condensation of QA with serine in the initiation step of QA tetrapeptide assembly on TrsII. These data show for the first time a functional interaction between nonribosomal peptide synthesis and fatty acid synthesis. (+info)
Proton NMR study of the [d(ACGTATACGT)]2-2echinomycin complex: conformational changes between echinomycin binding sites.
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The interactions of echinomycin and the DNA decamer [d(ACGTATACGT)]2 were studied by proton NMR. Echinomycin binds cooperatively as a bisintercalator at the CpG steps. The terminal A.T base pairs are Hoogsteen base paired, but none of the four central A.T base pairs are Hoogsteen base paired. However, binding of the drug induces unwinding of the DNA which is propagated to the central ApT step. All four central A.T base pairs are destabilized relative to those in the free DNA. Furthermore, based on these and other results from our laboratory, we conclude that the formation of stable Hoogsteen base pairs may not be the relevant structural change in vivo. The structural changes propagated between adjacent ACGT binding sites are the unwinding of the duplex and destabilization of the base pairing between binding sites. (+info)