emerimicins and peptaibolin

Peptaibols are membrane-active polypeptides isolated from fungal sources. They are characterized by the presence of an unusual amino acid, alpha-aminoisobutyric acid, and a C-terminal hydroxylated amino acid. Peptaibols exhibit antibiotic activity against bacteria and fungi. Their amphipathic nature allows them to self-associate into oligomeric ion-channel assemblies which span the width of lipid bilayer membranes. Over 200 peptaibol sequences have been reported to date, which are compiled in the Peptaibol Database at http://www.cryst.bbk.ac.uk/peptaibol. Alignments of these sequences have been carried out in order to define a series of related subfamilies (SFs) with common sequence features thought to be important for channel formation. Crystal structures determined for a number of peptaibols from the various SFs provide the bases both for modelling of the channel structures and for modelling structures of other members of the same SFs.

Topics: Alamethicin; Amino Acid Sequence; Anti-Bacterial Agents; Conserved Sequence; Crystallography, X-Ray; Ion Channels; Models, Biological; Peptaibols; Peptides; Sequence Alignment

Fungal species of genus

Topics: Antifungal Agents; Antineoplastic Agents; Ascomycota; Botrytis; Esters; Glutamic Acid; Humans; Hypocreales; Neoplasms; Peptaibols; Phytophthora infestans; Tumor Cells, Cultured

In this study, we investigate the effect of nine noncanonical α,α-dialkyl glycines on the structure, dynamics, and membrane permeation properties of a small peptaibol, peptaibolin. The noncanonical amino acids under study are Aib (α-amino isobutyric acid), Deg (α,α-diethyl glycine), Dpg (α,α-dipropyl glycine), Dibg (α,α-di-isobutyl glycine), Dhg (α,α-dihexyl glycine), DΦg (α,α-diphenyl glycine), Db(z)g (α,α-dibenzyl glycine), Ac6c (α,α-cyclohexyl glycine), and Dmg (α,α-dihydroxymethyl glycine). It is hypothesized that these amino acids are able to induce well-defined secondary structures in peptidomimetics. To investigate this hypothesis, we designed new peptaibolin peptidomimetics by replacing the native Aib positions with a new α,α-dialkyl glycine. We show that Dhg and Ac6c noncanonical amino acids are able to induce α-helix secondary structures of peptaibolin in water, which are not present in the native structure. We also demonstrate that the α,α-dialkyl glycines increase the membrane permeability of peptaibolin in 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) membranes. However, there is no apparent correlation between increased helicity and membrane permeability. In summary, we show that some α,α-dialkyl glycines under study induce the formation of α-helix secondary structures in peptaibolin and promote spontaneous membrane permeation. Our findings increase the knowledge of the membrane permeability and folding of peptides incorporating α,α-dialkyl glycines.

Topics: Cell Membrane Permeability; Glycine; Molecular Dynamics Simulation; Peptaibols; Phosphatidylcholines; Protein Structure, Secondary; Water

Extraction followed by reverse phase liquid chromatography (LC)/electrospray ionization-ion trap-mass spectrometry (ESI-IT-MS) analysis has been successfully developed for the determination of peptaibols, fungal toxic metabolites, in marine sediments. Spiking experiments showed that the mean recovery of target compounds exceeded 85% at a spiking level of 10 ng/g of sediment (wet weight). Detection and quantification limits were 250 and 830 pg/g of sediment, respectively. The method developed constituted the first sensitive assay for quantification of peptaibol trace amounts in a natural environment. A concentration of 5 ng/g in sediment samples collected from Fier d'Ars was found.

Topics: Alamethicin; Calibration; Chromatography, Liquid; Complex Mixtures; Environment; Geologic Sediments; Peptaibols; Peptides; Reproducibility of Results; Solvents; Spectrometry, Mass, Electrospray Ionization

The fragmentations of [M+H]+ and [M+Na]+ adducts of neutral peptides with blocked N- and C-termini have been investigated using electrospray ion trap mass spectrometry. The N-termini of these synthetically designed peptides are blocked with a tertiarybutyloxycarbonyl (Boc) group, and the C-termini are esterified. These peptides do not possess side chains that are capable of complexation and hence the backbone amide units are the sole sites of protonation and metallation. The cleavage patterns of the protonated peptides are strikingly different from those of sodium ion adducts. While the loss of the N-terminal blocking group occurs quite readily in the case of MS/MS of [M+Na]+, the cleavage of the C-terminal methoxy group seems to be a facile process in the case of MS/MS of [M+H]+ * Fragmentation of the protonated adducts yields only bn ions, while yn and a(n) ions are predominantly formed from the fragmentation of sodium ion adducts. The a(n) ions arising from the fragmentation of [M+Na](+) lack the N-terminal Boc group (and are here termed a(n)* ions). MS/MS of [M+Na]+ species also yields b(n) ions of substantially lower intensities that lack the N-terminal Boc group (b(n)*). A similar distinction between the fragmentation patterns of proton and sodium ion adducts is observed in the case of peptides possessing an N-terminal acetyl group. An example of the fragmentation of the H+ and Na+ adducts of a naturally occurring peptaibol from a Trichoderma species confirms that fragmentation of these two ionized species yields complementary information, useful in sequencing natural peptides. Inspection of the isotopic pattern of b(n) ions derived from [M+H]+ adducts of peptaibols provided insights into the sequences of microheterogeneous samples. This study reveals that the combined use of protonated and sodium ion adducts should prove useful in de novo sequencing of peptides, particularly of naturally occurring neutral peptides with modified N- and C-termini, for example, peptaibols.

Topics: Amino Acid Sequence; Anti-Bacterial Agents; Models, Biological; Molecular Sequence Data; Peptaibols; Peptide Fragments; Peptides; Protons; Recombinant Proteins; Sodium; Spectrometry, Mass, Electrospray Ionization

Trichoderma virens, an imperfect fungus, is used as a biocontrol agent to suppress plant disease caused by soilborne fungal pathogens. Antimicrobial peptides it produces include peptaibols of 11, 14, and 18 amino acids in length. These peptaibols were previously reported to be synthesized by a non-ribosomal peptide synthetase (NRPS) encoded by the Tex1 gene in strain Tv29-8. The present study examined the Tex1 homolog in a commercially relevant T. virens strain, G20. Although the gene in G20 was 99% identical in DNA sequence to Tex1 in the 15.8 kb compared, gene disruption results indicate that it is only responsible for the production of an 18-mer peptaibol, and not 11-mer and 14-mer peptaibols. Additional NRPS adenylate domains were identified in T. virens and one was found to be part of a 5-module NRPS gene. Although the multimodule gene is not needed for peptaibol synthesis, sequence comparisons suggest that two of the individual adenylate domain clones might be part of a separate peptaibol synthesis NRPS gene. The results indicate a significant diversity of NRPS genes in T. virens that is unexpected from the literature.

Topics: Molecular Sequence Data; Peptaibols; Peptide Synthases; Peptides; Pest Control, Biological; Phylogeny; Plant Diseases; Trichoderma

The sequence entries in the Peptaibol Database were analysed to provide information on compositional features of this unusual family of peptides. The non-standard amino acid alpha-aminoisobutyric acid represents almost 40% of the residues in all the known sequences. Glutamine is the only significant polar residue in peptaibols, and the position and number of these residues appear to be related to their functional properties as ion channels. Aromatic residues are clustered at the termini, which may contribute to stabilization of the peptide vertically within the bilayer. The peptide chain length is strongly weighted towards the longer members of the family (16-20 residues) and likely to be an important feature in their mode of action as transmembrane permeabilizers. The significant skewing towards even numbers of residues and the bias in pairwise distributions of amino acids have implications for the nature of the in vivo synthesis of these peptides via large non-ribosomal protein complexes.

Topics: Amino Acid Sequence; Aminoisobutyric Acids; Cell Membrane Permeability; Databases, Protein; Glutamine; Information Storage and Retrieval; Internet; Ion Channels; Peptaibols; Peptide Biosynthesis, Nucleic Acid-Independent; Peptide Fragments; Peptides; Protein Conformation; Sequence Analysis, Protein

Using a pore- and channel-forming peptide, TV-XIIa, which is an 11-residual peptaibol isolated from the fungus Trichoderma viride, we developed a vehicle for the cellular delivery of such polar biologically active agents as antisense oligodeoxynucleotides (ODNs). To function as an ODN carrier, basic amino acids, 10-mer of lysine, were conjugated to the C-terminus of TV-XIIa and the designed carrier peptide, Ac-U-N-I-I-U-P-L-L-U-P-I-K-K-K-K-K-K-K-K-K-K-OH (U: alpha-aminoisobutyric acid), was synthesized by the Fmoc-based solid-phase method. The complex between the carrier peptide and ODNs, which was electrostatically formed, was capable of crossing the membranes of NIH3T3 cells and the ODNs were accumulated in the cytoplasm and the nucleus. However, the complex was not taken up by A549 cells. The translocation of the complex occurred at both 4 and 37 degrees C in NIH3T3 cells and did not seem to involve an energy-dependent endocytic process.

Topics: Amino Acid Sequence; Animals; Biological Transport; Cell Membrane; Cell Nucleus; Cytoplasm; Drug Carriers; Fluorescent Dyes; Mice; Microscopy, Fluorescence; NIH 3T3 Cells; Oligodeoxyribonucleotides; Peptaibols; Peptides; Trichoderma

We have synthesized by solution methods and characterized the lipopeptaibol metabolite LP237-F8 extracted from the fungus Tolypocladium geodes and five selected analogues with the Etn-->Aib or Etn-->Nva replacement at position 8 and/or a triple Gln-->Glu(OMe) replacement at positions 5, 6, and 9 (Etn=Calpha-ethylnorvaline, Aib=alpha-aminoisobutyric acid, Nva=norvaline). Conformation analysis, performed by FT-IR absorption, NMR, and CD techniques, strongly supports the view that the six terminally blocked decapeptides are highly helical in solution. Helix topology and amphiphilic character are responsible for their remarkable membrane activity. At position 8 the combination of high hydrophobicity and Calpha tetrasubstitution, as in the Etn-containing LP237-F8 metabolite, has a positive effect on membrane interaction.

Topics: Amino Acid Sequence; Anti-Bacterial Agents; Cell Membrane Permeability; Circular Dichroism; Fluorescent Dyes; Hydrogen Bonding; Membranes, Artificial; Mitosporic Fungi; Models, Molecular; Nuclear Magnetic Resonance, Biomolecular; Peptaibols; Peptides; Phosphatidylcholines; Phospholipids; Protein Conformation; Spectrometry, Fluorescence; Spectroscopy, Fourier Transform Infrared

By a cell-based screening of an in-house natural product library, trichorzin HA V, belonging to a peptaibol family, was isolated from a strain of fungus Trichoderma as a calcitonin (CT) agonist. Like CT, trichorzin HA V elevated cAMP levels in T47D cells which endogenously express the human CT receptor. It also stimulated cAMP formation in cells expressing recombinant human CT receptor, but not in those that do not express the receptor, suggesting that it selectively interacts with the CT receptor. In contrast to trichorzin HA V, alamethicin, another well-characterized peptaibol, showed no cAMP-elevating activity at all. These results suggest that, although there was little amino acid sequence similarity between trichorzin HA V and CT, the biological activity of trichorzin HA V can mimic that of CT, acting via the CT receptor.

Topics: Animals; Anti-Bacterial Agents; Cell Line; CHO Cells; Cricetinae; Cyclic AMP; Dose-Response Relationship, Drug; Humans; Intercellular Signaling Peptides and Proteins; Intracellular Fluid; Ionophores; Peptaibols; Peptides; Receptors, Calcitonin; Tumor Cells, Cultured

The effect of a transmembrane potential on ion channel formation by zervamicin II (ZER-II) was studied in a vesicular model system. The dissipation of diffusion potential caused by addition of ZER-II to small phosphatidylcholine vesicles was monitored using fluorescent (Safranine T) and optical (Oxonol YI) probes. Cis-positive potentials facilitated channel formation, while at cis-negative potentials, ion fluxes were inhibited. A potential-independent behavior of ZER-II was observed at high peptide concentrations, most likely due to its membrane modifying property.

Topics: Alamethicin; Amino Acid Sequence; Anti-Bacterial Agents; Electric Conductivity; Ion Channels; Membrane Potentials; Molecular Sequence Data; Peptaibols; Peptides; Phospholipids; Valinomycin

Topics: Anti-Bacterial Agents; Molecular Structure; Peptaibols; Peptides