alamethicin and Hemolysis

Peptaibols and the related peptaibiotics are linear, amphipathic polypeptides. More than 300 of these secondary metabolites have been described to date. These compounds are composed of 5-20 amino acids and are generally produced in microheterogeneous mixtures. Peptaibols and peptaibiotics with unusual amino acid content are the result of non-ribosomal biosynthesis. Large multifunctional enzymes known as peptide synthetases assemble these molecules by the multiple carrier thiotemplate mechanism from a remarkable range of precursors, which can be N-methylated, acylated or reduced. Peptaibols and peptaibiotics show interesting physico-chemical and biological properties including the formation of pores in bilayer lipid membranes, as well as antibacterial, antifungal, occasionally antiviral activities, and may elicit plant resistance. The three-dimensional structure of peptaibols and peptaibiotics is characterized predominantly by one type of the helical motifs alpha-helix, 3(10)-helix and beta-bend ribbon spiral. The aim of this review is to summarize the data available about the biosynthesis, biological activity and conformational properties of peptaibols and peptaibiotics described from Trichoderma species.

Topics: Alamethicin; Amino Acid Sequence; Animals; Anti-Bacterial Agents; Enzyme Activation; Fungal Proteins; Fungi; Gram-Positive Bacteria; Hemolysis; Insecta; Lipopeptides; Microbial Sensitivity Tests; Molecular Sequence Data; Peptaibols; Peptides; Trichoderma; Viruses

Alamethicin is known to lyse different biological cells and to induce voltage dependent ion channels in lipid bilayers. A set of analogs with proline shifted from position 14 in the native peptide towards the N- and C-terminus was used to investigate the role of proline in: (i) alamethicin induced hemolysis of human red blood cells, (ii) stimulation of catecholamine secretion from bovine adrenal chromaffin cells and (iii) induction of metabolic activity in bovine aortic endothelial cells. Half maximal hemolytic activity was found at 30 microM alamethicin concentration, complete lysis occurred at 100 microM. The stimulation of catecholamine secretion in the presence of extracellular Ca2+ was concentration dependent up to 50 microM alamethicin. At this high concentration mild secretion was also found in the absence of Ca2+ indicating cell membrane damage. Alamethicin transiently stimulated the metabolic rate of endothelial cells in a concentration dependent mode up to 20 microM while the inhibition of metabolism at higher concentrations pointed to a toxic effect. The alamethicin analogs were completely inactive in all the biological assays. The effects correlated with a loss of dye release inducing activities on phosphatidylcholine vesicles and reduction of channel forming properties in lipid bilayers and were associated with modifications of membrane affinity rather than conformational changes of the peptides. The results indicate that proline at position 14 of the native peptide is essential for the interaction with different membrane systems.

Topics: Alamethicin; Amino Acid Sequence; Animals; Catecholamines; Cattle; Chromaffin Cells; Endothelium, Vascular; Hemolysis; Humans; Molecular Sequence Data; Proline; Structure-Activity Relationship

Magainin peptides, isolated from Xenopus skin, kill bacteria by permeabilizing their cell membranes whereas they do not lyse erythrocytes. To elucidate the rationale for this membrane selectivity, we compared the effects of the membrane lipid composition and the transmembrane potential on the membrane-lytic power of magainin 2 with that of hemolytic melittin. The activity of magainin to zwitterionic phospholipids constituting the erythrocyte surface was extremely weak compared with that of melittin, and acidic phospholipids are necessary for effective action. The presence of sterols reduced the susceptibility of the membrane to magainin. The generation of an inside-negative transmembrane potential enhanced magainin-induced hemolysis. We can conclude that the absence of any acidic phospholipids on the outer monolayer and the abundant presence of cholesterol, combined with the lack of the transmembrane potential, contribute to the protection of erythrocytes from magainin's attack.

Topics: Alamethicin; Amino Acid Sequence; Animals; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Bacteria; Cell Membrane; DNA-Binding Proteins; Erythrocyte Membrane; Gramicidin; Hemolysis; Humans; In Vitro Techniques; Magainins; Melitten; Membrane Lipids; Membrane Potentials; Molecular Sequence Data; Molecular Structure; Peptides, Cyclic; Phospholipids; Sialic Acids; Sterols; Xenopus Proteins

Paracelsin, a hemolytic and membrane active polypeptide antibiotic of the peptaibol class which is excreted by the mold Trichoderma reesei, was obtained by a simplified and rapid isolation procedure utilizing hydrophobic adsorber resins. Investigation by 13C nuclear magnetic resonance spectroscopy and circular dichroism revealed considerable helical portions in solution, and the very recently accomplished sequence determination of paracelsin allows the discussion of the results with regard to the closely related analogues, alamethicin and suzukacillin. A selective cleavage of the peptide was achieved by careful treatment with various acids, and a buffer of pH 8.25 and of high ionic strength made possible the quantitative determination of the C-terminal phenylalaninol released by means of ion-exchange chromatography. The significance of the production of paracelsin and related mycotoxins of the peptaibol class, exhibiting various kinds of biological activity, is discussed with respect to the extensive effort being made towards biotechnological applications of species, strains and cellulolytically highly active mutants of the fungus Trichoderma.

Topics: Alamethicin; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Chromatography; Chromatography, High Pressure Liquid; Circular Dichroism; Erythrocytes; Hemolysis; Humans; Magnetic Resonance Spectroscopy; Molecular Conformation; Peptides; Phenylalanine; Trichoderma

Topics: Alamethicin; Animals; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Cattle; Cell Membrane; Hemolysis; Humans; Hydrolysis; In Vitro Techniques; Osmolar Concentration; Osmotic Pressure; Peptides; Serum Albumin, Bovine; Thermodynamics; Trichoderma