Trichotoxin A-40, a new membrane-exciting peptide. Part A. Isolation,characterization and conformation

The new polypeptide antibiotic trichotoxin A-40 is isolated by chloroform/methanol extraction from the dry mycelium of Trichoderma viride NRRL 5242. The lipophilic peptide is purified by chromatography on Kieselgel H-60 and reverse-phase chromatography on Lichrosorb RP-8. The new antibiotic differs in amino acid composition and various chemical and physicochemical properties from similar peptides such as trichotoxin A, the suzukacillins or alamethicins. The amino acid composition is (Pro)₁ (Gly)₁ (Ala)₂ (Leu)₂ (Aib)₁₀ (Glx)₂. (Aib, α-aminoisobutyric acid.) The antibiotic has a carboxyl group which can be esterified by diazomethane, which results in slightly enhanced membrane-modifying activities.The peptide exhibits a right-handed α-helical conformation increasing about two-fold from aqueous to lipophilic media as shown by solvent-dependent circular dichroism measurements. Most of the ¹³C-NMR resonances can be assigned unequivocally and amino acids situated in the α-helical part show characteristic shift differences from those in the non-helical regions. No β-phenylalaninol residue could be identified by ¹³C-NMR and ultraviolet spectroscopy, as can be for alamethicins and suzukacillins. A pronounced hemolytic action is found on human erythrocytes, which develops at micromolar concentrations. Trichotoxin A-40 induces a voltage-dependent ionic conductance in bilayer lipid membranes and it can serve as a new pore-forming model system for structure/activity studies in membrane excitation by peptides.