The peculiar N- and C-termini of trichogin GA IV are needed for membrane interaction and human cell death induction at doses lacking antibiotic activity

Peptaibiotics, non-ribosomally synthetized peptides from various ascomycetes, are uniquely characterized by di-alkylated alpha-amino acids, a rigid helical conformation, and membrane permeation properties. Although generally considered as antimicrobial peptides, peptaibiotics may display other toxicological properties, and their function is in many cases unknown. With the goal to define the biological activity and selectivity of the peptaibiotic trichogin GA IV from the human opportunist Trichoderma longibrachiatum we analyzed its membrane interaction, cytotoxic activity and antibacterial effect. Trichogin GA IV effectively killed several types of healthy and neoplastic human cells at doses (EC 50% = 4-6 μM) lacking antibiotic effects on both Gram- and Gram+ bacteria (MIC > 64 μM). The peptaibiotic distinctive C-terminal primary alcohol was found to cooperate with the N-terminal n-octanoyl group to permeate the membrane phospholipid bilayer and to mediate effective binding and active endocytosis of trichogin GA IV in eukaryotic cells, two steps essential for cell death induction. Replacement of one Gly with Lys plus the simultaneous esterification of the C-terminus, strongly increased trichogin GA IV anti-Gram+ activity (MIC 1-4 μM), but further mitigated its cytotoxicity on human cells.