Unprecedented 17-Residue Peptaibiotics Produced by Marine-Derived Trichoderma atroviride

In the course of investigations on marine-derived toxigenic fungi, five strains of Trichoderma atroviride were studied for their production of peptaibiotics. While these five strains were found to produce classical 19-residue peptaibols, three of them exhibited unusual peptidic sodium-adduct [M+2Na]2+ ion peaks at m/z between 824 and 854. The sequencing of these peptides led to two series of unprecedented 17-residue peptaibiotics based on the model Ac-XXX-Ala-Ala-XXX-XXX-Gln-Aib-Aib-Aib-Ala/Ser-Lxx-Aib-Pro-XXX-Aib-Lxx-[C129]. The C-terminus of these new peptides was common to all of them, and its elemental formula C5H9N2O2 was established by HR-MS. It could correspond to the cyclized form of N-hydroxyornithine which has already been observed at the C-terminus of various peptidic siderophores. The comparison of the sequences of 17- and 19-residue peptides showed similarities for positions 116. This observation seems to indicate a common biosynthesis pathway. Both new 17-residue peptaibiotics and 19-residue peptaibols exhibited weak in vitro cytotoxicities against KB cells.