A new family of N-terminally truncated peptaibols from the biocontrol fungus trichoderma harzianum

Peptaibiotics and their subgroup of peptaibols are defined as bioactive microbial peptides containing the characteristic, non-proteinogenic α-aminoisobutyric acid (Aib). They are of permanent interest to both academics and industry owing to their manifold biological activities including unique membrane-modifying properties. Here we report on the sequences of a new class of truncated 16-residue peptaibol-derived peptides isolated from agar plate cultures of the filamentous fungus T. harzianum CBS 226.95. These peptides are the result of an unexpected endoenzymatic cleavage of the N-terminal dipeptide AcAib1-Ser2 from concomitantly produced 18-residue peptaibols, which are structurally related to trichokindins. They display the general sequence AcAib1-Ser2-↓Ala3-(Aaa)4-17-Xol18 (Aaa, amino acid including Aib; Xol, Leuol/Ileol). The biosynthesis of twelve 18-residue trichokindin-type peptaibols and of six truncated 16-residue peptaibiotics with free N-alanyl termini derived thereof (cleavage indicated by arrow), named brevikindins I - VI, provides new insights into the mechanism of non-ribosomal peptaibotic biosynthesis and plant-protective properties of T. harzianum