Sequences of stilboflavin C: towards the peptaibiome of the filamentous fungus Stilbella (= Trichoderma) flavipes

Filamentous fungi of the genus Stilbella are recognized as an abundant source of naturally occurring α‐aminoisobutyric acid‐containing peptides. The culture broth of Stilbella (Trichoderma) flavipes CBS 146.81 yielded a mixture of peptides named stilboflavins (SF), and these were isolated and separated by preparative TLC into groups named SF‐A, SF‐B, and SF‐C. Although all three of these groups resolved as single spots on thin‐layer chromatograms, HPLC analysis revealed that each of the groups represents very microheterogeneous mixtures of closely related peptides. Here, we report on the sequence analysis of SF‐C peptides, formerly isolated by preparative TLC. HPLC coupled to QqTOF‐ESI‐HRMS provided the sequences of 10 16‐residue peptides and five 19‐residue peptides, all of which were N‐terminally acetylated. In contrast to the previously described SF‐A and SF‐B peptaibols, SF‐C peptaibols contain Ser‐Alaol or Ser‐Leuol, which are rarely found as C‐termini, and repetitive Leu‐Aib‐Gly sequences, which have not been detected in peptaibols before. Taking the previously determined sequences of SF‐A and SF‐B into account, the entirety of peptides produced by S. flavipes (the ‘peptaibiome’) approaches or exceeds 100 non‐ribosomally biosynthesized peptaibiotics. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd. The novel stilboflavin C peptides, namely ten 16‐residue and five 19‐residue sequences, were isolated from submerged cultures of the fungus Stilbella flavipes CBS 146.81 (Image: the species growing on a fallen tree, white scale bar: 1 mm). These peptides contain Ser‐Alaol or Ser‐Leuol, which are rarely found as C‐termini, as well as repetitive motifs (Leu‐Aib‐Gly)2,3 which have not been detected in peptaibols before.