The Sequences of the Eleven-Residue Peptaibiotics: Suzukacillins-B

The filamentous fungus designated ‘Trichoderma viride’ strain 63 C‐1 simultaneously produces suzukacillins (SZs), two microheterogeneous groups of peptaibols, under submerged culture conditions. Both groups are readily distinguishable by TLC: the major group is designated SZ‐A, whereas the minor group with a higher Rf value is named SZ‐B. The peptide mixture was obtained from a MeOH extract of the mycelium. SZ‐B was separated from SZ‐A by Sephadex LH‐20 column chromatography. Although it provided one single spot on silica‐gel TLC plates, 15 individual peptides could be separated by C8 reversed‐phase (RP) HPLC, and their sequences were determined by HPLC/QqTOF‐ESI‐HRMS. Fourteen peptides exhibit the C‐terminal sequence Pro6‐Lxx‐Lxx‐Aib‐Pro‐Vxxol/Lxxol11, which is common for eleven‐residue peptaibols. The remaining peptide is tentatively assigned as a ten‐residue sequence, in which the C‐terminal 1,2‐amino alcohol is deleted, thus terminating in free proline. Nine of the peptides carry an Ac‐Aib residue at the N‐terminus, very frequently found in eleven‐residue peptaibols. Four peptides comprise the rare Ac‐Ala N‐terminus, and for two peptides, N‐terminal Ac‐D‐Iva residues were identified. One peptide contains a C‐terminal residue of yet undetermined structure. Comparison with previously reported eleven‐residue peptaibol sequences reveals that eight of the peptides represent new sequence analogs.