Sequences of alamethicins F30 and F50 reconsidered and reconciled

From the culture broth of the mould Trichoderma viride, strain NRRL 3199, a microheterogeneous mixture of the membrane active 20-residue peptaibol alamethicin (ALM) could be isolated. ALMs were isolated by XAD-2 column chromatography and separated by silica gel chromatography and trichloromethane/MeOH gradient elution into an acidic and neutral group of Peptides, named ALM F30 and ALM F50, respectively, according to their 100 Rf on TLC. Peptides ALM F50 were separated by semi-preparative and analytical HPLC and subjected to ESI-MS. Ten sequences of ALM F30 and their relative quantities could be determined. The major Peptides ALM F30/3 (46%) and ALM F30/7 (40%), distinguished by Aib/Ala exchange in position 6, correspond to sequences described as ALM I and II occurring in the original alamethicin from Upjohn Company. Analogously, 13 sequences of the neutral peptide mixture named ALM F50 could be determined. The major peptide ALM F50/5 (75%) and the minor peptide ALM F50/7 (10%) are distinguished from ALM F30/3 and ALM F30/7 by having Gln17 in place of Glu17, the latter occurring in the F30 group. Notably. currently commercially available alamethicins (Fluka, Sigma) represent microheterogeneous mixtures of the neutral ALM F50 Peptides with trace amounts of acidic ALM F30 Peptides.