Fungal Metabolites. XX. Effect of Proline Residue on the Structure of Ion-Channel-Forming Peptide, Trichosporin B-VIa

Abstract

The secondary structures of an ion-channel-forming icosapeptaibol, trichosporin B-VIa, and its Aib¹⁴-substituted derivative containing no Pro were investigated on the basis of CD and various NMR experiments in methanol. Trichosporin B-VIa has a fully helical structure with a kink stabilized by a 1←4 hydrogen-bond between the Leu¹² CO and Val¹⁵ NH. The helical structure is composed of 3₁₀-helix in the N-terminal first turn and the C-terminal moiety following Leu¹², and α-helix in the middle region. In contrast, the Aib¹⁴ derivative predominantly has a straight α-helical structure except for a 3₁₀-helix region in the N-terminal first turn.