Unique amalgamation of primary and secondary structural elements transform peptaibols into potent bioactive cell-penetrating peptides

Significance Using a combined approach relying on mass spectrometric analysis and molecular phylogeny, a fungus was identified that produced the gichigamins, which are peptaibols that contain a remarkable combination of structural features. The gichigamins possess a repeating α-residue/α-residue/β-residue motif creating a 3 11 - P -helix secondary structure. These structural elements confer upon the gichigamins the unique ability among peptaibols to enter into cells whereupon they disrupt mitochondrial function. Semisynthetic modifications further enhanced gichigamin mitochondrial depolarization and cytotoxicity, while removing virtually all plasma-membrane pore-forming capabilities. These discoveries open vistas for engineering peptaibols into potent cytotoxins and intracellular delivery tools that are devoid of ion leakage effects.