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

Lin Du, April L. Risinger, Carter A. Mitchell, Jianlan You, Blake W. Stamps, Ning Pan, Jarrod B. King, Jean C. Bopassa, Susan I.V. Judge, Zhibo Yang, Bradley S. Stevenson, Robert H. Cichewicz

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Mass-spectrometry-based metabolomics and molecular phylogeny data were used to identify a metabolically prolific strain of Tolypocladiumthat was obtained from a deep-water Great Lakes sediment sample. An investigation of the isolate's secondary metabolome resulted in the purification of a 22-mer peptaibol, gichigamin A (1). This peptidic natural product exhibited an amino acid sequence including several β-alanines that occurred in a repeating ααβ motif, causing the compound to adopt a unique right-handed 311 helical structure. The unusual secondary structure of 1 was confirmed by spectroscopic approaches including solution NMR, electronic circular dichroism (ECD), and single-crystal X-ray diffraction analyses. Artificial and cell-based membrane permeability assays provided evidence that the unusual combination of structural features in gichigamins conferred on them an ability to penetrate the outer membranes of mammalian cells. Compound 1 exhibited potent in vitro cytotoxicity (GI50 0.55 ± 0.04 μM) and in vivo antitumor effects in a MIA PaCa-2 xenograft mouse model. While the primary mechanism of cytotoxicity for 1 was consistent with ion leakage, we found that it was also able to directly depolarize mitochondria. Semisynthetic modification of 1 provided several analogs, including a C-terminus-linked coumarin derivative (22) that exhibited appreciably increased potency (GI50 5.4 ± 0.1 nM), but lacked ion leakage capabilities associated with a majority of naturally occurring peptaibols such as alamethicin. Compound 22 was found to enter intact cells and induced cell death in a process that was preceded by mitochondrial depolarization.

Original languageEnglish (US)
Pages (from-to)E8957-E8966
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number43
StatePublished - Oct 24 2017


  • Fungi
  • Gichigamin
  • Mitochondria
  • Natural products
  • Peptaibol

ASJC Scopus subject areas

  • General


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