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Proc Natl Acad Sci U S A. 2017 Oct 24;114(43):E8957-E8966. doi: 10.1073/pnas.1707565114. Epub 2017 Oct 10.

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

Author information

1
Department of Chemistry and Biochemistry, Stephenson Life Sciences Research Center, University of Oklahoma, Norman, OK 73019-5251.
2
Natural Products Discovery Group, Institute for Natural Products Applications and Research Technologies, University of Oklahoma, Norman, OK 73019-5251.
3
Department of Pharmacology, University of Texas Health Science Center, San Antonio, TX 78229.
4
Cancer Therapy & Research Center, University of Texas Health Science Center, San Antonio, TX 78229.
5
Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK 73019-5251.
6
Department of Physiology, School of Medicine, University of Texas Health Science Center, San Antonio, TX 78229.
7
Department of Biochemistry, High Throughput Screening Facility, Center for Innovative Drug Discovery, University of Texas Health Science Center, San Antonio, TX 78229.
8
CytoBioscience Incorporated, San Antonio, TX 78229.
9
Department of Chemistry and Biochemistry, Stephenson Life Sciences Research Center, University of Oklahoma, Norman, OK 73019-5251; rhcichewicz@ou.edu.

Abstract

Mass-spectrometry-based metabolomics and molecular phylogeny data were used to identify a metabolically prolific strain of Tolypocladium that 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.

KEYWORDS:

fungi; gichigamin; mitochondria; natural products; peptaibol

PMID:
29073092
PMCID:
PMC5664515
DOI:
10.1073/pnas.1707565114
[Indexed for MEDLINE]
Free PMC Article

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