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Nicotiana alata Defensin Chimeras Reveal Differences in the Mechanism of Fungal and Tumor Cell Killing and an Enhanced Antifungal Variant

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posted on 06.01.2021, 05:47 by Mark Bleackley, JAE Payne, Brigitte Hayes, T Durek, DJ Craik, Thomas Shafee, Ivan Poon, Mark Hulett, Nicole Van Der Weerden, Marilyn Anderson
Copyright © 2016, American Society for Microbiology. All Rights Reserved.

The plant defensin NaD1 is a potent antifungal molecule that also targets tumor cells with a high efficiency. We examined the features of NaD1 that contribute to these two activities by producing a series of chimeras with NaD2, a defensin that has relatively poor activity against fungi and no activity against tumor cells. All plant defensins have a common tertiary structure known as a cysteine-stabilized α-β motif which consists of an α helix and a triple-stranded β-sheet stabilized by four disulfide bonds. The chimeras were produced by replacing loops 1 to 7, the sequences between each of the conserved cysteine residues on NaD1, with the corresponding loops from NaD2. The loop 5 swap replaced the sequence motif (SKILRR) that mediates tight binding with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] and is essential for the potent cytotoxic effect of NaD1 on tumor cells. Consistent with previous reports, there was a strong correlation between PI(4,5)P2 binding and the tumor cell killing activity of all of the chimeras. However, this correlation did not extend to antifungal activity. Some of the loop swap chimeras were efficient antifungal molecules, even though they bound poorly to PI(4,5)P2, suggesting that additional mechanisms operate against fungal cells. Unexpectedly, the loop 1B swap chimera was 10 times more active than NaD1 against filamentous fungi. This led to the conclusion that defensin loops have evolved as modular components that combine to make antifungal molecules with variable mechanisms of action and that artificial combinations of loops can increase antifungal activity compared to that of the natural variants.

Funding

This work, including the efforts of Mark D. Hulett, Nicole L. van der Weerden, and Marilyn A. Anderson, was funded by Australian Research Council (ARC) (DP120102694). This work, including the efforts of Nicole L. van der Weerden and Marilyn A. Anderson, was funded by Australian Research Council (ARC) (DP150104386).

History

Publication Date

01/01/2016

Journal

Antimicrobial Agents and Chemotherapy

Volume

60

Issue

10

Pagination

11p. (p. 6302-6312)

Publisher

American Society for Microbiology

ISSN

1098-6596

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