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    Interplay between Gliotoxin Resistance, Secretion, and the Methyl/ Methionine Cycle in Aspergillus fumigatus


    Owens, Rebecca A. and O'Keeffe, Grainne and Smith, Elizabeth B. and Dolan, Stephen K. and Hammel, Stephen and Sheridan, Kevin J. and Fitzpatrick, David A. and Keane, Thomas M. and Doyle, Sean (2015) Interplay between Gliotoxin Resistance, Secretion, and the Methyl/ Methionine Cycle in Aspergillus fumigatus. Eukaryotic Cell, 14 (9). pp. 941-957. ISSN 1535-9786

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    Abstract

    Mechanistic studies on gliotoxin biosynthesis and self-protection in Aspergillus fumigatus, both of which require the gliotoxin oxidoreductase GliT, have revealed a rich landscape of highly novel biochemistries, yet key aspects of this complex molecular architecture remain obscure. Here we show that an A. fumigatus ∆gliA strain is completely deficient in gliotoxin secretion but still retains the ability to efflux bisdethiobis(methylthio)gliotoxin (BmGT). This correlates with a significant increase in sensitivity to exogenous gliotoxin because gliotoxin trapped inside the cell leads to (i) activation of the gli cluster, as disabling gli cluster activation, via gliZ deletion, attenuates the sensitivity of an A. fumigatus ∆gliT strain to gliotoxin, thus implicating cluster activation as a factor in gliotoxin sensitivity, and (ii) increased methylation activity due to excess substrate (dithiol gliotoxin) for the gliotoxin bis-thiomethyltransferase GtmA. Intracellular dithiol gliotoxin is oxidized by GliT and subsequently effluxed by GliA. In the absence of GliA, gliotoxin persists in the cell and is converted to BmGT, with levels significantly higher than those in the wild type. Similarly, in the ∆gliT strain, gliotoxin oxidation is impeded, and methylation occurs unchecked, leading to significant S-adenosylmethionine (SAM) depletion and S-adenosylhomocysteine (SAH) overproduction. This in turn significantly contributes to the observed hypersensitivity of gliT-deficient A. fumigatus to gliotoxin. Our observations reveal a key role for GliT in preventing dysregulation of the methyl/methionine cycle to control intracellular SAM and SAH homeostasis during gliotoxin biosynthesis and exposure. Moreover, we reveal attenuated GliT abundance in the A. fumigatus ∆gliK strain, but not the ∆gliG strain, following exposure to gliotoxin, correlating with relative sensitivities. Overall, we illuminate new systems interactions that have evolved in gliotoxin-producing, compared to gliotoxin-naive, fungi to facilitate their cellular presence.

    Item Type: Article
    Additional Information: This article is available at Owens RA, O’Keeffe G, Smith EB, Dolan SK, Hammel S, Sheridan KJ, Fitzpatrick DA, Keane TM, Jones GW, Doyle S. 2015. Interplay between gliotoxin resistance, secretion, and the methyl/methionine cycle in Aspergillus fumigatus. Eukaryot Cell 14:941–957. doi:10.1128/EC.00055-15.
    Keywords: Gliotoxin Resistance; Secretion; Methyl/ Methionine Cycle; Aspergillus fumigatus;
    Academic Unit: Faculty of Science and Engineering > Biology
    Item ID: 6338
    Identification Number: https://doi.org/10.1128/EC.00055-15
    Depositing User: Dr. Sean Doyle
    Date Deposited: 07 Sep 2015 15:34
    Journal or Publication Title: Eukaryotic Cell
    Publisher: American Society for Microbiology
    Refereed: Yes
    Funders: Science Foundation Ireland (SFI), Higher Education Authority (HEA), Irish Research Council
    URI:

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