Self-protection against gliotoxin--a component of the gliotoxin biosynthetic cluster, GliT, completely protects Aspergillus fumigatus against exogenous gliotoxin.
Self-protection against gliotoxin--a component of the gliotoxin biosynthetic cluster, GliT, completely protects Aspergillus fumigatus against exogenous gliotoxin.
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DOI：
10.1371/journal.ppat.1000952
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发表时间：
2010-06-10
期刊：
影响因子：
6.7
通讯作者：
Doyle S
中科院分区：
文献类型：
--
作者：
Schrettl M;Carberry S;Kavanagh K;Haas H;Jones GW;O'Brien J;Nolan A;Stephens J;Fenelon O;Doyle S
胶霉毒素和其他相关分子由多基因簇编码，并由真菌利用非核糖体生物合成机制生物合成。胶霉毒素几乎普遍被描述为对哺乳动物细胞的毒性，它已被认为是烟曲霉毒力库的一个组成部分。在这里，我们发现，在两个烟曲霉菌株的胶霉毒素生物合成簇中删除单个基因gliT，使生物体对外源胶霉毒素高度敏感，并完全破坏胶霉毒素的分泌。向两种烟曲霉ΔgliT菌株添加谷胱甘肽可缓解胶霉毒素抑制。此外，与所有其他簇成分相比，gliT 的表达似乎是独立调节的，并且在转录物和蛋白质水平上均因外源胶霉毒素的存在而上调。接触胶霉毒素后，gliT 也在烟曲霉 ΔgliZ 中表达，而烟曲霉 ΔgliZ 不能表达胶霉毒素生物合成簇中的任何其他基因，表明 gliT 主要负责保护该菌株免受外源胶霉毒素的侵害。 GliT 的胶霉毒素还原酶活性高达 9 µM 胶霉毒素，并且似乎可以通过还原氧化形式的胶霉毒素来防止细胞内谷胱甘肽储备的不可逆消耗。当用 gliT 转化时，构巢曲霉和酿酒酵母分别获得了对外源胶霉毒素的跨物种抗性。我们假设胶霉毒素的主要作用可能是作为抗氧化剂，除了 GliT 功能之外，胶霉毒素的分泌可能是自身保护机制的一个组成部分，烟曲霉利用该机制来保护自身免受这种强效生物分子的侵害。致病真菌烟曲霉会导致免疫功能低下的个体（例如癌症患者）患病。这种真菌会产生一种叫做胶霉毒素的小分子，它可以帮助烟曲霉绕过病人的免疫系统，从而引起疾病。尽管胶霉毒素是一种小分子，但它的生物合成是通过一系列复杂的酶实现的，其中一种在烟曲霉中被称为 GliT。令人惊讶的是，没有人真正考虑过胶霉毒素可能对烟曲霉本身有毒。在这里，我们发现，GliT 的缺失使得烟曲霉对添加的胶霉毒素高度敏感并抑制真菌生长，这两种情况都可以通过恢复 GliT 来逆转。当 GliT 缺失时，真菌也不能制造或释放自己的胶霉毒素。我们还表明，通过添加谷胱甘肽可以完全克服胶霉毒素敏感性，谷胱甘肽是细胞内重要的抗氧化剂。我们证明添加胶霉毒素会增加 GliT 的产生，并且 GliT 会破坏胶霉毒素中的二硫键，这可能是烟曲霉保护或释放胶霉毒素途径中的一个步骤。我们得出结论，胶霉毒素可能主要参与保护烟曲霉免受氧化应激，并且它是一种偶然毒素。
Gliotoxin, and other related molecules, are encoded by multi-gene clusters and biosynthesized by fungi using non-ribosomal biosynthetic mechanisms. Almost universally described in terms of its toxicity towards mammalian cells, gliotoxin has come to be considered as a component of the virulence arsenal of Aspergillus fumigatus. Here we show that deletion of a single gene, gliT, in the gliotoxin biosynthetic cluster of two A. fumigatus strains, rendered the organism highly sensitive to exogenous gliotoxin and completely disrupted gliotoxin secretion. Addition of glutathione to both A. fumigatus ΔgliT strains relieved gliotoxin inhibition. Moreover, expression of gliT appears to be independently regulated compared to all other cluster components and is up-regulated by exogenous gliotoxin presence, at both the transcript and protein level. Upon gliotoxin exposure, gliT is also expressed in A. fumigatus ΔgliZ, which cannot express any other genes in the gliotoxin biosynthetic cluster, indicating that gliT is primarily responsible for protecting this strain against exogenous gliotoxin. GliT exhibits a gliotoxin reductase activity up to 9 µM gliotoxin and appears to prevent irreversible depletion of intracellular glutathione stores by reduction of the oxidized form of gliotoxin. Cross-species resistance to exogenous gliotoxin is acquired by A. nidulans and Saccharomyces cerevisiae, respectively, when transformed with gliT. We hypothesise that the primary role of gliotoxin may be as an antioxidant and that in addition to GliT functionality, gliotoxin secretion may be a component of an auto-protective mechanism, deployed by A. fumigatus to protect itself against this potent biomolecule. The pathogenic fungus Aspergillus fumigatus causes disease in immunocompromised individuals such as cancer patients. The fungus makes a small molecule called gliotoxin which helps A. fumigatus bypass the immune system in ill people, and cause disease. Although a small molecule, gliotoxin biosynthesis is enabled by a complex series of enzymes, one of which is called GliT, in A. fumigatus. Amazingly, nobody has really considered that gliotoxin might be toxic to A. fumigatus itself. Here we show that absence of GliT makes A. fumigatus highly sensitive to added gliotoxin and inhibits fungal growth, both of which can be reversed by restoring GliT. Neither can the fungus make or release its own gliotoxin when GliT is missing. We also show that gliotoxin sensitivity can be totally overcome by adding glutathione, which is an important anti-oxidant within cells. We demonstrate that gliotoxin addition increases the production of GliT, and that GliT breaks the disulphide bond in gliotoxin which may be a step in the pathway for gliotoxin protection or release from A. fumigatus. We conclude that gliotoxin may mainly be involved in protecting A. fumigatus against oxidative stress and that it is an accidental toxin.
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DOI：
10.1016/j.bbrc.2007.05.139
发表时间：
2007-08-03
影响因子：
3.1
作者：
Choi, Hee Shim;Shim, Joong Sup;Kwon, Ho Jeong
通讯作者：
Kwon, Ho Jeong
影响因子：
3.6
作者：
Kupfahl, Claudio;Heinekamp, Thorsten;Brakhage, Axel A.
通讯作者：
Brakhage, Axel A.
DOI：
10.1016/j.bbrc.2006.01.078
发表时间：
2006-03-24
影响因子：
3.1
作者：
Carberry, S;Neville, CM;Doyle, S
通讯作者：
Doyle, S
影响因子：
4.9
作者：
Chamilos, Georgios;Lewis, Russell E.;Kontoyiannis, Dimitrios P.
通讯作者：
Kontoyiannis, Dimitrios P.
影响因子：
2.9
作者：
Hill, KE;McCollum, GW;Burk, RF
通讯作者：
Burk, RF