Novel molecular mechanisms of iron sensing and homeostasis in filamentous fungi
Final Report Abstract
Iron is essential for numerous cellular processes but toxic in excess. Moreover, adaptation to iron starvation is a crucial virulence determinant of pathogens including fungi. Due to the fundamental differences in the mechanism employed by host and pathogens to maintain iron homeostasis, iron metabolism is an attractive new target for improvement of antifungal therapy and diagnosis of fungal infections. However, a better understanding of the molecular basis of fungal iron homeostasis is required. In various fungi including the most common airborne fungal pathogen Aspergillus fumigatus, the key iron regulator HapX was shown to be required for adaptation to iron starvation via its interaction with the CCAAT-binding complex (CBC). This collaborative study combining genetics, biochemistry and structural biology as well as in vitro and in vivo analyses revealed that the HapX:CBC complex additionally regulates iron resistance. Furthermore, we elucidated the molecular mechanisms underlying HapX-mediated iron-sensing and iron-regulation. For instance, we (i) identified HapX protein domains that are important for adaptation to iron starvation and iron resistance, respectively, (ii) elucidated the mode of DNA-binding by the HapX-CBC complex using X-ray crystallography and ChIP-seq, (iii) identified cellular components required for iron sensing (monothiol glutaredoxin D and glutathione), and (iv) demonstrated that iron sensing requires a signal derived from mitochondrial iron-sulfur-cluster biosynthesis. Moreover, we functionally and structurally characterized several cellular components involved in iron homeostasis maintenance. Furthermore, our studies identified and analyzed links between iron regulation with secondary metabolism, ergosterol biosynthesis, azole resistance, leucine biosynthesis, microbial interaction, and mammalian virulence. Taken together, this project revealed similarities but also significant differences in iron sensing and regulation between the ascomycete pathogen A. fumigatus and other model fungal species, which might be exploited in antifungal therapy as well as in biotechnology. The results of this study, reflected by the publication output, emphasize the successful collaboration within the D-A-CH consortium as well as with other national and international partners.
Publications
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(2014). The Janus transcription factor HapX controls fungal adaptation to both iron starvation and iron excess. EMBO J. 33:2261-76
Gsaller F, Hortschansky P, Beattie SR, Klammer K, Tuppatsch K, Lechner BE, Rietzschel N, Werner ER, Vogan AA, Chung D, Mühlenhoff U, Kato M, Cramer RA, Brakhage AA, Haas H
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(2015). Deciphering the combinatorial DNA-binding code of the CCAAT-binding complex and the iron-regulatory basic region leucine zipper (bZIP) transcription factor HapX. J Biol Chem. 290:6058-70
Hortschansky P, Ando E, Tuppatsch K, Arikawa T, Kobayashi T, Kato M, Haas H, Brakhage AA
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(2016). Sterol biosynthesis and azole tolerance is governed by the opposing actions of SrbA and the CCAAT binding complex. PLoS Pathog. 12(7):e1005775
Gsaller F, Hortschansky P, Furukawa T, Carr PD, Rash B, Capilla J, Müller C, Bracher F, Bowyer P, Haas H, Brakhage AA, Bromley MJ
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(2017). The CCAAT-binding (CBC) complex in Aspergillus species. Biochim Biophys Acta Gene Regul Mech. 1860:560-570
Hortschansky P, Haas H, Huber EM, Groll M, Brakhage AA
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(2019). The monothiol glutaredoxin GrxD is essential for sensing iron starvation in Aspergillus fumigatus. PLoS Genet. 15(9):e1008379
Misslinger M, Scheven MT, Hortschansky P, López-Berges MS, Heiss K, Beckmann N, Heigl T, Hermann M, Krüger T, Kniemeyer O, Brakhage AA, Haas H
