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Happacher I, Aguiar M, Alilou M, Abt B, Baltussen TJH, Decristoforo C, Melchers WJG, Haas H. The Siderophore Ferricrocin Mediates Iron Acquisition in Aspergillus fumigatus. Microbiol Spectr 2023; 11:e0049623. [PMID: 37199664 PMCID: PMC10269809 DOI: 10.1128/spectrum.00496-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Accepted: 04/28/2023] [Indexed: 05/19/2023] Open
Abstract
The opportunistic fungal pathogen Aspergillus fumigatus utilizes two high-affinity iron uptake mechanisms, termed reductive iron assimilation (RIA) and siderophore-mediated iron acquisition (SIA). The latter has been shown to be crucial for virulence of this fungus and is a target for development of novel strategies for diagnosis and treatment of fungal infections. So far, research on SIA in this mold focused mainly on the hyphal stage, revealing the importance of extracellular fusarinine-type siderophores in iron acquisition as well as of the siderophore ferricrocin in intracellular iron handling. The current study aimed to characterize iron acquisition during germination. High expression of genes involved in biosynthesis and uptake of ferricrocin in conidia and during germination, independent of iron availability, suggested a role of ferricrocin in iron acquisition during germination. In agreement, (i) bioassays indicated secretion of ferricrocin during growth on solid media during both iron sufficiency and limitation, (ii) ferricrocin was identified in the supernatant of conidia germinating in liquid media during both iron sufficiency and limitation, (iii) in contrast to mutants lacking all siderophores, mutants synthesizing ferricrocin but lacking fusarinine-type siderophores were able to grow under iron limitation in the absence of RIA, and (iv) genetic inactivation of the ferricrocin transporter Sit1 decreased germination in the absence of RIA. Taken together, this study revealed that ferricrocin has not only an intracellular role but also functions as an extracellular siderophore to support iron acquisition. The iron availability-independent ferricrocin secretion and uptake during early germination indicate developmental, rather than iron regulation. IMPORTANCE Aspergillus fumigatus is one of the most common airborne fungal pathogens for humans. Low-molecular-mass iron chelators, termed siderophores, have been shown to play a central role in iron homeostasis and, consequently, virulence of this mold. Previous studies demonstrated the crucial role of secreted fusarinine-type siderophores, such as triacetylfusarinine C, in iron acquisition, as well as of the ferrichrome-type siderophore ferricrocin in intracellular iron storage and transport. Here, we demonstrate that ferricrocin is also secreted to mediate iron acquisition during germination together with reductive iron assimilation. During early germination, ferricrocin secretion and uptake were not repressed by iron availability, indicating developmental regulation of this iron acquisition system in this growth phase.
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Affiliation(s)
- Isidor Happacher
- Institute of Molecular Biology, Biocenter, Medical University Innsbruck, Innsbruck, Austria
| | - Mario Aguiar
- Institute of Molecular Biology, Biocenter, Medical University Innsbruck, Innsbruck, Austria
| | - Mostafa Alilou
- Institute of Pharmacy, Unit of Pharmacognosy, Center for Molecular Biosciences Innsbruck, Austria
| | - Beate Abt
- Institute of Molecular Biology, Biocenter, Medical University Innsbruck, Innsbruck, Austria
| | - Tim J. H. Baltussen
- Department of Medical Microbiology, Radboud University Medical Centre, Nijmegen, The Netherlands
- Centre of Expertise in Mycology, Radboudumc/CWZ, Nijmegen, The Netherlands
| | - Clemens Decristoforo
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria
| | - Willem J. G. Melchers
- Department of Medical Microbiology, Radboud University Medical Centre, Nijmegen, The Netherlands
- Centre of Expertise in Mycology, Radboudumc/CWZ, Nijmegen, The Netherlands
| | - Hubertus Haas
- Institute of Molecular Biology, Biocenter, Medical University Innsbruck, Innsbruck, Austria
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Aguiar M, Orasch T, Shadkchan Y, Caballero P, Pfister J, Sastré-Velásquez LE, Gsaller F, Decristoforo C, Osherov N, Haas H. Uptake of the Siderophore Triacetylfusarinine C, but Not Fusarinine C, Is Crucial for Virulence of Aspergillus fumigatus. mBio 2022; 13:e0219222. [PMID: 36125294 PMCID: PMC9600649 DOI: 10.1128/mbio.02192-22] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 09/02/2022] [Indexed: 11/20/2022] Open
Abstract
Siderophores play an important role in fungal virulence, serving as trackers for in vivo imaging and as biomarkers of fungal infections. However, siderophore uptake is only partially characterized. As the major cause of aspergillosis, Aspergillus fumigatus is one of the most common airborne fungal pathogens of humans. Here, we demonstrate that this mold species mediates the uptake of iron chelated by the secreted siderophores triacetylfusarinine C (TAFC) and fusarinine C by the major facilitator-type transporters MirB and MirD, respectively. In a murine aspergillosis model, MirB but not MirD was found to be crucial for virulence, indicating that TAFC-mediated uptake plays a dominant role during infection. In the absence of MirB, TAFC becomes inhibitory by decreasing iron availability because the mutant is not able to recognize iron that is chelated by TAFC. MirB-mediated transport was found to tolerate the conjugation of fluorescein isothiocyanate to triacetylfusarinine C, which might aid in the development of siderophore-based antifungals in a Trojan horse approach, particularly as the role of MirB in pathogenicity restrains its mutational inactivation. Taken together, this study identified the first eukaryotic siderophore transporter that is crucial for virulence and elucidated its translational potential as well as its evolutionary conservation. IMPORTANCE Aspergillus fumigatus is responsible for thousands of cases of invasive fungal disease annually. For iron uptake, A. fumigatus secretes so-called siderophores, which are taken up after the binding of environmental iron. Moreover, A. fumigatus can utilize siderophore types that are produced by other fungi or bacteria. Fungal siderophores raised considerable interest due to their role in virulence and their potential for the diagnosis and treatment of fungal infections. Here, we demonstrate that the siderophore transporter MirB is crucial for the virulence of A. fumigatus, which reveals that its substrate, triacetylfusarinine C, is the most important siderophore during infection. We found that in the absence of MirB, TAFC becomes inhibitory by decreasing the availability of environmental iron and that MirB-mediated transport tolerates the derivatization of its substrate, which might aid in the development of siderophore-based antifungals. This study significantly improved the understanding of fungal iron homeostasis and the role of siderophores in interactions with the host.
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Affiliation(s)
- Mario Aguiar
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Thomas Orasch
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Yana Shadkchan
- Department of Clinical Microbiology and Immunology, Sackler School of Medicine Ramat-Aviv, Tel Aviv, Israel
| | - Patricia Caballero
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Joachim Pfister
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria
| | | | - Fabio Gsaller
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
| | - Clemens Decristoforo
- Department of Nuclear Medicine, Medical University Innsbruck, Innsbruck, Austria
| | - Nir Osherov
- Department of Clinical Microbiology and Immunology, Sackler School of Medicine Ramat-Aviv, Tel Aviv, Israel
| | - Hubertus Haas
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, Innsbruck, Austria
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Aguiar M, Orasch T, Misslinger M, Dietl AM, Gsaller F, Haas H. The Siderophore Transporters Sit1 and Sit2 Are Essential for Utilization of Ferrichrome-, Ferrioxamine- and Coprogen-Type Siderophores in Aspergillus fumigatus. J Fungi (Basel) 2021; 7:768. [PMID: 34575806 PMCID: PMC8470733 DOI: 10.3390/jof7090768] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Revised: 09/13/2021] [Accepted: 09/14/2021] [Indexed: 11/18/2022] Open
Abstract
Siderophore-mediated acquisition of iron has been shown to be indispensable for the virulence of several fungal pathogens, the siderophore transporter Sit1 was found to mediate uptake of the novel antifungal drug VL-2397, and siderophores were shown to be useful as biomarkers as well as for imaging of fungal infections. However, siderophore uptake in filamentous fungi is poorly characterized. The opportunistic human pathogen Aspergillus fumigatus possesses five putative siderophore transporters. Here, we demonstrate that the siderophore transporters Sit1 and Sit2 have overlapping, as well as unique, substrate specificities. With respect to ferrichrome-type siderophores, the utilization of ferrirhodin and ferrirubin depended exclusively on Sit2, use of ferrichrome A depended mainly on Sit1, and utilization of ferrichrome, ferricrocin, and ferrichrysin was mediated by both transporters. Moreover, both Sit1 and Sit2 mediated use of the coprogen-type siderophores coprogen and coprogen B, while only Sit1 transported the bacterial ferrioxamine-type xenosiderophores ferrioxamines B, G, and E. Neither Sit1 nor Sit2 were important for the utilization of the endogenous siderophores fusarinine C and triacetylfusarinine C. Furthermore, A. fumigatus was found to lack utilization of the xenosiderophores schizokinen, basidiochrome, rhizoferrin, ornibactin, rhodotorulic acid, and enterobactin. Taken together, this study characterized siderophore use by A. fumigatus and substrate characteristics of Sit1 and Sit2.
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Affiliation(s)
| | | | | | | | | | - Hubertus Haas
- Institute of Molecular Biology/Biocenter, Medical University of Innsbruck, A-6020 Innsbruck, Austria; (M.A.); (T.O.); (M.M.); (A.-M.D.); (F.G.)
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Misslinger M, Petrik M, Pfister J, Hubmann I, Bendova K, Decristoforo C, Haas H. Desferrioxamine B-Mediated Pre-Clinical In Vivo Imaging of Infection by the Mold Fungus Aspergillus fumigatus. J Fungi (Basel) 2021; 7:734. [PMID: 34575772 PMCID: PMC8472378 DOI: 10.3390/jof7090734] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Revised: 08/26/2021] [Accepted: 09/04/2021] [Indexed: 12/16/2022] Open
Abstract
Fungal infections are a serious threat, especially for immunocompromised patients. Early and reliable diagnosis is crucial to treat such infections. The bacterially produced siderophore desferrioxamine B (DFO-B) is utilized by a variety of microorganisms for iron acquisition, while mammalian cells lack the uptake of DFO-B chelates. DFO-B is clinically approved for a variety of long-term chelation therapies. Recently, DFO-B-complexed gallium-68 ([68Ga]Ga-DFO-B) was shown to enable molecular imaging of bacterial infections by positron emission tomography (PET). Here, we demonstrate that [68Ga]Ga-DFO-B can also be used for the preclinical molecular imaging of pulmonary infection caused by the fungal pathogen Aspergillus fumigatus in a rat aspergillosis model. Moreover, by combining in vitro uptake studies and the chemical modification of DFO-B, we show that the cellular transport efficacy of ferrioxamine-type siderophores is impacted by the charge of the molecule and, consequently, the environmental pH. The chemical derivatization has potential implications for its diagnostic use and characterizes transport features of ferrioxamine-type siderophores.
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Affiliation(s)
- Matthias Misslinger
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, 6020 Innsbruck, Austria;
| | - Milos Petrik
- Institute of Molecular and Translational Medicine, Faculty of Medicine and Dentistry, Palacky University, 77900 Olomouc, Czech Republic; (M.P.); (K.B.)
| | - Joachim Pfister
- Department of Nuclear Medicine, Medical University of Innsbruck, 6020 Innsbruck, Austria; (J.P.); (I.H.)
| | - Isabella Hubmann
- Department of Nuclear Medicine, Medical University of Innsbruck, 6020 Innsbruck, Austria; (J.P.); (I.H.)
| | - Katerina Bendova
- Institute of Molecular and Translational Medicine, Faculty of Medicine and Dentistry, Palacky University, 77900 Olomouc, Czech Republic; (M.P.); (K.B.)
| | - Clemens Decristoforo
- Department of Nuclear Medicine, Medical University of Innsbruck, 6020 Innsbruck, Austria; (J.P.); (I.H.)
| | - Hubertus Haas
- Institute of Molecular Biology, Biocenter, Medical University of Innsbruck, 6020 Innsbruck, Austria;
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Bartho JD, Demitri N, Bellini D, Flachowsky H, Peil A, Walsh MA, Benini S. The structure of Erwinia amylovora AvrRpt2 provides insight into protein maturation and induced resistance to fire blight by Malus × robusta 5. J Struct Biol 2019; 206:233-242. [PMID: 30928616 DOI: 10.1016/j.jsb.2019.03.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2019] [Revised: 03/25/2019] [Accepted: 03/26/2019] [Indexed: 10/27/2022]
Abstract
The AvrRpt2 protein of the phytopathogenic bacterium Erwinia amylovora (AvrRpt2EA) is a secreted type III effector protein, which is recognised by the FB_MR5 resistance protein of Malus × robusta 5, the only identified resistance protein from a Malus species preventing E. amylovora infection. The crystal structure of the immature catalytic domain of AvrRpt2EA, a C70 family cysteine protease and type III effector, was determined to a resolution of 1.85 Å. The structure provides insights into the cyclophilin-dependent activation of AvrRpt2, and identifies a cryptic leucine of a non-canonical cyclophilin binding motif. The structure also suggests that residue Cys156, responsible for the gene induced resistance, is not involved in substrate determination, and hints that recognition by FB_MR5 is due to direct interaction.
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Affiliation(s)
- Joseph D Bartho
- Bioorganic Chemistry and Bio-Crystallography Laboratory (B(2)Cl), Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, 39100 Bolzano, Italy
| | - Nicola Demitri
- Elettra - Sincrotrone Trieste, S.S 14 km 163.5 in Area Science Park, Basovizza, Trieste 34149, Italy
| | - Dom Bellini
- Diamond Light Source LTD, Harwell Science and Innovation Campus, Didcot OX11 0QX, United Kingdom; Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot OX11 0FA, United Kingdom
| | - Henryk Flachowsky
- Julius Kühn-Institut, Federal Research Centre for Cultivated Plants, Institute for Breeding Research on Fruit Crops, Pillnitzer Platz 3a, D-01326 Dresden, Germany
| | - Andreas Peil
- Julius Kühn-Institut, Federal Research Centre for Cultivated Plants, Institute for Breeding Research on Fruit Crops, Pillnitzer Platz 3a, D-01326 Dresden, Germany
| | - Martin A Walsh
- Diamond Light Source LTD, Harwell Science and Innovation Campus, Didcot OX11 0QX, United Kingdom; Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot OX11 0FA, United Kingdom
| | - Stefano Benini
- Bioorganic Chemistry and Bio-Crystallography Laboratory (B(2)Cl), Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, 39100 Bolzano, Italy.
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