Aspergillus fumigatus is the most common airborne fungal pathogen for humans. In this mold, iron starvation induces production of the siderophore triacetylfusarinine C (TAFC). Here we demonstrate a link between TAFC and ergosterol biosynthetic pathways, which are both critical for virulence and treatment of fungal infections. Consistent with mevalonate being a limiting prerequisite for TAFC biosynthesis, we observed increased expression of 3-hydroxy-3-methyl-glutaryl (HMG)-CoA reductase (Hmg1) under iron starvation, reduced TAFC biosynthesis following lovastatin-mediated Hmg1 inhibition, and increased TAFC biosynthesis following Hmg1 overexpression. We identified enzymes, the acyl-CoA ligase SidI and the enoyl-CoA hydratase SidH, linking biosynthesis of mevalonate and TAFC, deficiency of which under iron starvation impaired TAFC biosynthesis, growth, oxidative stress resistance, and murine virulence. Moreover, inactivation of these enzymes alleviated TAFC-derived biosynthetic demand for mevalonate, as evidenced by increased resistance to lovastatin. Concordant with bilateral demand for mevalonate, iron starvation decreased the ergosterol content and composition, a phenotype that is mitigated in TAFC-lacking mutants.siderophore | isoprenoide | statins

Siderophores play a central role in iron metabolism and virulence of most fungi. Both Aspergillus fumigatus and Aspergillus nidulans excrete the siderophore triacetylfusarinine C (TAFC) for iron acquisition. In A. fumigatus, green fluorescence protein-tagging revealed peroxisomal localization of the TAFC biosynthetic enzymes SidI (mevalonyl-CoA ligase), SidH (mevalonyl-CoA hydratase) and SidF (anhydromevalonyl-CoA transferase), while elimination of the peroxisomal targeting signal (PTS) impaired both, peroxisomal SidH-targeting and TAFC biosynthesis. The analysis of A. nidulans mutants deficient in peroxisomal biogenesis, ATP import or protein import revealed that cytosolic mislocalization of one or two but, interestingly, not all three enzymes impairs TAFC production during iron starvation. The PTS motifs are conserved in fungal orthologues of SidF, SidH and SidI. In agreement with the evolutionary conservation of the partial peroxisomal compartmentalization of fungal siderophore biosynthesis, the SidI orthologue of coprogen-type siderophore-producing Neurospora crassa was confirmed to be peroxisomal. Taken together, this study identified and characterized a novel, evolutionary conserved metabolic function of peroxisomes.

Siderophore-mediated iron handling is crucial for the virulence of Aspergillus fumigatus. Here we identified a new component of its siderophore metabolism, termed SidJ, which is encoded by AFUA_3G03390. The encoding gene is localized in a siderophore biosynthetic gene cluster that is conserved in a variety of fungi. During iron starvation, SidJ deficiency resulted in decreased growth and increased intracellular accumulation of hydrolysis products of the siderophore fusarinine C. The implied role in siderophore hydrolysis is consistent with a putative esterase domain in SidJ, which now represents the first functionally characterized member of the DUF1749 (domain of unknown function) protein family, with members found exclusively in fungi and plants.T he bioavailability of the essential nutrient iron is low, and therefore fungi have evolved various iron acquisition mechanisms, including siderophore-mediated iron uptake (1-3). The opportunistic fungal pathogen Aspergillus fumigatus produces four types of low-molecular-mass iron chelators, termed siderophores; it secretes fusarinine C (FSC) and triacetylfusarinine C (TAFC) for iron uptake and accumulates ferricrocin (FC) for hyphal iron distribution and storage and hydroxyferricrocin (HFC) for conidial iron distribution and storage (4, 5). FSC consists of three N 5 -anhydromevalonyl-N 5 -hydroxyornithine residues, termed fusarinine (FS), which is cyclically linked by ester bonds. TAFC is the N 2 -acetylated FSC. FC is a cyclic hexapeptide with the structure Gly-Ser-Gly-(N 5 -acetyl-N 5 -hydroxyornithine) 3 , and HFC is the hydroxylated FC (1). Both extra-and intracellular siderophores have been shown to be crucial for the virulence of A. fumigatus (4, 6). Subsequent to chelation of iron and uptake, FSC and TAFC are hydrolyzed and the iron is transferred to the metabolism or to the intracellular siderophore FC for transport and storage of iron (7,8). The esterase EstB was shown to be involved in the hydrolysis of TAFC, but not FSC, and consequently in the transfer of iron from TAFC to the metabolism and FC (8). In contrast, intracellular processing of FSC has remained enigmatic so far. Here we report the characterization of the FSC esterase SidJ.Under iron-sufficient conditions, siderophore production is repressed in A. fumigatus by the GATA transcription factor SreA (9). Genome-wide transcriptional profiling identified 49 SreA target genes, of which 13 have so far experimentally been proven to be involved in mechanisms for adaptation to iron starvation, such as reductive iron assimilation, siderophore metabolism, and iron regulation (10). Most of these genes are organized in gene clusters. The gene cluster encoding SidD (FSC nonribosomal peptide synthetase), SidF (hydroxyornithine transacylase), and SidH (mevalonyl-coenzyme A [CoA] hydratase), which are all essential for the biosynthesis of FSC and TAFC, also contains the so far uncharacterized gene AFUA_3G03390 (10) (see Fig. S1 in the supplemental material). The deduced protein, termed SidJ, consists of 354 amino ...