Aspergillus fumigatus SidJ Mediates Intracellular Siderophore Hydrolysis

Abstract

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 ...

Secondary metabolite arsenal of an opportunistic pathogenic fungus

“…The two siderophore BGCs are not presented as such, but can be pieced together from several studies to yield a two-gene ferricrocin cluster composed of SidI and SidC [33,34] and a six-gene fusarinine C cluster (composed of SidJ, SidF, SidH, SidD, SitT and MirD [34][35][36][37][38]). Additional BGCs can be inferred from orthology to known clusters in other fungi including the conserved nidulanin A BGC described in A. nidulans [39], a fusarielin-like cluster described in Fusarium graminearum [40], and a fumonisin-like cluster (fumonisin is synthesized by many Fusarium spp.)…”

Intracellular siderophore but not extracellular siderophore is required for full virulence in Metarhizium robertsii

“…mrsidC is located between a putative glycine-betaine biosynthesis cluster (badA and codA, (Lambou et al, 2013)), one of 2 candidate orthologs of the triacetylfusarinine esterase sidJ on one side and sidA (L-ornithine N5-monooxygenase) ortholog on the other (Supplementary Fig. S1A) (Grundlinger et al, 2013).…”

Eisenaufnahme in Pilzen der Gattung Aspergillus: strukturelle und biochemische Einblicke in Siderophoresterasen

“…[13] Vergleiche zwischen Strukturen und Substratspezifitäten legen nahe,d ass eine kleine Insertion in AnEstA und die Ungeachtet der strukturellen Übereinstimmung beider EstB-Proteine fallen signifikante Abweichungen in den katalytischen Parametern auf.D ies kçnnte Unterschiede im Siderophormetabolismus selbst zwischen eng verwandten Pilzspezies andeuten.…”