Identification of a Hybrid PKS/NRPS Required for Pseurotin A Biosynthesis in the Human Pathogen Aspergillus fumigatus

Abstract

The genome sequence of Aspergillus fumigatus revealed the presence of a single hybrid polyketide synthase-non-ribosomal peptide synthetase (PKS/NRPS) gene that is present within a cluster of five genes suggestive of its involvement in secondary metabolism. Here, we present evidence that it is required for the biosynthesis of pseurotin A, a compound with an unusual heterospirocyclic gamma-lactam structure. We have confirmed that the genome reference strain A. fumigatus Af293 produces pseurotin A, a compound previously reported to be a competitive inhibitor of chitin synthase and an inducer of nerve-cell proliferation. Deletion or overexpression of the PKS/NRPS gene psoA in A. fumigatus leads to the absence or accumulation of pseurotin A, respectively; this indicates that this gene is essential for the biosynthesis of pseurotin A. It is likely that the first product of psoA is converted to pseurotin A by the products of other genes in this cluster.

Global Transcriptome Changes Underlying Colony Growth in the Opportunistic Human Pathogen Aspergillus fumigatus

“…4; also see Table S6). Most noticeably, 44 of the 62 genes in the fumitremorgin supercluster (55), which encodes enzymes that produce fumitremorgin and pseurotin A as well as an unknown compound (36,37,55), were upregulated (32 genes) or uniquely expressed (12 genes). Within this supercluster, the putative O-methyltransferase CalO6 (Afu8g00200) was the most upregulated gene in the genome, showing a 9,885-fold upregulation in BF relative to PL.…”

“…3 and 4). This cluster codes for an unknown compound, as well as the known toxins fumitremorgin (36), a tremorginic mycotoxin capable of inhibiting cell cycle in mammals, and pseurotin A, a neuritogenic compound and chitinase inhibitor (37). Additionally, we observed an upregulation of an entire gene cluster coding for a trichothecene mycotoxin, a compound that can inhibit protein synthesis in eukaryotes (4).…”

Multiplexed Activity-based Protein Profiling of the Human Pathogen Aspergillus fumigatus Reveals Large Functional Changes upon Exposure to Human Serum

“…4 and supplemental Table S8). Five proteins with a Ͼ15-fold change are annotated with secondary metabolism function ( Table 2): catalase fgaCat (AFUA_2G18030), active in fumigaclavine C biosynthesis (40), two melanin conidial pigment biosynthetic proteins Arp2 (AFUA_2G17560) and Ayg1 (AFUA_2G17550) (41), hybrid PKS-NRPS enzyme nrps14 (AFUA_8G00540) of the pseurotin A biosynthesis gene cluster (42), and glutathione S-transferase (AFUA_4G14380) located on chromosome 4 near other secondary metabolite biosynthesis gene clusters (Table 2) (43). Transcription of fgaCat, nrps14, and the glutathione S-transferase changed in the presence of voriconazole (44) and/or hypoxic conditions (45).…”

A Novel Type Pathway-Specific Regulator and Dynamic Genome Environments of a Solanapyrone Biosynthesis Gene Cluster in the Fungus Ascochyta rabiei

“…These plastic chromosomal regions often include contingency genes, such as genes involved in membrane transport (2, 6), nutrient assimilation (2, 7), anaerobiosis (8), and virulence (1, 9, 10). Secondary metabolite (SM) gene clusters also exhibit a subtelomeric bias (11)(12)(13)(14).In fungi, SMs play diverse roles in host and niche specialization, serving as virulence factors, antibiotics, and metal ionchelating agents (15, 16). Solanapyrones are polyketide-derived SMs that were originally found in the plant-pathogenic fungi Alternaria solani and Ascochyta rabiei (17, 18), as well as in some other ascomycetous fungi occupying different ecological niches (19-21).…”