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Catalases of Aspergillus fumigatus
Sophie Paris1, Deborah Wysong, Jean-Paul Debeaupuis
1Unité des Aspergillus, Département Structure et Dynamique des Gènômes, Institut Pasteur, Paris, France. sparis@pasteur.fr
Abstract:
Upon infection of a host, the pathogenic fungus Aspergillus fumigatus is attacked by the reactive oxygen species produced by phagocytic cells. Detoxification of hydrogen peroxide by catalases was proposed as a way to overcome this host response. A. fumigatus produces three active catalases; one is produced by conidia, and two are produced by mycelia. The mycelial catalase Cat1p was studied previously. Here we characterized the two other catalases, their genes, and the phenotypes of gene-disrupted mutants. CatAp, a spore-specific monofunctional catalase, is resistant to heat, metal ions, and detergent. This enzyme is a dimeric protein with 84.5-kDa subunits. The 749-amino-acid polypeptide exhibits high levels of similarity to the Aspergillus nidulans CatA catalase and to bacterial catalase HPII of Escherichia coli. In spite of increased sensitivity to H(2)O(2), killing of DeltacatA conidia by alveolar macrophages and virulence in animals were similar to the killing of conidia by alveolar macrophages and virulence in animals observed for the wild type. In contrast to the Cat1p and CatAp catalases, the mycelial Cat2p enzyme is a bifunctional catalase-peroxidase and is sensitive to heat, metal ions, and detergent. This enzyme, an 82-kDa monomer, is homologous to catalase-peroxidases of several fungi and bacteria. Surprisingly, mycelium of the double Deltacat1Deltacat2 mutant with no catalase activity exhibited only slightly increased sensitivity to H(2)O(2) and was as sensitive to killing by polymorphonuclear neutrophils as mycelium of the wild-type strain. However, this mutant exhibited delayed infection in the rat model of aspergillosis compared to infection by the wild-type strain. These results indicate that conidial catalase is not a virulence factor and that mycelial catalases transiently protect the fungus from the host.
Insights
Aspergillus fumigatus uses catalases to detoxify hydrogen peroxide from host immune cells. While spore catalase is not essential for virulence, mycelial catalases offer transient protection during infection.
Area of Science:
- Mycology
- Immunology
- Biochemistry
Background:
- Pathogenic fungus *Aspergillus fumigatus* encounters reactive oxygen species (ROS) from host phagocytic cells.
- Catalases are proposed to detoxify hydrogen peroxide (H₂O₂), a key ROS, aiding fungal survival.
- *A. fumigatus* produces three catalases: one in conidia and two in mycelia (Cat1p, Cat2p).
Purpose of the Study:
- To characterize the spore-specific catalase (CatAp) and the second mycelial catalase (Cat2p).
- To investigate the roles of these catalases in fungal resistance to host defenses and virulence.
- To analyze the phenotypes of gene-disrupted mutants lacking specific catalases.
Main Methods:
- Gene disruption to create single and double mutants (e.g., *DeltacatA*, *Deltacat1Deltacat2*).
- Biochemical characterization of purified catalases (CatAp, Cat2p).
- Assessment of fungal killing by alveolar macrophages and polymorphonuclear neutrophils.
- Evaluation of virulence in a rat model of aspergillosis.
Main Results:
- CatAp is a heat, metal ion, and detergent-resistant dimeric enzyme, homologous to *A. nidulans* CatA and bacterial HPII.
- *DeltacatA* conidia showed increased H₂O₂ sensitivity but similar macrophage killing and virulence.
- Cat2p is a heat, metal ion, and detergent-sensitive monomeric catalase-peroxidase, homologous to fungal and bacterial catalase-peroxidases.
- The double *Deltacat1Deltacat2* mutant showed only slightly increased H₂O₂ sensitivity and similar neutrophil killing.
- The double mutant exhibited delayed infection in a rat model, indicating a role for mycelial catalases in transient protection.
Conclusions:
- Conidial catalase (CatAp) is not a significant virulence factor for *A. fumigatus*.
- Mycelial catalases (Cat1p and Cat2p) provide transient protection against host immune responses during infection.
- Understanding these fungal defense mechanisms can inform strategies against aspergillosis.