Catalases of Aspergillus fumigatus

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 ⌬catA 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 ⌬cat1⌬cat2 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.The opportunistic fungal pathogen Aspergillus fumigatus is responsible for a variety of respiratory diseases in humans, such as allergic bronchopulmonary aspergillosis, aspergilloma, and invasive aspergillosis (10). This fungus is an airborne saprophyte that is inhaled by every human. Alveolar macrophages and polymorphonuclear cells, cellular components of the innate defense of the lung, cooperate to control and eliminate the fungus in the airways. Macrophages eliminate conidia, and protection against the hyphal form is mediated by polymorphonuclear cells (41). Reactive oxygen species (ROS) produced by alveolar macrophages play an essential role in the killing of A. fumigatus conidia (38a). Moreover, in vitro studies of neutrophil function have shown that hydrogen peroxide effectively kills fungal hyphae (12) and that neutrophil-mediated damage is blocked by addition of a commercial catalase (13). Accordingly, catalase, which is a good scavenger of H 2 O 2 , was considered to be a putative virulence factor of A. fumigatus that could counteract the oxidative defense reactions of the host phagocytes (20). No conidial catalase has been identified previously in A. fumigatus. In Aspergillus nidulans, however, a...

Differentially expressed proteins of pathogenic Penicillium marneffei in yeast and mycelial phases

“…Differential expression levels of the other proteins identified in our study have not been reported previously. Catalase-peroxidase and isocitrate lyase have been reported to be related to pathogenicity in other fungi (Lorenz & Fink, 2001;Paris et al, 2003). Catalaseperoxidase shows bifunctional activity of both catalase and peroxidase to transform intracellular reactive oxygen species into harmless products in Aspergillus fumigatus and Aspergillus nidulans (Kawasaki & Aguirre, 2001; Paris et al, Table 2 and Fig.…”

Analysis of major intracellular proteins of Aspergillus fumigatus by MALDI mass spectrometry: Identification and characterisation of an elongation factor 1B protein with glutathione transferase activity

“…Dihydropteroate synthase (Afu3g07630) has been associated with drug resistance in Saccharomyces cerevisiae and has been shown to be derived from a polycistronic gene also responsible for the production of two other functional proteins [16]. Catalase 1 (Afu3g02270) involved in oxidative stress and identified here as three separate protein spots has been implicated in A. fumigatus pathogenicity [17]. Almost 44% (22/50) of all proteins identified were derived from intron-containing genes.…”

Fungal antioxidant pathways promote survival against neutrophils during infection

“…Further, we found that topical application of PX-12 was sufficient to restrict fungal growth in vivo, thereby indicating that this or similar compounds that target the thioredoxin pathway can block fungal thioredoxins and inhibit the predominant antioxidant defense utilized by these pathogens during infection. Figure 10 also illustrates that A. fumigatus produces 3 superoxide dismutases that catalyze the conversion of superoxide to H 2 O 2 (37,38). SOD1 and SOD3 are both cytoplasmic, whereas SOD2 is restricted to the mitochondrial membrane (37).…”

“…For example, A. fumigatus superoxide dismutases (SOD1/2/3) convert superoxide to the less-reactive hydrogen peroxide (37), whereas A. fumigatus catalases (CatA/1/2) convert hydrogen peroxide to H 2 O (38). In addition to ROS-catabolizing enzymes, filamentous fungi including A. fumigatus produce secondary metabolites such as gliotoxin and fumagillin, which inhibit NOX and are controlled by the master transcriptional regulator protein LaeA (39)(40)(41).…”