Variability of Aspergillus nidulans antigens with media and time and temperature of growth

Standardization and characterization of antigens for the diagnosis of aspergillosis

The aim of this study was to develop and characterize antigens for the diagnosis of aspergillosis. Nine strains of Aspergillus species Aspergillus fumigatus , Aspergillus flavus , and Aspergillus niger were grown in Sabouraud and Smith broth to produce exoantigens. The antigens were tested by immunodiffusion against sera from patients with aspergillosis and other systemic mycoses. The protein fraction of the antigens was detected by SDS–PAGE; Western blot and representative bands were assessed by mass spectrometry coupled to a nano Acquity UltraPerformance LC and analyzed by the Mascot search engine. Concurrently, all sera were tested with Platelia Aspergillus EIA. The most reactive antigens to sera from patients infected by A. fumigatus were produced by A. fumigatus MG2 Sabouraud and pooled A. fumigatus Sabouraud samples, both with a sensitivity of 93% and specificity of 100% and 97%, respectively. Aspergillus niger and A. flavus antigens were reactive against A. niger and A. flavus sera, each one with a sensitivity and specificity of 100%. Two proteins, probably responsible for antigenic activity, β-glucosidase in A. fumigatus and α-amylase in A. niger were attained. The commercial kit had a specificity of 22%, sensitivity of 100%, positive predictive value of 48%, and negative predictive value of 100%. The antigens produced showed high sensitivity and specificity and can be exploited for diagnostics of aspergilloma.

Effect of culture temperature on the heterologous expression of Pleurotus eryngii versatile peroxidase in Aspergillus hosts

Production of recombinant versatile peroxidase in Aspergillus hosts was optimized through the modification of temperature during bioreactor cultivations. To further this purpose, the cDNA encoding a versatile peroxidase of Pleurotus eryngii was expressed under control of the alcohol dehydrogenase (alcA) promoter of Aspergillus nidulans. A dependence of recombinant peroxidase production on cultivation temperature was found. Lowering the culture temperature from 28 to 19 degrees C enhanced the level of active peroxidase 5.8-fold and reduced the effective proteolytic activity twofold. Thus, a maximum peroxidase activity of 466 U L(-1) was reached. The same optimization scheme was applied to a recombinant Aspergillus niger that bore the alcohol dehydrogenase regulator (alcR), enabling transformation with the peroxidase cDNA under the same alcA promoter. However, with this strain, the peroxidase activity was not improved, while the effective proteolytic activity was increased between 3- and 11-fold compared to that obtained with A. nidulans.

The zrfA and zrfB genes of Aspergillus fumigatus encode the zinc transporter proteins of a zinc uptake system induced in an acid, zinc-depleted environment

Zinc is an essential micronutrient that cells must obtain from the environment in order to develop their normal growth. Previous work performed at our laboratory showed that the synthesis of immunodominant antigens from Aspergillus spp., including A. fumigatus, was up-regulated by a low environmental concentration of zinc. These results suggested that a tightly regulated system for the fungus to grow under zinc-limiting conditions must underlie the ability of A. fumigatus to acquire zinc in such environments. In this work, we show that zrfA and zrfB are two of the genes that encode membrane zinc transporters from A. fumigatus in this system. Expression of these genes is differentially down-regulated by increasing concentrations of zinc in the medium. Thus, the transcription of zrfB is turned off at a concentration 50-fold higher than that for zrfA transcription. In addition, phenotypic analyses of single zrfADelta and zrfBDelta mutants and a double zrfAzrfBDelta mutant revealed that the deletion of zrfB causes a greater defect in growth than the single deletion of zrfA. Deletion of both genes has a dramatic effect on growth under acid, zinc-limiting conditions. Interestingly, in neutral or slightly alkaline zinc-depleted medium, the transcriptional expression of both genes is down-regulated to such an extent that even in the absence of a supplement of zinc, the expression of zrfA and zrfB is strongly reduced. This fact correlates with the growth observed in alkaline medium, in which even a zrfAzrfBDelta double mutant was able to grow in a similar way to the wild-type under extremely zinc-limiting conditions. In sum, the zinc transport proteins encoded by zrfA and zrfB are members of a zinc uptake system of A. fumigatus that operates mainly under acid, zinc-limiting conditions.

Production of culture filtrates of Sporothrix schenckii in diverse culture media

Mycelial-form Sporothrix schenckii was studied to determine if growth in complex (Sabouraud-dextrose) or defined culture media (minimal medium, Gibco Medium 199 with and without Hepes buffer) with differing initial pH levels would affect expression of antigen components. Cultures were evaluated by continuous monitoring and serial sampling for various parameters. Great variation was seen in the protein and antigenic patterns induced by the different media. The expression of a 55 kDa component accompanied by significant acidification of the culture medium at the beginning of the stationary growth phase was notable in Sabouraud medium. In the chemically defined media, a 90 kDa component was expressed that reacted with sera from patients with sporotrichosis. The pH in these media showed little change during the different growth phases of the fungus. Among the media studied, minimal medium favored the expression of the greatest number of antigenic components. In all of the assays, the stationary growth phase appeared to be optimal for content of antigenic components. Cross reactions were not observed with any of the culture filtrates using sera from patients with other mycoses.

Distinctive properties of the catalase B of Aspergillus nidulans

Aspergillus nidulans catalase B (CatB) was purified to homogeneity and characterized as a hydroperoxidase which resembles typical catalases in some physicochemical characteristics: (1) it has an apparent molecular weight of 360000 and is composed of four glycosylated subunits, (2) it has hydrophobic properties as revealed by extractability in ethanol/chloroform and binding to phenyl-Superose, and (3) it has an acidic isoelectric point at pH 3. 5. Also CatB exhibits some distinctive properties, e.g. it is not inhibited by the presence of 2% sodium dodecyl sulfate, 9 M urea or reducing agents. Furthermore, even though CatB does not exhibit any residual peroxidase activity, it is able to retain up to 38% of its initial catalase activity after incubation with the typical catalase inhibitor 3-amino-1,2,4-triazole.

Zinc-regulated biosynthesis of immunodominant antigens from Aspergillus spp

ASPND1 and ASPF2 are immunodominant antigens from Aspergillus nidulans and A. fumigatus, respectively, that are readily synthesized in infections in the human host, as demonstrated by their reactivity with more than 80% of sera from patients with aspergilloma or allergic bronchopulmonary aspergillosis. We demonstrate here that both antigens are exclusively produced under situations of low bioavailability of free Zn2+. Addition of micromolar concentrations of Zn2+ to the culture medium strongly stimulated Aspergillus growth but totally inhibited ASPND1 or ASPF2 production. This effect was specific, since other divalent metals had no effect. Removal of endogenous Zn2+ by a chelator also stimulated ASPND1 production, and the effect was specifically reversed by Zn2+. These results suggest a possible role of these antigens in the survival of the fungus in the lungs.

Immunological characterization of Asp f 2, a major allergen from Aspergillus fumigatus associated with allergic bronchopulmonary aspergillosis

The 37-kDa recombinant protein Asp f 2, encoding an allergen of Aspergillus fumigatus, was expressed in a prokaryotic expression system and immunologically evaluated for its functional and structural properties. The open reading frame for a 310-amino-acid-long protein was shown to encode a signal peptide of 31 amino acids. A native 37-kDa culture filtrate protein and a 55-kDa mycelial glycoprotein (gp55) exhibited complete N-terminal sequence homology to Asp f 2. A GenBank search for homologous proteins revealed 60 and 44% sequence homologies to the cytosolic protein ASPND1 from Aspergillus nidulans and fibrinogen binding protein from Candida albicans, respectively. The glycosylation sites and cysteine molecules are conserved in all the three proteins. The extracellular matrix protein laminin showed a dose-dependent interaction with Asp f 2. This protein, expressed as a major cell-associated protein within 24 h of in vitro fungal culture, comprises 20 to 40% of total fungal protein. Furthermore, both native and recombinant Asp f 2 exhibited specific immunoglobulin (IgE) binding with allergic bronchopulmonary aspergillosis (ABPA) and cystic fibrosis-ABPA patients, whereas A. fumigatus-sensitized allergic asthma and normal control subjects failed to show IgE binding with Asp f 2. These results indicate that Asp f 2 is a major allergen of A. fumigatus exhibiting IgE antibody binding with sera from patients with ABPA. The antigen should be explored further for its potential role in the differential diagnosis of A. fumigatus-associated allergic diseases.

The recombinant antigen ASPND1r from Aspergillus nidulans is specifically recognized by sera from patients with aspergilloma

A 996 bp Aspergillus nidulans cDNA encoding the ASPND1 immunodominant antigen was cloned and expressed in Escherichia coli as a fusion protein with the enzyme glutathione S-transferase (GST) from Schistosoma japonicum. The GST-ASPND1 fusion protein was purified from isolated bacterial inclusion bodies by preparative SDS-PAGE. After cleavage with thrombin, the ASPND1 recombinant antigen (ASPND1r) and the GST protein were separated by SDS-PAGE and immunoblotted with a number of different human sera. The sera from 22 (88%) of 25 patients with an aspergilloma recognized the ASPND1r recombinant antigen on immunoblots. Forty-nine normal human sera and 14 sera from patients with other infections were unreactive. The ASPND1r expressed in E. coli could therefore be used, in combination with previously reported recombinant antigens, as a standardized antigen for serological and clinical diagnosis of Aspergillus-associated diseases.

Characterization of the Aspergillus nidulans aspnd1 gene demonstrates that the ASPND1 antigen, which it encodes, and several Aspergillus fumigatus immunodominant antigens belong to the same family

For the first time, an immunodominant Aspergillus nidulans antigen (ASPND1) consistently reactive with serum samples from aspergilloma patients has been purified and characterized, and its coding gene (aspnd1) has been cloned and sequenced. ASPND1 is a glycoprotein with four N-glycosidically-bound sugar chains (around 2.1 kDa each) which are not necessary for reactivity with immune human sera. The polypeptide part is synthesized as a 277-amino-acid precursor of 30.6 kDa that after cleavage of a putative signal peptide of 16 amino acids, affords a mature protein of 261 amino acids with a molecular mass of 29 kDa and a pI of 4.24 (as deduced from the sequence). The ASPND1 protein is 53.1% identical to the AspfII allergen from Aspergillus fumigatus and 48% identical to an unpublished Candida albicans antigen. All of the cysteine residues and most of the glycosylation sites are perfectly conserved in the three proteins, suggesting a similar but yet unknown function. Analysis of the primary structure of the ASPND1 coding gene (aspnd1) has allowed the establishment of a clear relationship between several previously reported A. fumigatus and A. nidulans immunodominant antigens.

Immunoblotting patterns in the serodiagnosis of aspergilloma: antibody response to the 90kDa Aspergillus fumigatus antigen

At present there are no accepted criteria to assess the usefulness of Western blot assays for the serodiagnosis of aspergilloma. An Aspergillus fumigatus cytosolic fraction complex (CFC) composed of four proteins (p90, p60, p40, and p37) has been identified. The usefulness of Western blotting with CFC antigens for the serodiagnosis of aspergilloma was evaluated in 25 patients with well-established diagnoses and in 94 controls. The most consistently reactive antigen was p90 (92% of patients with aspergilloma), followed by p40 (76%) and the entire CFC taken together (76%). With these data, interpretive criteria for positive and negative immunoblots were established, with p90 indicated as a helpful marker of aspergilloma.

An immunodominant 90-kilodalton Aspergillus fumigatus antigen is the subunit of a catalase

We have identified, purified, and characterized structurally and functionally a 90-kDa immunodominant antigen associated with the water-soluble fraction of Aspergillus fumigatus. This antigen is recognized by 90.3% of serum samples from patients with aspergilloma and should be considered either by itself or better in combination with other purified antigens as a candidate for developing a standardized immunoassay for the detection of aspergilloma. p90 is a glycoprotein containing at least two two N-linked sugar chains of 2 and 5 kDa, respectively, which are not necessary for its reactivity with aspergilloma serum samples. Using specific anti-p90 rabbit serum, we have demonstrated that under native conditions, p90 exists in oligomeric form and has associated catalase activity. This activity is resistant to extreme temperatures (> 60 degrees C), reducing agents (40 mM dithiothreitol), high concentrations of denaturing agents such as 8 M urea and 8% sodium dodecyl sulfate, and treatments with ethanol-chloroform-water (5:3:10 [vol/vol]) mixtures.