Proteome analysis of Aspergillus fumigatus identifies glycosylphosphatidylinositol-anchored proteins associated to the cell wall biosynthesis

Functional, transcriptomic, and lipidomic studies of the choC gene encoding a phospholipid methyltransferase in Aspergillus fumigatus

IMPORTANCE

This study explored the phospholipid metabolic pathway in A. fumigatus and its relationship with fungal growth, metabolism, and pathogenicity. ChoC, based on its critical roles in many aspects of the fungus and relatively conserved characteristics in filamentous fungi with low similarity with mammalian ones, can be a novel target of new antifungal drugs.

GPI-Anchored Protein Homolog IcFBR1 Functions Directly in Morphological Development of Isaria cicadae

Isaria cicadae is a famous edible and medicinal fungus in China and Asia. The molecular basis of morphogenesis and synnemal formation needs to be understood in more detail because this is the main source of biomass production in I. cicadae. In the present study, a fruiting body formation-related gene with a glycosylphosphatidylinositol (GPI) anchoring protein (GPI-Ap) gene homolog IcFBR1 was identified by screening random insertion mutants. Targeted deletion of IcFBR1 resulted in abnormal formation of synnemata, impairing aerial hyphae growth and sporulation. The IcFBR1 mutants were defective in the utilization of carbon sources with reduced polysaccharide contents and the regulation of amylase and protease activities. Transcriptome analysis of ΔIcfbr1 showed that IcFBR1 deletion influenced 49 gene ontology terms, including 23 biological processes, 9 molecular functions, and 14 cellular components. IcFBR1 is therefore necessary for regulating synnemal development, secondary metabolism, and nutrient utilization in this important edible and medicinal fungus. This is the first report illustrating that the function of IcFBR1 is associated with the synnemata in I. cicadae.

BsTup1 is required for growth, conidiogenesis, stress response and pathogenicity of Bipolaris sorokiniana

Tup1, a conserved transcriptional repressor, plays a critical role in the growth and development of fungi. Here, we identified a BsTup1 gene from the plant pathogenic fungus Bipolaris sorokiniana. The expression of BsTup1 showed a more than three-fold increase during the conidial stage compared with mycelium stage. Deletion of BsTup1 led to decrease hyphal growth and defect in conidia formation. A significant difference was detected in osmotic, oxidative, or cell wall stress responses between the WT and ΔBsTup1 strains. Pathogenicity assays showed that virulence of the ΔBsTup1 mutant was dramatically decreased on wheat and barely leaves. Moreover, it was observed that hyphal tips of the mutants could not form appressorium-like structures on the inner epidermis of onion and barley coleoptile. Yeast two-hybrid assays indicated that BsTup1 could interact with the BsSsn6. RNAseq revealed significant transcriptional changes in the ΔBsTup1 mutant with 2369 genes down-regulated and 2962 genes up-regulated. In these genes, we found that a subset of genes involved in fungal growth, sporulation, cell wall integrity, osmotic stress, oxidation stress, and pathogenicity, which were misregulated in the ΔBsTup1 mutant. These data revealed that BsTup1 has multiple functions in fungal growth, development, stress response and pathogenesis in B. sorokiniana.

Oryzapsins, the orthologs of yeast yapsin in Aspergillus oryzae, affect ergosterol synthesis

The oryzapsin genes opsA and opsB in Aspergillus oryzae encoding glycosylphosphatidylinositol (GPI)-anchored aspartic endopeptidase are homologs of Saccharomyces cerevisiae yapsins. We recently found another homolog, opsC, in the A. oryzae genome database, which was suggested to be a pseudogene. However, the profiles and roles of the proteins encoded by these genes have not yet been clarified. Toward this end, we first produced opsA- and opsB-overexpression strains and performed enzymatic analyses, revealing that OpsA and OpsB can attack sites other than the carboxyl-terminal peptide bonds of basic amino acids. Moreover, OpsA and OpsB were confirmed to bind to the cell membrane with a GPI anchor. Second, opsA and opsB single-deletion and double-deletion strains (ΔopsA, ΔopsB, and ΔopsAΔopsB) were constructed to explore the expected roles of oryzapsins in cell wall synthesis, similar to the role of yapsins. The transcription level of mpkA in the cell wall integrity pathway was increased in ΔopsB and ΔopsAΔopsB strains, suggesting that OpsB might be involved in processing cell wall synthesis-related proteins. Treatment with an ergosterol biosynthesis inhibitor reduced the growth of the ΔopsAΔopsB strain. Moreover, the mRNA levels of Aoerg1, Aoerg3-1, Aoerg3-2, Aoerg7b, Aoerg11, and Aohmg1,2 showed a decreasing tendency in the ΔopsAΔopsB strain, and the ergosterol content in the membrane was reduced in the ΔopsAΔopsB strain. These results suggest that oryzapsins exist in the cell membrane and play roles in the formation of cell membranes. This is the first report of the involvement of GPI-anchored aspartic endopeptidases in ergosterol biosynthesis.Key points• The oryzapsins have wider substrate specificity than yaspins in S. cerevisiae.• Unlike the yapsins, the oryzapsins might not be involved in the main structure synthesis of the cell wall.• The oryzapsins would be involved in ergosterol biosynthesis.

The Role of Melanin in the Biology and Ecology of Nematophagous Fungi

Melanin is a heteropolymer formed by the polymerization of phenolic and indolic compounds. It occurs in organisms across all biological kingdoms and has a range different of functions, thus indicating its important evolutionary role. The presence of melanin offers several protective advantages, including against ultraviolet radiation, traumatic damage, oxidative stress, extreme temperatures, and pressure. For many species of fungi, melanin also participates directly in the process of virulence and pathogenicity. These organisms can synthesize melanin in two main ways: using a substrate of endogenous origin, involving 1,8-dihydroxynaphthalene (DHN); alternatively, in an exogenous manner with the addition of L-3, 4-dihydroxyphenylalanine (L-DOPA or levodopa). As melanin is an amorphous and complex substance, its study requires expensive and inaccessible technologies and analyses are often difficult to perform with conventional biochemical techniques. As such, details about its chemical structure are not yet fully understood, particularly for nematophagous fungi that remain poorly studied. Thus, this review presents an overview of the different types of melanin, with an emphasis on fungi, and discusses the role of melanin in the biology and ecology of nematophagous fungi.

GPI Anchored Proteins in Aspergillus fumigatus and Cell Wall Morphogenesis

Glycosylphosphatidylinositol (GPI) anchored proteins are a class of proteins attached to the extracellular leaflet of the plasma membrane via a post-translational modification, the glycolipid anchor. GPI anchored proteins are expressed in all eukaryotes, from fungi to plants and animals. They display very diverse functions ranging from enzymatic activity, signaling, cell adhesion, cell wall metabolism, and immune response. In this review, we investigated for the first time an exhaustive list of all the GPI anchored proteins present in the Aspergillus fumigatus genome. An A. fumigatus mutant library of all the genes that encode in silico identified GPI anchored proteins has been constructed and the phenotypic analysis of all these mutants has been characterized including their growth, conidial viability or morphology, adhesion and the ability to form biofilms. We showed the presence of different fungal categories of GPI anchored proteins in the A. fumigatus genome associated to their role in cell wall remodeling, adhesion, and biofilm formation.

Cell wall polysaccharides from pathogenic fungi for diagnosis of fungal infectious disease

Invasive fungal diseases are associated with significant morbidity and mortality, particularly in immunocompromised individuals. Early and accurate diagnosis is crucial for effective treatment. Despite traditional methods such as microbiological culture, histopathology, radiology and direct microscopy are available, antigen/antibody-based diagnostics are emerging for diagnosis of invasive fungal infections (IFI). Fungal cell wall is a unique structure composed of polysaccharides that are well correlated with fungal burden during fungal infections. Based on this feature, cell wall polysaccharides have been explored as antigens in IFIs diagnostics such as the galactomannan assay, mannan test, β-glucan assay and cryptococcal CrAg test. Herein, we provide an overview on the cell wall polysaccharides from three opportunistic pathogens: Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans, and their applications for IFIs diagnosis. The clinical outcome of newly developed cell wall polysaccharides-based diagnostics is also discussed.

Glycobiology of Human Fungal Pathogens: New Avenues for Drug Development

Invasive fungal infections (IFI) are an increasing threat to the developing world, with fungal spores being ubiquitous and inhaled every day. Some fungal species are commensal organisms that are part of the normal human microbiota, and, as such, do not pose a threat to the immune system. However, when the natural balance of this association is disturbed or the host's immune system is compromised, these fungal pathogens overtake the organism, and cause IFI. To understand the invasiveness of these pathogens and to address the growing problem of IFI, it is essential to identify the cellular processes of the invading organism and their virulence. In this review, we will discuss the prevalence and current options available to treat IFI, including recent reports of drug resistance. Nevertheless, the main focus of this review is to describe the glycobiology of human fungal pathogens and how various components of the fungal cell wall, particularly cell wall polysaccharides and glycoconjugates, are involved in fungal pathogenicity, their biosynthesis and how they can be potentially exploited to develop novel antifungal treatment options. We will specifically describe the nucleotide sugar transporters (NSTs) that are important in fungal survival and suggest that the inhibition of fungal NSTs may potentially be useful to prevent the establishment of fungal infections.

Monoclonal Antibody AP3 Binds Galactomannan Antigens Displayed by the Pathogens Aspergillus flavus, A. fumigatus, and A. parasiticus

Aspergillus fumigatus and A. flavus are the fungal pathogens responsible for most cases of invasive aspergillosis (IA). Early detection of the circulating antigen galactomannan (GM) in serum allows the prompt application of effective antifungal therapy, thus improving the survival rate of IA patients. However, the use of monoclonal antibodies (mAbs) for the diagnosis of IA is often associated with false positives due to cross-reaction with bacterial polysaccharides. More specific antibodies are therefore needed. Here we describe the characterization of the Aspergillus-specific mAb AP3 (IgG1κ), including the precise identification of its corresponding antigen. The antibody was generated using A. parasiticus cell wall fragments and was shown to bind several Aspergillus species. Immunofluorescence microscopy revealed that AP3 binds a cell wall antigen, but immunoprecipitation and enzyme-linked immunosorbent assays showed that the antigen is also secreted into the culture medium. The inability of AP3 to bind the A. fumigatus galactofuranose (Galf )-deficient mutant ΔglfA confirmed that Galf residues are part of the epitope. Several lines of evidence strongly indicated that AP3 recognizes the Galf residues of O-linked glycans on Aspergillus proteins. Glycoarray analysis revealed that AP3 recognizes oligo-[β-D-Galf-1,5] sequences containing four or more residues with longer chains more efficiently. We also showed that AP3 captures GM in serum, suggesting it may be useful as a diagnostic tool for patients with IA.

The cell wall proteome from two strains of Pseudocercospora fijiensis with differences in virulence

Pseudocercospora fijiensis causes black Sigatoka disease, the most important threat to banana. The cell wall is crucial for fungal biological processes, including pathogenesis. Here, we performed cell wall proteomics analyses of two P. fijiensis strains, the highly virulent Oz2b, and the less virulent C1233 strains. Strains were starved from nitrogen to mimic the host environment. Interestingly, in vitro cultures of the C1233 strain grew faster than Oz2b in PDB medium, suggesting that C1233 survives outside the host better than the highly virulent Oz2b strain. Both strains were submitted to nitrogen starvation and the cell wall proteins were isolated and subjected to nano-HPLC-MS/MS. A total of 2686 proteins were obtained from which only 240 had a known function and thus, bioinformatics analyses were performed on this group. We found that 90 cell wall proteins were shared by both strains, 21 were unique for Oz2b and 39 for C1233. Shared proteins comprised 24 pathogenicity factors, including Avr4 and Ecp6, two effectors from P. fijiensis, while the unique proteins comprised 16 virulence factors in C1233 and 11 in Oz2b. The P. fijiensis cell wall proteome comprised canonical proteins, but thirty percent were atypical, a feature which in other phytopathogens has been interpreted as contamination. However, a comparison with the identities of atypical proteins in other reports suggests that the P. fijiensis proteins we detected were not contaminants. This is the first proteomics analysis of the P. fijiensis cell wall and our results expands the understanding of the fundamental biology of fungal phytopathogens and will help to decipher the molecular mechanisms of pathogenesis and virulence in P. fijiensis.

An Ssd1 Homolog Impacts Trehalose and Chitin Biosynthesis and Contributes to Virulence in Aspergillus fumigatus

Regulation of fungal cell wall biosynthesis is critical to maintain cell wall integrity in dynamic fungal infection microenvironments. Genes involved in this response that impact fungal fitness and host immune responses remain to be fully defined. In this study, we observed that a yeast ssd1 homolog, ssdA, in the filamentous fungus Aspergillus fumigatus is involved in trehalose and cell wall homeostasis. An ssdA null mutant strain exhibited an increase in trehalose levels and a reduction in fungal colony growth rate. In contrast, overexpression of ssdA perturbed trehalose biosynthesis and reduced germination of conidia. The ssdA null mutant strain was more resistant to cell wall-perturbing agents, while overexpression of ssdA increased sensitivity. Overexpression of ssdA significantly increased chitin levels, and both loss and overexpression of ssdA altered subcellular localization of the class V chitin synthase CsmA. Strikingly, overexpression of ssdA abolished adherence to abiotic surfaces and severely attenuated the virulence of A. fumigatus in a murine model of invasive pulmonary aspergillosis. Despite the severe in vitro fitness defects observed upon loss of ssdA, neither surface adherence nor murine survival was impacted. In conclusion, A. fumigatus SsdA plays a critical role in cell wall homeostasis impacting A. fumigatus-host interactions.IMPORTANCE The incidence of life-threatening infections caused by the filamentous fungus Aspergillus fumigatus is increasing along with an increase in the number of fungal strains resistant to contemporary antifungal therapies. The fungal cell wall and the associated carbohydrates required for its synthesis and maintenance are attractive drug targets given that many genes encoding proteins involved in cell wall biosynthesis and integrity are absent in humans. Importantly, genes and associated cell wall biosynthesis and homeostasis regulatory pathways remain to be fully defined in A. fumigatus In this report, we identify SsdA as an important component of trehalose and fungal cell wall biosynthesis in A. fumigatus that consequently impacts the host immune response and fungal virulence in animal models of infection.

Aspergillus-specific antibodies - Targets and applications

Aspergillus is a fungal genus comprising several hundred species, many of which can damage the health of plants, animals and humans by direct infection and/or due to the production of toxic secondary metabolites known as mycotoxins. Aspergillus-specific antibodies have been generated against polypeptides, polysaccharides and secondary metabolites found in the cell wall or secretions, and these can be used to detect and monitor infections or to quantify mycotoxin contamination in food and feed. However, most Aspergillus-specific antibodies are generated against heterogeneous antigen preparations and the specific target remains unknown. Target identification is important because this can help to characterize fungal morphology, confirm host penetration by opportunistic pathogens, detect specific disease-related biomarkers, identify new candidate targets for antifungal drug design, and qualify antibodies for diagnostic and therapeutic applications. In this review, we discuss how antibodies are raised against heterogeneous Aspergillus antigen preparations and how they can be characterized, focusing on strategies to identify their specific antigens and epitopes. We also discuss the therapeutic, diagnostic and biotechnological applications of Aspergillus-specific antibodies.

The roles of microsporidia spore wall proteins in the spore wall formation and polar tube anchorage to spore wall during development and infection processes

Microsporidia are highly specialized obligate intracellular, spore forming divergent fungi with a wide variety host range that includes most vertebrates and invertebrates. The resistant spores are surrounded by a rigid cell wall which consists of three layers: the electron-lucent chitin and protein inner endospore, the outer-electron-dense and mainly proteinaceous exospore and plasma membrane. Interestingly, microsporidia owns a special invasion organelle, called polar tube, coiled within the interior of the spore wall and attached to anchoring disk at the anterior end of spore. Spore wall and polar tube are the major apparatuses for mature spores adhering and infecting to the host cells. In this review, we summarize the research advances in spore wall proteins (SWPs) related to spore adherence and infection, and SWPs and deproteinated chitin spore coats (DCSCs) interaction associated with SWPs deposit processes and spore wall assembly. Furthermore, we highlight the SWPs-polar tube proteins (PTPs) interaction correlated to polar tube orderly orientation, arrangement and anchorage to anchoring disk. Based on results obtained, it is helpful to improve understanding of the spore wall assembly and polar tube orderly arrangement mechanisms and molecular pathogenesis of microsporidia infection. Also, such information will provide a basis for developing effective control strategies against microporidia.

Glycosylphosphatidylinositol Anchors from Galactomannan and GPI-Anchored Protein Are Synthesized by Distinct Pathways in Aspergillus fumigatus

Glycosylphosphatidylinositols (GPIs) are lipid anchors allowing the exposure of proteins at the outer layer of the plasma membrane. In fungi, a number of GPI-anchored proteins (GPI-APs) are involved in the remodeling of the cell wall polymers. GPIs follow a specific biosynthetic pathway in the endoplasmic reticulum. After the transfer of the protein onto the GPI-anchor, a lipid remodeling occurs to substitute the diacylglycerol moiety by a ceramide. In addition to GPI-APs, A. fumigatus produces a GPI-anchored polysaccharide, the galactomannan (GM), that remains unique in the fungal kingdom. To investigate the role of the GPI pathway in the biosynthesis of the GM and cell wall organization, the deletion of PER1-coding for a phospholipase required for the first step of the GPI lipid remodeling-was undertaken. Biochemical characterization of the GPI-anchor isolated from GPI-APs showed that the PER1 deficient mutant produced a lipid anchor with a diacylglycerol. The absence of a ceramide on GPI-anchors in the Δper1 mutant led to a mislocation of GPI-APs and to an alteration of the composition of the cell wall alkali-insoluble fraction. On the other hand, the GM isolated from the Δper1 mutant membranes possesses a ceramide moiety as the parental strain, showing that GPI anchor of the GM follow a distinct unknown biosynthetic pathway.

Aspergillus fumigatus morphology and dynamic host interactions

Aspergillus fumigatus is an environmental filamentous fungus that can cause life-threatening disease in immunocompromised individuals. The interactions between A. fumigatus and the host environment are dynamic and complex. The host immune system needs to recognize the distinct morphological forms of A. fumigatus to control fungal growth and prevent tissue invasion, whereas the fungus requires nutrients and needs to adapt to the hostile environment by escaping immune recognition and counteracting host responses. Understanding these highly dynamic interactions is necessary to fully understand the pathogenesis of aspergillosis and to facilitate the design of new therapeutics to overcome the morbidity and mortality caused by A. fumigatus. In this Review, we describe how A. fumigatus adapts to environmental change, the mechanisms of host defence, and our current knowledge of the interplay between the host immune response and the fungus.

Sphingolipids from the human fungal pathogen Aspergillus fumigatus

Sphingolipids (SPLs) are key components of the plasma membrane in yeast and filamentous fungi. These molecules are involved in a number of cellular processes, and particularly, SGLs are essential components of the highly polarized fungal growth where they are required for the formation of the polarisome organization at the hyphal apex. Aspergillus fumigatus, a human fungal pathogen, produce SGLs that are discriminated into neutral cerebrosides, glycosylinositolphosphoceramides (GIPCs) and glycosylphosphatidylinositol (GPI) anchors. In addition to complex hydrophilic head groups of GIPCs, A. fumigatus is, to date, the sole fungus that produces a GPI-anchored polysaccharide. These SPLs follow three different biosynthetic pathways. Genetics blockage leading to the inhibition of any SPL biosynthesis or to the alteration of the structure of SPL induces growth and virulence defects. The complete lipid moiety of SPLs is essential for the lipid microdomain organization and their biosynthetic pathways are potential antifungal targets but remains understudied.

Proteomics as a Tool to Identify New Targets Against Aspergillus and Scedosporium in the Context of Cystic Fibrosis

Cystic fibrosis (CF) is a genetic disorder that increases the risk of suffering microbial, including fungal, infections. In this paper, proteomics-based information was collated relating to secreted and cell wall proteins with potential medical applications from the most common filamentous fungi in CF, i.e., Aspergillus and Scedosporium/Lomentospora species. Among the Aspergillus fumigatus secreted allergens, β-1,3-endoglucanase, the alkaline protease 1 (Alp1/oryzin), Asp f 2, Asp f 13/15, chitinase, chitosanase, dipeptidyl-peptidase V (DppV), the metalloprotease Asp f 5, mitogillin/Asp f 1, and thioredoxin reductase receive a special mention. In addition, the antigens β-glucosidase 1, catalase, glucan endo-1,3-β-glucosidase EglC, β-1,3-glucanosyltransferases Gel1 and Gel2, and glutaminase A were also identified in secretomes of other Aspergillus species associated with CF: Aspergillus flavus, Aspergillus niger, Aspergillus nidulans, and Aspergillus terreus. Regarding cell wall proteins, cytochrome P450 and eEF-3 were proposed as diagnostic targets, and alkaline protease 2 (Alp2), Asp f 3 (putative peroxiredoxin pmp20), probable glycosidases Asp f 9/Crf1 and Crf2, GPI-anchored protein Ecm33, β-1,3-glucanosyltransferase Gel4, conidial hydrophobin Hyp1/RodA, and secreted aspartyl protease Pep2 as protective vaccines in A. fumigatus. On the other hand, for Scedosporium/Lomentospora species, the heat shock protein Hsp70 stands out as a relevant secreted and cell wall antigen. Additionally, the secreted aspartyl proteinase and an ortholog of Asp f 13, as well as the cell wall endo-1,3-β-D-glucosidase and 1,3-β-glucanosyl transferase, were also found to be significant proteins. In conclusion, proteins mentioned in this review may be promising candidates for developing innovative diagnostic and therapeutic tools for fungal infections in CF patients.

The Glycosylphosphatidylinositol Anchor Biosynthesis Genes GPI12, GAA1, and GPI8 Are Essential for Cell-Wall Integrity and Pathogenicity of the Maize Anthracnose Fungus Colletotrichum graminicola

Glycosylphosphatidylinositol (GPI) anchoring of proteins is one of the most common posttranslational modifications of proteins in eukaryotic cells and is important for associating proteins with the cell surface. In fungi, GPI-anchored proteins play essential roles in cross-linking of β-glucan cell-wall polymers and cell-wall rigidity. GPI-anchor synthesis is successively performed at the cytoplasmic and the luminal face of the ER membrane and involves approximately 25 proteins. While mutagenesis of auxiliary genes of this pathway suggested roles of GPI-anchored proteins in hyphal growth and virulence, essential genes of this pathway have not been characterized. Taking advantage of RNA interference (RNAi) we analyzed the function of the three essential genes GPI12, GAA1 and GPI8, encoding a cytoplasmic N-acetylglucosaminylphosphatidylinositol deacetylase, a metallo-peptide-synthetase and a cystein protease, the latter two representing catalytic components of the GPI transamidase complex. RNAi strains showed drastic cell-wall defects, resulting in exploding infection cells on the plant surface and severe distortion of in planta-differentiated infection hyphae, including formation of intrahyphal hyphae. Reduction of transcript abundance of the genes analyzed resulted in nonpathogenicity. We show here for the first time that the GPI synthesis genes GPI12, GAA1, and GPI8 are indispensable for vegetative development and pathogenicity of the causal agent of maize anthracnose, Colletotrichum graminicola.

Interference of Aspergillus fumigatus with the immune response

Aspergillus fumigatus is a saprotrophic filamentous fungus and also the most prevalent airborne fungal pathogen of humans. Depending on the host’s immune status, the variety of diseases caused by A. fumigatus ranges from allergies in immunocompetent hosts to life-threatening invasive infections in patients with impaired immunity. In contrast to the majority of other Aspergillus species, which are in most cases nonpathogenic, A. fumigatus features an armory of virulence determinants to establish an infection. For example, A. fumigatus is able to evade the human complement system by binding or degrading complement regulators. Furthermore, the fungus interferes with lung epithelial cells, alveolar macrophages, and neutrophil granulocytes to prevent killing by these immune cells. This chapter summarizes the different strategies of A. fumigatus to manipulate the immune response. We also discuss the potential impact of recent advances in immunoproteomics to improve diagnosis and therapy of an A. fumigatus infection.

Endoplasmic reticulum localized PerA is required for cell wall integrity, azole drug resistance, and virulence in Aspergillus fumigatus

GPI-anchoring is a universal and critical post-translational protein modification in eukaryotes. In fungi, many cell wall proteins are GPI-anchored, and disruption of GPI-anchored proteins impairs cell wall integrity. After being synthesized and attached to target proteins, GPI anchors undergo modification on lipid moieties. In spite of its importance for GPI-anchored protein functions, our current knowledge of GPI lipid remodelling in pathogenic fungi is limited. In this study, we characterized the role of a putative GPI lipid remodelling protein, designated PerA, in the human pathogenic fungus Aspergillus fumigatus. PerA localizes to the endoplasmic reticulum and loss of PerA leads to striking defects in cell wall integrity. A perA null mutant has decreased conidia production, increased susceptibility to triazole antifungal drugs, and is avirulent in a murine model of invasive pulmonary aspergillosis. Interestingly, loss of PerA increases exposure of β-glucan and chitin content on the hyphal cell surface, but diminished TNF production by bone marrow-derived macrophages relative to wild type. Given the structural specificity of fungal GPI-anchors, which is different from humans, understanding GPI lipid remodelling and PerA function in A. fumigatus is a promising research direction to uncover a new fungal specific antifungal drug target.

One single basic amino acid at the ω-1 or ω-2 site is a signal that retains glycosylphosphatidylinositol-anchored protein in the plasma membrane of Aspergillus fumigatus

Although the plasma membrane is the terminal destination for glycosylphosphatidylinositol (GPI) proteins in higher eukaryotes, cell wall-attached GPI proteins (GPI-CWPs) are found in many fungal species. In yeast, some of the cis-requirements directing localization of GPI proteins to the plasma membrane or cell wall are now understood. However, it remains to be determined how Aspergillus fumigatus, an opportunistic fungal pathogen, signals, and sorts GPI proteins to either the plasma membrane or the cell wall. In this study, chimeric green fluorescent proteins (GFPs) were constructed as fusions with putative C-terminal GPI signal sequences from A. fumigatus Mp1p, Gel1p, and Ecm33p, as well as site-directed mutations thereof. By analyzing cellular localization of chimeric GFPs using Western blotting, electron microscopy, and fluorescence microscopy, we showed that, in contrast to yeast, a single Lys residue at the ω-1 or ω-2 site alone could retain GPI-anchored GFP in the plasma membrane. Although the signal for cell wall distribution has not been identified yet, it appeared that the threonine/serine-rich region at the C-terminal half of AfMp1 was not required for cell wall distribution. Based on our results, the cis-requirements directing localization of GPI proteins in A. fumigatus are different from those in yeast.

Activity of native hydrolytic enzymes and their association with the cell wall of three ectomycorrhizal fungi

The ecological and biogeochemical relevance of hydrolytic enzymes associated with the fungal cell wall has been poorly studied in ectomycorrhizal (ECM) fungi. We used a modified sequential extraction procedure to investigate the activity of various hydrolytic enzymes (β-glucosidase, acid-phosphatase, leucine-aminopeptidase, chitinase, xylanase and glucuronidase) and their association with the cell wall of three ECM fungi (Rhizopogon roseolus, Paxillus involutus and Piloderma croceum). Fungi were grown on C-rich solid medium under three different P concentrations (3.7, 0.37 and 0.037 mM). The sequential extraction procedure classifies enzymes as: (a) cytosolic, (b) loosely bound, (c) hydrophobically bound, (d) ionically bound and (e) covalently bound. Results showed that for the same fungus absolute enzymatic activity was affected by P concentration, whilst enzymatic compartmentalization among the cytosol and the cell wall fractions was not. The association of enzymes with the cell wall was fungus- and enzyme-specific. Our data indicate also that enzymes best known for being either extracellular or cytosolic or both, do act in muro as well. The ecological implications of cell wall-bound enzymes and the potential applications and limitations of sequential extractions are further discussed.

Transcriptome and biochemical analysis reveals that suppression of GPI-anchor synthesis leads to autophagy and possible necroptosis in Aspergillus fumigatus

Previously, it has been shown that GPI proteins are required for cell wall synthesis and organization in Aspergillus fumigatus, a human opportunistic pathogen causing life-threatening invasive aspergillosis (IA) in immunocompromised patients. Blocking GPI anchor synthesis leads to severe phenotypes such as cell wall defects, increased cell death, and attenuated virulence. However, the mechanism by which these phenotypes are induced is unclear. To gain insight into global effects of GPI anchoring in A. fumigatus, in this study a conditional expression mutant was constructed and a genome wide transcriptome analysis was carried out. Our results suggested that suppression of GPI anchor synthesis mainly led to activation of phosphatidylinositol (PtdIns) signaling and ER stress. Biochemical and morphological evidence showed that autophagy was induced in response to suppression of the GPI anchor synthesis, and also an increased necroptosis was observed. Based on our results, we propose that activation of PtdIns3K and increased cytosolic Ca²⁺, which was induced by both ER stress and PtdIns signaling, acted as the main effectors to induce autophagy and possible necroptosis.

Fungal cell wall organization and biosynthesis

The composition and organization of the cell walls from Saccharomyces cerevisiae, Candida albicans, Aspergillus fumigatus, Schizosaccharomyces pombe, Neurospora crassa, and Cryptococcus neoformans are compared and contrasted. These cell walls contain chitin, chitosan, β-1,3-glucan, β-1,6-glucan, mixed β-1,3-/β-1,4-glucan, α-1,3-glucan, melanin, and glycoproteins as major constituents. A comparison of these cell walls shows that there is a great deal of variability in fungal cell wall composition and organization. However, in all cases, the cell wall components are cross-linked together to generate a cell wall matrix. The biosynthesis and properties of each of the major cell wall components are discussed. The chitin and glucans are synthesized and extruded into the cell wall space by plasma membrane-associated chitin synthases and glucan synthases. The glycoproteins are synthesized by ER-associated ribosomes and pass through the canonical secretory pathway. Over half of the major cell wall proteins are modified by the addition of a glycosylphosphatidylinositol anchor. The cell wall glycoproteins are also modified by the addition of O-linked oligosaccharides, and their N-linked oligosaccharides are extensively modified during their passage through the secretory pathway. These cell wall glycoprotein posttranslational modifications are essential for cross-linking the proteins into the cell wall matrix. Cross-linking the cell wall components together is essential for cell wall integrity. The activities of four groups of cross-linking enzymes are discussed. Cell wall proteins function as cross-linking enzymes, structural elements, adhesins, and environmental stress sensors and protect the cell from environmental changes.

A novel glycosylphosphatidylinositol-anchored glycoside hydrolase from Ustilago esculenta functions in β-1,3-glucan degradation

A glycoside hydrolase responsible for laminarin degradation was partially purified to homogeneity from a Ustilago esculenta culture filtrate by weak-cation-exchange, strong-cation-exchange, and size-exclusion chromatography. Three proteins in enzymatically active fractions were digested with chymotrypsin followed by liquid chromatography-tandem mass spectrometry (LC/MS/MS) analysis, resulting in the identification of three peptide sequences that shared significant similarity to a putative β-1,3-glucanase, a member of glucoside hydrolase family 16 (GH16) from Sporisorium reilianum SRZ2. A gene encoding a laminarin-degrading enzyme from U. esculenta, lam16A, was isolated by PCR using degenerate primers designed based on the S. reilianum SRZ2 β-1,3-glucanase gene. Lam16A possesses a GH16 catalytic domain with an N-terminal signal peptide and a C-terminal glycosylphosphatidylinositol (GPI) anchor peptide. Recombinant Lam16A fused to an N-terminal FLAG peptide (Lam16A-FLAG) overexpressed in Aspergillus oryzae exhibited hydrolytic activity toward β-1,3-glucan specifically and was localized both in the extracellular and in the membrane fractions but not in the cell wall fraction. Lam16A without a GPI anchor signal peptide was secreted extracellularly and was not detected in the membrane fraction. Membrane-anchored Lam16A-FLAG was released completely by treatment with phosphatidylinositol-specific phospholipase C. These results suggest that Lam16A is anchored in the plasma membrane in order to modify β-1,3-glucan associated with the inner cell wall and that Lam16A is also used for the catabolism of β-1,3-glucan after its release in the extracellular medium.

The functions of grainy head-like proteins in animals and fungi and the evolution of apical extracellular barriers

The Grainy head (GRH) family of transcription factors are crucial for the development and repair of epidermal barriers in all animals in which they have been studied. This is a high-level functional conservation, as the known structural and enzymatic genes regulated by GRH proteins differ between species depending on the type of epidermal barrier being formed. Interestingly, members of the CP2 superfamily of transcription factors, which encompasses the GRH and LSF families in animals, are also found in fungi--organisms that lack epidermal tissues. To shed light on CP2 protein function in fungi, we characterized a Neurospora crassa mutant lacking the CP2 member we refer to as grainy head-like (grhl). We show that Neurospora GRHL has a DNA-binding specificity similar to that of animal GRH proteins and dissimilar to that of animal LSF proteins. Neurospora grhl mutants are defective in conidial-spore dispersal due to an inability to remodel the cell wall, and we show that grhl mutants and the long-known conidial separation-2 (csp-2) mutants are allelic. We then characterized the transcriptomes of both Neurospora grhl mutants and Drosophila grh mutant embryos to look for similarities in the affected genes. Neurospora grhl appears to play a role in the development and remodeling of the cell wall, as well as in the activation of genes involved in defense and virulence. Drosophila GRH is required to activate the expression of many genes involved in cuticular/epidermal-barrier formation. We also present evidence that GRH plays a role in adult antimicrobial defense. These results, along with previous studies of animal GRH proteins, suggest the fascinating possibility that the apical extracellular barriers of some animals and fungi might share an evolutionary connection, and that the formation of physical barriers in the last common ancestor was under the control of a transcriptional code that included GRH-like proteins.

Identification and proteomic analysis of a novel gossypol-degrading fungal strain

BACKGROUND

Cottonseed meal, an important source of feed raw materials, has limited use in the feed industry because of the presence of the highly toxic gossypol. The aim of the current work was to isolate the gossypol-degrading fungus from a soil microcosm and investigate the proteins involved in gossypol degradation.

RESULTS

A fungal strain, AN-1, that uses gossypol as its sole carbon source was isolated and identified as Aspergillus niger. A large number of intracellular proteins were detected using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but no significant difference was observed between the glucose-containing and gossypol-containing mycelium extracts. Two-dimensional gel electrophoresis results showed that the protein spots were concentrated in the 25.0-66.2 kDa range and distributed in different pI gradients. PDQuest software showed that 51 protein spots in the gels were differentially expressed. Of these, 20 differential protein spots, including six special spots expressed in gossypol, were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

CONCLUSION

The fungus AN-1 biodegraded gossypol and the proteomic analysis results indicate that some proteins were involved in the gossypol biodegradation during fungus survival, using gossypol as its sole carbon source.

Protein Glycosylation in Aspergillus fumigatus Is Essential for Cell Wall Synthesis and Serves as a Promising Model of Multicellular Eukaryotic Development

Glycosylation is a conserved posttranslational modification that is found in all eukaryotes, which helps generate proteins with multiple functions. Our knowledge of glycosylation mainly comes from the investigation of the yeast Saccharomyces cerevisiae and mammalian cells. However, during the last decade, glycosylation in the human pathogenic mold Aspergillus fumigatus has drawn significant attention. It has been revealed that glycosylation in A. fumigatus is crucial for its growth, cell wall synthesis, and development and that the process is more complicated than that found in the budding yeast S. cerevisiae. The present paper implies that the investigation of glycosylation in A. fumigatus is not only vital for elucidating the mechanism of fungal cell wall synthesis, which will benefit the design of new antifungal therapies, but also helps to understand the role of protein glycosylation in the development of multicellular eukaryotes. This paper describes the advances in functional analysis of protein glycosylation in A. fumigatus.

Annexin C4 in A. fumigatus: a proteomics approach to understand the function

Annexin C4 has been identified as a new member of fungal annexin family. In search of function, we have generated an annexin C4 disruptant strain of human pathogen, Aspergillus fumigatus. Detailed phenotypic analysis confirmed a non essential role of annexin C4 in the growth and sporulation of this pathogen. We applied a comparative proteomics strategy to understand the possible role of this protein in the fungus. The modification of respiratory chain proteins and stress response proteins suggests the occurrence of a mild oxidative stress in anxC4 disruptant strain. This may indicate a possible anti stress function of annexin C4 in A. fumigatus.

Identification of virulence determinants of the human pathogenic fungi Aspergillus fumigatus and Candida albicans by proteomics

Both fungi Candida albicans and Aspergillus fumigatus can cause a number of life-threatening systemic infections in humans. The commensal yeast C. albicans is one of the main causes of nosocomial fungal infectious diseases, whereas the filamentous fungus A. fumigatus has become one of the most prevalent airborne fungal pathogens. Early diagnosis of these fungal infections is challenging, only a limited number of antifungals for treatment are available, and the molecular details of pathogenicity are hardly understood. The completion of both the A. fumigatus and C. albicans genome sequence provides the opportunity to improve diagnosis, to define new drug targets, to understand the functions of many uncharacterised proteins, and to study protein regulation on a global scale. With the application of proteomic tools, particularly two-dimensional gel electrophoresis and LC/MS-based methods, a comprehensive overview about the proteins of A. fumigatus and C. albicans present or induced during environmental changes and stress conditions has been obtained in the past 5 years. However, for the discovery of further putative virulence determinants, more sensitive and targeted proteomic methods have to be applied. Here, we review the recent proteome data generated for A. fumigatus and C. albicans that are related to factors required for pathogenicity.

Proteome profiling and functional classification of intracellular proteins from conidia of the human-pathogenic mold Aspergillus fumigatus

Aspergillus fumigatus is a ubiquitously distributed filamentous fungus that has emerged as one of the most serious life-threatening pathogens in immunocompromised patients. The mechanisms for its pathogenicity are poorly understood. Here, we analyzed the proteome of dormant A. fumigatus conidia as the fungal entity having the initial contact with the host. Applying two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), we established a 2-D reference map of conidial proteins. By MALDI-TOF mass spectrometry, we identified a total number of 449 different proteins. We show that 57 proteins of our map are over-represented in resting conidia compared to mycelium. Enzymes involved in reactive oxygen intermediates (ROI) detoxification, pigment biosynthesis, and conidial rodlet layer formation were highly abundant in A. fumigatus spores and most probably account for their enormous stress resistance. Interestingly, pyruvate decarboxylase and alcohol dehydrogenase were detectable in dormant conidia, suggesting that alcoholic fermentation plays a role during dormancy or early germination. Moreover, we show that enzymes for rapid reactivation of protein biosynthesis and metabolic processes are preserved in resting conidia, which therefore feature the potential to immediately respond to an environmental stimulus by germination. The generated data lay the foundations for further proteomic analyses and a better understanding of fungal pathogenesis.

Analysis of the cellular Aspergillus fumigatus proteome that reacts with sera from rabbits developing an acquired immunity after experimental aspergillosis

Invasive aspergillosis caused by the mould Aspergillus fumigatus is a life-threatening lung or systemic infection in the immunocompromised host. In this study, a protective immune response against the disease was achieved in two infected rabbits, and the cellular fungal antigenic proteome that mediated such a response was investigated against the background of vaccine development efforts. Altogether, 59 different Aspergillus proteins were found becoming reactive in the course of the developing immunity, many of which are described in this context for the first time. These included proteins related to oxidative stress management, glycolysis and other metabolic pathways. As oxidative stress is suspected to be one of the major defense mechanisms, the results may indicate at least in part a continuous response of the pathogen to evade the host's immune system. In addition, proteins with suspected cell surface association or crucial function for fungal cell development were identified. As these antigens are newly recognized during the process of the developing immunoprotection, they may not only represent valuable infection markers but also importantly broaden the list of possible vaccine candidates.

Proteomics of plant pathogenic fungi

Plant pathogenic fungi cause important yield losses in crops. In order to develop efficient and environmental friendly crop protection strategies, molecular studies of the fungal biological cycle, virulence factors, and interaction with its host are necessary. For that reason, several approaches have been performed using both classical genetic, cell biology, and biochemistry and the modern, holistic, and high-throughput, omic techniques. This work briefly overviews the tools available for studying Plant Pathogenic Fungi and is amply focused on MS-based Proteomics analysis, based on original papers published up to December 2009. At a methodological level, different steps in a proteomic workflow experiment are discussed. Separate sections are devoted to fungal descriptive (intracellular, subcellular, extracellular) and differential expression proteomics and interactomics. From the work published we can conclude that Proteomics, in combination with other techniques, constitutes a powerful tool for providing important information about pathogenicity and virulence factors, thus opening up new possibilities for crop disease diagnosis and crop protection.

Proteome analysis of Aspergillus fumigatus total membrane proteins identifies proteins associated with the glycoconjugates and cell wall biosynthesis using 2D LC-MS/MS

We attempted to identify membrane proteins associated with the glycoconjugates and cell wall biosynthesis in the total membrane preparations of Aspergillus fumigatus. The total membrane preparations were first run on 1D gels, and then the stained gels were cut and submitted to in-gel digestion followed by 2D LC-MS/MS and database search. A total of 530 proteins were identified with at least two peptides detected with MS/MS spectra. Seventeen integral membrane proteins were involved in N-, O-glycosylation or GPI anchor biosynthesis. Nine membrane proteins were involved in cell wall biosynthesis. Eight proteins were identified as enzymes involved in sphingolipid synthesis. In addition, the proteins involved in cell wall and ergosterol biosynthesis can potentially be used as antifungal drug targets. Our method, for the first time, clearly provided a global view of the membrane proteins associated with glycoconjugates and cell wall biosynthesis in the total membrane proteome of A. fumigatus.

An approach to characterize the membrane proteome of Candida albicans

Evaluation of: Cabezon V, Llama-Palacios A, Nombela C, Monteoliva L, Gil C: Analysis of Candida albicans plasma membrane proteome. Proteomics 9, 4770–4786 (2009). The opportunistic human fungal pathogen Candida albicans causes a wide variety of infections, including deep systemic infection. The C. albicans plasma membrane is an important interface in the host–pathogen relationship. Plasma membrane proteins mediate a variety of functions, including sensing and signaling to the external environment, in which the glycosylphosphatidylinositol (GPI)-anchored membrane proteins play a crucial role. A subproteomic approach to obtain a global picture of the protein composition of the C. albicans plasma membrane was developed, and different strategies were tested in order to extract the largest number of yeast plasma membrane proteins and GPI-anchored membrane proteins. These methods involved protoplast generation, mechanical disruption, ultracentrifugation in sucrose gradients and Na2CO3 treatments. To isolate GPI-anchored proteins two additional steps were performed: two-phase separation and phosphatidylinositol-phospholipase C treatment. After liquid chromatography tandem mass spectrometry analysis using both a MALDI-TOF/TOF and a linear ion trap quadrupole, a total of 214 membrane proteins were identified, including 41 already described as plasma membrane proteins, 20 plasma membrane-associated proteins and 22 proteins with unknown membrane localization. Bioinformatic analysis revealed that this set of C. albicans membrane proteins is highly enriched in proteins involved in biopolymer biosynthesis or transport processes. Furthermore, following phosphatidylinositol-phospholipase C treatment, 12 GPI-anchored membrane proteins were released and identified; most of them are associated with cell wall glucan synthesis and maintenance or are virulence factors, such as phospholipases or aspartyl proteinases.

A monoclonal IgM directed against immunodominant catalase B of cell wall of Aspergillus fumigatus exerts anti-A. fumigatus activities

Aspergillus fumigatus, a ubiquitous fungus, has been reported to cause human diseases like allergic pulmonary aspergillosis, aspergilloma and invasive infection. Limited spectrum and emergence of resistance has become a serious problem with available antifungals. Therefore, an alternative approach is required for successful treatment of mycoses. In the present study, immunogenic protein profile of A. fumigatus cell wall was generated using two-dimensional-gel electrophoresis and three hybridomas producing monoclonal antibodies (MAbs; IgM) were selected after fusion experiments. Of these three MAbs, MAb-7 exhibited potent in vitro inhibitory activity, which was confirmed by MTT assay, fluorescence-activated cell sorter analysis and immuno-fluorescence studies, and the protein was identified as catalase B using MALDI-TOF-MS.

Characterization of the Aspergillus fumigatus phosphomannose isomerase Pmi1 and its impact on cell wall synthesis and morphogenesis

Phosphomannose isomerase (PMI) is an enzyme catalysing the interconversion of mannose 6-phosphate (Man-6-P) and fructose 6-phosphate (Fru-6-P). The reaction catalysed by PMI is the first committed step in the synthesis of mannose-containing sugar chains and provides a link between glucose metabolism and mannosylation. In this study, the pmi1 gene was identified to encode PMI in the human fungal pathogen Aspergillus fumigatus. Characterization of A. fumigatus Pmi1 expressed in Escherichia coli revealed that this PMI mainly catalysed the conversion of Fru-6-P to Man-6-P and that its binding affinity for Man-6-P was similar to that of yeast PMIs, but different to those of PMIs from bacteria or animals. Loss of pmi1 was lethal unless Man was provided in the growth medium. However, a Δpmi1 mutant cell showed a significantly reduced growth rate at a high concentration of Man. Biochemical analysis revealed that both inadequate and replete Man led to an accumulation of intracellular Man-6-P and a reduction in the amount of α-glucan in the cell wall. Uncoupling of the link between energy production and glycosylation by deletion of the pmi1 gene led to phenotypes such as defects in cell wall integrity, abnormal morphology and reduced conidiation. Our results reveal that PMI activity is essential for viability and plays a central regulatory role in both cell wall synthesis and energy production in A. fumigatus.

Identification of a putative Crf splice variant and generation of recombinant antibodies for the specific detection of Aspergillus fumigatus

BACKGROUND

Aspergillus fumigatus is a common airborne fungal pathogen for humans. It frequently causes an invasive aspergillosis (IA) in immunocompromised patients with poor prognosis. Potent antifungal drugs are very expensive and cause serious adverse effects. Their correct application requires an early and specific diagnosis of IA, which is still not properly achievable. This work aims to a specific detection of A. fumigatus by immunofluorescence and the generation of recombinant antibodies for the detection of A. fumigatus by ELISA.

RESULTS

The A. fumigatus antigen Crf2 was isolated from a human patient with proven IA. It is a novel variant of a group of surface proteins (Crf1, Asp f9, Asp f16) which belong to the glycosylhydrolase family. Single chain fragment variables (scFvs) were obtained by phage display from a human naive antibody gene library and an immune antibody gene library generated from a macaque immunized with recombinant Crf2. Two different selection strategies were performed and shown to influence the selection of scFvs recognizing the Crf2 antigen in its native conformation. Using these antibodies, Crf2 was localized in growing hyphae of A. fumigatus but not in spores. In addition, the antibodies allowed differentiation between A. fumigatus and related Aspergillus species or Candida albicans by immunofluorescence microscopy. The scFv antibody clones were further characterized for their affinity, the nature of their epitope, their serum stability and their detection limit of Crf2 in human serum.

CONCLUSION

Crf2 and the corresponding recombinant antibodies offer a novel approach for the early diagnostics of IA caused by A. fumigatus.

Comparative proteomic analysis of an Aspergillus fumigatus mutant deficient in glucosidase I (AfCwh41)

Alpha-glucosidase I regulates trimming of the terminal alpha-1,2-glucose residue in the N-glycan processing pathway, which plays an important role in quality control systems in mammalian cells. Previously, we identified the gene encoding alpha-glucosidase I in the opportunistic human fungal pathogen Aspergillus fumigatus, namely Afcwh41. Deletion of the Afcwh41 gene results in a severe reduction of conidia formation, a temperature-sensitive deficiency of cell wall integrity, and abnormalities of polar growth and septation. An upregulation of the genes encoding Rho-type GTPases was also observed, which suggests activation of the cell wall integrity pathway in the mutant. Using 2D gel analysis, we revealed that the proteins involved in protein assembly, ubiquitin-mediated degradation and actin organization are altered in the DeltaAfcwh41 mutant. Evidence was obtained for a defect in the polarized localization of the actin cytoskeleton in the mutant. Our results suggest that blocking of the glucose trimming in A. fumigatus might induce accumulation of misfolded proteins in the endoplasmic reticulum; these misfolded proteins are probably required for cell wall synthesis and thus activate the cell wall integrity pathway, which then causes the abnormal polarity associated with the DeltaAfcwh41 mutant.

Proteome analysis for pathogenicity and new diagnostic markers for Aspergillus fumigatus

With the completion of the Aspergillus fumigatus genome it is now possible to study protein regulation on a global scale. One of the most suitable protein separation techniques is based on 2D-gel electrophoresis, which allows the separation of proteins based on their charge and size in a gel matrix. In addition, gel-free proteomics techniques based on liquid-chromatography coupled with mass spectrometry have gained importance. With the application of proteomic tools a comprehensive overview about the proteins of A. fumigatus present or induced during environmental changes and stress conditions can be obtained. For A. fumigatus, several proteomic studies have already been published including the response of the fungus to oxidative stress that induced the up-regulation of many proteins including catalases and thioredoxin peroxidase. Since many of the identified proteins/genes were apparently regulated by a putative Saccharomyces cerevisiae Yap1 homolog, the corresponding gene of A. fumigatus was identified, designated Afyap1 and further characterized. In addition, some of the gene products expressed under stress conditions are also known fungal antigens, such as the thioredoxin peroxidase AspF3. Thus, besides pathogenicity studies, proteomics also delivers the tools to screen for new antigens which could improve the diagnosis of diseases caused by A. fumigatus.