The mitA gene of Aspergillus fumigatus is required for mannosylation of inositol-phosphorylceramide, but is dispensable for pathogenicity

Discovery of α-(1→6)-linked mannan structures resembling yeast N-glycan outer chains in Aspergillus fumigatus mycelium

The cellular surface of the pathogenic filamentous fungus Aspergillus fumigatus is enveloped in a mannose layer, featuring well-established fungal-type galactomannan and O-mannose-type galactomannan. This study reports the discovery of cell wall component in A. fumigatus mycelium, which resembles N-glycan outer chains found in yeast. The glycosyltransferases involved in its biosynthesis in A. fumigatus were identified, with a focus on two key α-(1→2)-mannosyltransferases, Mnn2 and Mnn5, and two α-(1→6)-mannosyltransferases, Mnn9 and Van1. In vitro examination revealed the roles of recombinant Mnn2 and Mnn5 in transferring α-(1→2)-mannosyl residues. Proton nuclear magnetic resonance (1H-NMR) analysis of cell wall extracts from the ∆mnn2∆mnn5 strain indicated the existence of an α-(1→6)-linked mannan backbone in the A. fumigatus mycelium, with Mnn2 and Mnn5 adding α-(1→2)-mannosyl residues to this backbone. The α-(1→6)-linked mannan backbone was absent in strains where mnn9 or van1 was disrupted in the parental ∆mnn2∆mnn5 strain in A. fumigatus. Mnn9 and Van1 functioned as α-(1→6)-linked mannan polymerases in heterodimers when co-expressed in Escherichia coli, indicating their crucial role in biosynthesizing the α-(1→6)-linked mannan backbone. Disruptions of these mannosyltransferases did not affect fungal-type galactomannan biosynthesis. This study provides insights into the complexity of fungal cell wall architecture and a better understanding of mannan biosynthesis in A. fumigatus.

IMPORTANCE

This study unravels the complexities of mannan biosynthesis in A. fumigatus, a key area for antifungal drug discovery. It reveals the presence of α-(1→6)-linked mannan structures resembling yeast N-glycan outer chains in A. fumigatus mycelium, offering fresh insights into the fungal cell wall's design. Key enzymes, Mnn2, Mnn5, Mnn9, and Van1, are instrumental in this process, with Mnn2 and Mnn5 adding specific mannose residues and Mnn9 and Van1 assembling the α-(1→6)-linked mannan structures. Although fungal-type galactomannan's presence in the cell wall is known, the existence of an α-(1→6)-linked mannan adds a new dimension to our understanding. This intricate web of mannan biosynthesis opens avenues for further exploration and enhances our understanding of fungal cell wall dynamics, paving the way for targeted drug development.

Genetic Characterization of the Acidic and Neutral Glycosphingolipid Biosynthetic Pathways in Neurospora crassa

Fungal glycosphingolipids (GSLs) are important membrane components which play a key role in vesicle trafficking. To assess the importance of GSLs in the fungal life cycle, we performed a mutant phenotypic study of the acidic and neutral GSL biosynthetic pathways in Neurospora crassa. GSL biosynthesis begins with two reactions leading up to the formation of dihydrosphingosine. The first of these reactions is catalyzed by serine palmitoyltransferase and generates 3-keto dihydrosphinganine. In N. crassa, this reaction is catalyzed by GSL-1 and GSL-2 and is required for viability. The second reaction is carried out by GSL-3, a 3-keto dihydrosphinoganine reductase to generate dihydrosphingosine, which is used for the synthesis of neutral and acidic GSLs. We found that deletion mutations in the acidic GSL pathway leading up to the formation of mannosylinositol-phosphoceramide are lethal, indicating that acidic GSLs are essential for viability in N. crassa. Once mannosylinositol-phosphoceramide is made, it is further modified by GSL-5, an inositol-phosphoceramide-B C26 hydroxylase, which adds a hydroxyl group to the amide-linked fatty acid. GSL-5 is not required for viability but gives a clear mutant phenotype affecting all stages of the life cycle. Our results show that the synthesis of mannosylinositol-phosphoceramide is required for viability and that the modification of the amide-linked fatty acid is important for acidic GSL functionality. We also examined the neutral GSL biosynthetic pathway and identified the presence of glucosylceramide. The deletion of neutral GSL biosynthetic genes affected hyphal morphology, vegetative growth rate, conidiation, and female development. Our results indicate that the synthesis of neutral GSLs is essential for normal growth and development of N. crassa.

Characterisation of a gene cluster involved in aspergillus fumigatus zwitterionic glycosphingolipid synthesis

The human pathogenic fungus Aspergillus fumigatus synthesises the zwitterionic glycolipid Manα1,3Manα1,6GlcNα1,2IPC, named Af3c. Similar glycosphingolipids having a glucosamine (GlcN) linked in α1,2 to inositolphosphoceramide (IPC) as core structure have only been described in a few pathogenic fungi. Here, we describe an Ammophilus fumigatus cluster of 5 genes (AFUA_8G02040 to AFUA_8G02090) encoding proteins required for the glycan part of the glycosphingolipid Af3c. Besides the already characterised UDP-GlcNAc:IPC α1,2-N-acetylglucosaminyltransferase (GntA), the cluster encodes a putative UDP-GlcNAc transporter (NstA), a GlcNAc de-N-acetylase (GdaA), and two mannosyltransferases (OchC and ClpC). The function of these proteins was inferred from analysis of the glycolipids extracted from A. fumigatus strains deficient in one of the genes. Moreover, successive introduction of the genes encoding GntA, GdaA, OchC and ClpC in the yeast Saccharomyces cerevisiae enabled the reconstitution of the Af3c biosynthetic pathway. Absence of Af3c slightly reduced the virulence of A. fumigatus in a Galleria mellonella infection model.

Glycosphingolipids in Filamentous Fungi: Biological Roles and Potential Applications in Cosmetics and Health Foods

Filamentous fungi are a group of economically important fungi used in the production of fermented foods, industrial enzymes, and secondary metabolites. Glycosphingolipids (GSLs) as constituents of lipid rafts are involved in growth, differentiation, and response to environment stress in filamentous fungi. In addition to these key roles, GSLs are also important in the barrier function of skin to retain moisture as a moisturizing ingredient in cosmetics or health products for their strong biological activity as a functional component. GSLs found in filamentous fungi are divided in two major classes: neutral GSLs (glycosylceramides), glucosylceramides (GlcCers), and/or galactosylceramides (GalCers) and acidic GSLs, mannosylinositol phosphorylceramide (MIPC) and mannosyldiinositol phosphorylceramide [M(IP)₂C]. Glycosylceramides are one of the abundant GSLs in Aspergillus and known to improve skin-barrier function and prevent intestinal impairment as a prebiotic. Some filamentous fungi of Aspergillus spp., synthesizing both GlcCer and GalCer, would be an amenable source to exploit glycosylceramides that wildly adding in cosmetics as moisturizing ingredients or health food as dietary supplements. In this minireview, the types, structures, and biosynthetic pathways of GSLs in filamentous fungi, and the relevance of GSLs in fungal growth, spore formation, and environmental stress response are explained. Furthermore, the advantage, potential development, and application of GlcCer and GalCer from filamentous fungi Aspergillus spp. are also investigate based on the use of plant GlcCer in health foods and cosmetics.

Galactomannan Produced by Aspergillus fumigatus: An Update on the Structure, Biosynthesis and Biological Functions of an Emblematic Fungal Biomarker

The galactomannan (GM) that is produced by the human fungal pathogen Aspergillus fumigatus is an emblematic biomarker in medical mycology. The GM is composed of two monosaccharides: mannose and galactofuranose. The furanic configuration of galactose residues, absent in mammals, is responsible for the antigenicity of the GM and has favoured the development of ELISA tests to diagnose aspergillosis in immunocompromised patients. The GM that is produced by A. fumigatus is a unique fungal polysaccharide containing a tetramannoside repeat unit and having three different forms: (i) membrane bound through a glycosylphosphatidylinositol (GPI)-anchor, (ii) covalently linked to β-1,3-glucans in the cell wall, or (iii) released in the culture medium as a free polymer. Recent studies have revealed the crucial role of the GM during vegetative and polarized fungal growth. This review highlights these recent data on its biosynthetic pathway and its biological functions during the saprophytic and pathogenic life of this opportunistic human fungal pathogen.

Fungal sphingolipids: role in the regulation of virulence and potential as targets for future antifungal therapies

INTRODUCTION

The antifungal therapy currently available includes three major classes of drugs: polyenes, azoles and echinocandins. However, the clinical use of these compounds faces several challenges: while polyenes are toxic to the host, antifungal resistance to azoles and echinocandins has been reported.

AREAS COVERED

Fungal sphingolipids (SL) play a pivotal role in growth, morphogenesis and virulence. In addition, fungi possess unique enzymes involved in SL synthesis, leading to the production of lipids which are absent or differ structurally from the mammalian counterparts. In this review, we address the enzymatic reactions involved in the SL synthesis and their relevance to the fungal pathogenesis, highlighting their potential as targets for novel drugs and the inhibitors described so far.

EXPERT OPINION

The pharmacological inhibition of fungal serine palmitoyltransferase depends on the development of specific drugs, as myriocin also targets the mammalian enzyme. Inhibitors of ceramide synthase might constitute potent antifungals, by depleting the pool of complex SL and leading to the accumulation of the toxic intermediates. Acylhydrazones and aureobasidin A, which inhibit GlcCer and IPC synthesis, are not toxic to the host and effectively treat invasive mycoses, emerging as promising new classes of antifungal drugs.

Biosynthesis of β-(1→5)-Galactofuranosyl Chains of Fungal-Type and O-Mannose-Type Galactomannans within the Invasive Pathogen Aspergillus fumigatus

β-(1→5)-Galactofuranosyl residues are widely distributed in the subphylum Pezizomycotina of the phylum Ascomycota. Pezizomycotina includes many plant and animal pathogens. Although the structure of β-(1→5)-galactofuranosyl residues of galactomannans in filamentous fungi was discovered long ago, it remains unclear which enzyme is responsible for biosynthesis of this glycan. Fungal cell wall formation processes are complicated, and information concerning glycosyltransferases is essential for understanding them. In this study, we showed that GfsA and GfsC are responsible for the biosynthesis of all β-(1→5)-galactofuranosyl residues of fungal-type and O-mannose-type galactomannans. The data presented here indicate that β-(1→5)-galactofuranosyl residues are involved in cell growth, conidiation, polarity, and cell surface hydrophobicity. Our new understanding of β-(1→5)-galactofuranosyl residue biosynthesis provides important novel insights into the formation of the complex cell wall structure and the virulence of the members of the subphylum Pezizomycotina.

The pathogenic fungus Aspergillus fumigatus contains galactomannans localized on the surface layer of its cell walls, which are involved in various biological processes. Galactomannans comprise α-(1→2)-/α-(1→6)-mannan and β-(1→5)-/β-(1→6)-galactofuranosyl chains. We previously revealed that GfsA is a β-galactofuranoside β-(1→5)-galactofuranosyltransferase involved in the biosynthesis of β-(1→5)-galactofuranosyl chains. In this study, we clarified the biosynthesis of β-(1→5)-galactofuranosyl chains in A. fumigatus. Two paralogs exist within A. fumigatus: GfsB and GfsC. We show that GfsB and GfsC, in addition to GfsA, are β-galactofuranoside β-(1→5)-galactofuranosyltransferases by biochemical and genetic analyses. GfsA, GfsB, and GfsC can synthesize β-(1→5)-galactofuranosyl oligomers at up to lengths of 7, 3, and 5 galactofuranoses within an established in vitro highly efficient assay of galactofuranosyltransferase activity. Structural analyses of galactomannans extracted from ΔgfsB, ΔgfsC, ΔgfsAC, and ΔgfsABC strains revealed that GfsA and GfsC synthesized all β-(1→5)-galactofuranosyl residues of fungal-type and O-mannose-type galactomannans and that GfsB exhibited limited function in A. fumigatus. The loss of β-(1→5)-galactofuranosyl residues decreased the hyphal growth rate and conidium formation ability and increased the abnormal hyphal branching structure and cell surface hydrophobicity, but this loss is dispensable for sensitivity to antifungal agents and virulence toward immunocompromised mice.

IMPORTANCE β-(1→5)-Galactofuranosyl residues are widely distributed in the subphylum Pezizomycotina of the phylum Ascomycota. Pezizomycotina includes many plant and animal pathogens. Although the structure of β-(1→5)-galactofuranosyl residues of galactomannans in filamentous fungi was discovered long ago, it remains unclear which enzyme is responsible for biosynthesis of this glycan. Fungal cell wall formation processes are complicated, and information concerning glycosyltransferases is essential for understanding them. In this study, we showed that GfsA and GfsC are responsible for the biosynthesis of all β-(1→5)-galactofuranosyl residues of fungal-type and O-mannose-type galactomannans. The data presented here indicate that β-(1→5)-galactofuranosyl residues are involved in cell growth, conidiation, polarity, and cell surface hydrophobicity. Our new understanding of β-(1→5)-galactofuranosyl residue biosynthesis provides important novel insights into the formation of the complex cell wall structure and the virulence of the members of the subphylum Pezizomycotina.

Overview of the Interplay Between Cell Wall Integrity Signaling Pathways and Membrane Lipid Biosynthesis in Fungi: Perspectives for Aspergillus fumigatus

The cell wall (CW) and plasma membrane are fundamental structures that define cell shape and support different cellular functions. In pathogenic fungi, such as Aspegillus fumigatus, they not only play structural roles but are also important for virulence and immune recognition. Both the CW and the plasma membrane remain as attractive drug targets to treat fungal infections, such as the Invasive Pulmonary Aspergillosis (IPA), a disease associated with high morbimortality in immunocompromised individuals. The low efficiency of echinocandins that target the fungal CW biosynthesis, the occurrence of environmental isolates resistant to azoles such as voriconazole and the known drawbacks associated with amphotericin toxicity foster the urgent need for fungal-specific drugable targets and/or more efficient combinatorial therapeutic strategies. Reverse genetic approaches in fungi unveil that perturbations of the CW also render cells with increased susceptibility to membrane disrupting agents and vice-versa. However, how the fungal cells simultaneously cope with perturbation in CW polysaccharides and cell membrane proteins to allow morphogenesis is scarcely known. Here, we focus on current information on how the main signaling pathways that maintain fungal cell wall integrity, such as the Cell Wall Integrity and the High Osmolarity Glycerol pathways, in different species often cross-talk to regulate the synthesis of molecules that comprise the plasma membrane, especially sphingolipids, ergosterol and phospholipids to promote functioning of both structures concomitantly and thus, cell viability. We propose that the conclusions drawn from other organisms are the foundations to point out experimental lines that can be endeavored in A. fumigatus.

Biological Roles Played by Sphingolipids in Dimorphic and Filamentous Fungi

Filamentous and dimorphic fungi cause invasive mycoses associated with high mortality rates. Among the fungal determinants involved in the establishment of infection, glycosphingolipids (GSLs) have gained increased interest in the last few decades. GSLs are ubiquitous membrane components that have been isolated from both filamentous and dimorphic species and play a crucial role in polarized growth as well as hypha-to-yeast transition. In fungi, two major classes of GSLs are found: neutral and acidic GSLs. Neutral GSLs comprise glucosylceramide and galactosylceramide, which utilize Δ4-Δ8-9-methyl-sphingadienine as a sphingoid base, linked to a C_16-18 fatty acid chain, forming ceramide, and to a sugar residue, such as glucose or galactose. In contrast, acidic GSLs include glycosylinositol phosphorylceramides (GIPCs), composed of phytosphingosine attached to a long or very long fatty acid chain (C_18-26) and to diverse and complex glycan groups via an inositol-phosphate linker. GIPCs are absent in mammalian cells, while fungal glucosylceramide and galactosylceramide are present but diverge structurally from their counterparts. Therefore, these compounds and their biosynthetic pathways represent potential targets for the development of selective therapeutic strategies. In this minireview, we discuss the enzymatic steps involved in the production of fungal GSLs, analyze their structure, and address the role of the currently characterized genes in the biology and pathogenesis of filamentous and dimorphic fungi.

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.

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.

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Sphingolipidomics: An Important Mechanistic Tool for Studying Fungal Pathogens

Sphingolipids form of a unique and complex group of bioactive lipids in fungi. Structurally, sphingolipids of fungi are quite diverse with unique differences in the sphingoid backbone, amide linked fatty acyl chain and the polar head group. Two of the most studied and conserved sphingolipid classes in fungi are the glucosyl- or galactosyl-ceramides and the phosphorylinositol containing phytoceramides. Comprehensive structural characterization and quantification of these lipids is largely based on advanced analytical mass spectrometry based lipidomic methods. While separation of complex lipid mixtures is achieved through high performance liquid chromatography, the soft - electrospray ionization tandem mass spectrometry allows a high sensitivity and selectivity of detection. Herein, we present an overview of lipid extraction, chromatographic separation and mass spectrometry employed in qualitative and quantitative sphingolipidomics in fungi.

Characterization of an N-acetylglucosaminyltransferase involved in Aspergillus fumigatus zwitterionic glycoinositolphosphoceramide biosynthesis

Glycoinositolphosphoceramides (GIPCs) are complex sphingolipids present at the plasma membrane of various eukaryotes with the important exception of mammals. In fungi, these glycosphingolipids commonly contain an α-mannose residue (Man) linked at position 2 of the inositol. However, several pathogenic fungi additionally synthesize zwitterionic GIPCs carrying an α-glucosamine residue (GlcN) at this position. In the human pathogen Aspergillus fumigatus, the GlcNα1,2IPC core (where IPC is inositolphosphoceramide) is elongated to Manα1,3Manα1,6GlcNα1,2IPC, which is the most abundant GIPC synthesized by this fungus. In this study, we identified an A. fumigatus N-acetylglucosaminyltransferase, named GntA, and demonstrate its involvement in the initiation of zwitterionic GIPC biosynthesis. Targeted deletion of the gene encoding GntA in A. fumigatus resulted in complete absence of zwitterionic GIPC; a phenotype that could be reverted by episomal expression of GntA in the mutant. The N-acetylhexosaminyltransferase activity of GntA was substantiated by production of N-acetylhexosamine-IPC in the yeast Saccharomyces cerevisiae upon GntA expression. Using an in vitro assay, GntA was furthermore shown to use UDP-N-acetylglucosamine as donor substrate to generate a glycolipid product resistant to saponification and to digestion by phosphatidylinositol-phospholipase C as expected for GlcNAcα1,2IPC. Finally, as the enzymes involved in mannosylation of IPC, GntA was localized to the Golgi apparatus, the site of IPC synthesis.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Deletion of PdMit1, a homolog of yeast Csg1, affects growth and Ca(2+) sensitivity of the fungus Penicillium digitatum, but does not alter virulence

GDP-mannose:inositol-phosphorylceramide (MIPC) and its derivatives are important for Ca(2+) sensitization of Saccharomyces cerevisiae and for the virulence of Candida albicans, but its role in the virulence of plant fungal pathogens remains unclear. In this study, we report the identification and functional characterization of PdMit1, the gene encoding MIPC synthase in Penicillium digitatum, one of the most important pathogens of postharvest citrus fruits. To understand the function of PdMit1, a PdMit1 deletion mutant was generated. Compared to its wild-type control, the PdMit1 deletion mutant exhibited slow radial growth, decreased conidia production and delayed conidial germination, suggesting that PdMit1 is important for the growth of mycelium, sporulation and conidial germination. The PdMit1 deletion mutant also showed hypersensitivity to Ca(2+). Treatment with 250 mmol/l Ca(2+) induced vacuole fusion in the wild-type strain, but not in the PdMit1 deletion mutant. Treatment with 250mmol/lCaCl2 upregulated three Ca(2+)-ATPase genes in the wild-type strain, and this was significantly inhibited in the PdMit1 deletion mutant. These results suggest that PdMit1 may have a role in regulating vacuole fusion and expression of Ca(2+)-ATPase genes by controlling biosynthesis of MIPC, and thereby imparts P. digitatum Ca(2+) tolerance. However, we found that PdMit1 is dispensable for virulence of P. digitatum.

Biosynthesis of the fungal cell wall polysaccharide galactomannan requires intraluminal GDP-mannose

Fungal cell walls frequently contain a polymer of mannose and galactose called galactomannan. In the pathogenic filamentous fungus Aspergillus fumigatus, this polysaccharide is made of a linear mannan backbone with side chains of galactofuran and is anchored to the plasma membrane via a glycosylphosphatidylinositol or is covalently linked to the cell wall. To date, the biosynthesis and significance of this polysaccharide are unknown. The present data demonstrate that deletion of the Golgi UDP-galactofuranose transporter GlfB or the GDP-mannose transporter GmtA leads to the absence of galactofuran or galactomannan, respectively. This indicates that the biosynthesis of galactomannan probably occurs in the lumen of the Golgi apparatus and thus contrasts with the biosynthesis of other fungal cell wall polysaccharides studied to date that takes place at the plasma membrane. Transglycosylation of galactomannan from the membrane to the cell wall is hypothesized because both the cell wall-bound and membrane-bound polysaccharide forms are affected in the generated mutants. Considering the severe growth defect of the A. fumigatus GmtA-deficient mutant, proving this paradigm might provide new targets for antifungal therapy.

Fast preparation of fungal DNA for PCR screening

Rapid DNA preparation for the quick screening is highly demanded in diverse research fields. Here, we combined an extraction buffer and heat treatment to generate DNA templates from yeast and filamentous fungal materials for PCR. This method may be widely applicable to diverse fungal species in clinical and basic studies.

Approaching the secrets of N-glycosylation in Aspergillus fumigatus: characterization of the AfOch1 protein

The mannosyltransferase Och1 is the key enzyme for synthesis of elaborated protein N-glycans in yeast. In filamentous fungi genes implicated in outer chain formation are present, but their function is unclear. In this study we have analyzed the Och1 protein of Aspergillus fumigatus. We provide first evidence that poly-mannosylated N-glycans exist in A. fumigatus and that their synthesis requires AfOch1 activity. This implies that AfOch1 plays a similar role as S. cerevisiae ScOch1 in the initiation of an N-glycan outer chain. A Δafoch1 mutant showed normal growth under standard and various stress conditions including elevated temperature, cell wall and oxidative stress. However, sporulation of this mutant was dramatically reduced in the presence of high calcium concentrations, suggesting that certain proteins engaged in sporulation require N-glycan outer chains to be fully functional. A characteristic feature of AfOch1 and Och1 homologues from other filamentous fungi is a signal peptide that clearly distinguishes them from their yeast counterparts. However, this difference does not appear to have consequences for its localization in the Golgi. Replacing the signal peptide of AfOch1 by a membrane anchor had no impact on its ability to complement the sporulation defect of the Δafoch1 strain. The mutant triggered a normal cytokine response in infected murine macrophages, arguing against a role of outer chains as relevant Aspergillus pathogen associated molecular patterns. Infection experiments provided no evidence for attenuation in virulence; in fact, according to our data the Δafoch1 mutant may even be slightly more virulent than the control strains.

Aspergillus fumigatus: contours of an opportunistic human pathogen

Aspergillus fumigatus is currently the major air-borne fungal pathogen. It is able to cause several forms of disease in humans of which invasive aspergillosis is the most severe. The high mortality rate of this disease prompts increased efforts to disclose the basic principles of A. fumigatus pathogenicity. According to our current knowledge, A. fumigatus lacks sophisticated virulence traits; it is nevertheless able to establish infection due to its robustness and ability to adapt to a wide range of environmental conditions. This review focuses on two crucial aspects of invasive aspergillosis: (i) properties of A. fumigatus that are relevant during infection and may distinguish it from non-pathogenic Aspergillus species and (ii) interactions of the pathogen with the innate and adaptive immune systems.