Dataset Information

Conidial hydrophobins of Aspergillus fumigatus.

ABSTRACT: The surface of Aspergillus fumigatus conidia, the first structure recognized by the host immune system, is covered by rodlets. We report that this outer cell wall layer contains two hydrophobins, RodAp and RodBp, which are found as highly insoluble complexes. The RODA gene was previously characterized, and DeltarodA conidia do not display a rodlet layer (N. Thau, M. Monod, B. Crestani, C. Rolland, G. Tronchin, J. P. Latgé, and S. Paris, Infect. Immun. 62:4380-4388, 1994). The RODB gene was cloned and disrupted. RodBp was highly homologous to RodAp and different from DewAp of A. nidulans. DeltarodB conidia had a rodlet layer similar to that of the wild-type conidia. Therefore, unlike RodAp, RodBp is not required for rodlet formation. The surface of DeltarodA conidia is granular; in contrast, an amorphous layer is present at the surface of the conidia of the DeltarodA DeltarodB double mutant. These data show that RodBp plays a role in the structure of the conidial cell wall. Moreover, rodletless mutants are more sensitive to killing by alveolar macrophages, suggesting that RodAp or the rodlet structure is involved in the resistance to host cells.

SUBMITTER: Paris S

PROVIDER: S-EPMC150101 | biostudies-literature | 2003 Mar

REPOSITORIES: biostudies-literature

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Conidial hydrophobins of Aspergillus fumigatus.

Paris Sophie S Debeaupuis Jean-Paul JP Crameri Reto R Carey Marilyn M Charlès Franck F Prévost Marie Christine MC Schmitt Christine C Philippe Bruno B Latgé Jean Paul JP

Applied and environmental microbiology 20030301 3

The surface of Aspergillus fumigatus conidia, the first structure recognized by the host immune system, is covered by rodlets. We report that this outer cell wall layer contains two hydrophobins, RodAp and RodBp, which are found as highly insoluble complexes. The RODA gene was previously characterized, and DeltarodA conidia do not display a rodlet layer (N. Thau, M. Monod, B. Crestani, C. Rolland, G. Tronchin, J. P. Latgé, and S. Paris, Infect. Immun. 62:4380-4388, 1994). The RODB gene was clone ...[more]

PMID: 12620846

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Project description:Aerial conidia of Ascomycetes and Basidiomycetes are coated with an amphipathic hydrophobin layer commonly called rodlet layer, that renders their surface hydrophobic and resist wetting, thus facilitating effective dispersal in the air. Fungal hydrophobins are small secreted proteins with specific hydropathy patterns and eight cysteine residues ordered in a particular manner which define the two well characterized classes I and II of hydrophobins and a third intermediate class (Kershaw and Talbot, 1998. Littlejohn et al, 2012; Jensen et al, 2010). Wessels 1994). Class I assemblies are generally water insoluble, have an amyloid structure and form the patterned rodlet layer. Class II are smaller proteins than class I and are soluble in aqueous ethanol mixtures of SDS. The intermediate class is a rather heterogenous tote class which would gather non-class I and non-class II hydrophobins without a defined structure. In addition to the role of the rodlet in the fungal life during conidiogenesis and conidial dispersal in the air, it was shown that rodlets can have a role in fungal – host interactions and favour the pathogenic behavior of the fungal pathogens in humans, plant and insect hosts (Talbot et al., 1996, Aimanianda et al, 2009; Zhang et al, 2011). In Aspergillusfumigatus rodlets immunosilence the conidium and their loss from the conidial surface initiates the host immune response (Aimanianda et al., 2009). Our study is focused on the Rod A protein which forms the rodlet structure on the surface of the conidium of A. fumigatus. In spite of their prominent morphological and biological role, the molecular basis for rodlet self-assembly and desagregation in this fungal species has not been understood yet. Point mutations in the rodA gene have helped understanding the mechanism which drives hydrophobin proteins to assemble into highly ordered structures anchored to the conidium surface. Moreover, the biochemical events responsible for the lysis of the rodlets have been investigated.

Project description:Aspergillus fumigatus, a filamentous fungus producing bluish-green conidia, is an important opportunistic pathogen that primarily affects immunocompromised patients. Conidial pigmentation of A. fumigatus significantly influences its virulence in a murine model. In the present study, six genes, forming a gene cluster spanning 19 kb, were identified as involved in conidial pigment biosynthesis in A. fumigatus. Northern blot analyses showed the six genes to be developmentally regulated and expressed during conidiation. The gene products of alb1 (for "albino 1"), arp1 (for "aspergillus reddish-pink 1"), and arp2 have high similarity to polyketide synthases, scytalone dehydratases, and hydroxynaphthalene reductases, respectively, found in the dihydroxynaphthalene (DHN)-melanin pathway of brown and black fungi. The abr1 gene (for "aspergillus brown 1") encodes a putative protein possessing two signatures of multicopper oxidases. The abr2 gene product has homology to the laccase encoded by the yA gene of Aspergillus nidulans. The function of ayg1 (for "aspergillus yellowish-green 1") remains unknown. Involvement of the six genes in conidial pigmentation was confirmed by the altered conidial color phenotypes that resulted from disruption of each gene in A. fumigatus. The presence of a DHN-melanin pathway in A. fumigatus was supported by the accumulation of scytalone and flaviolin in the arp1 deletant, whereas only flaviolin was accumulated in the arp2 deletants. Scytalone and flaviolin are well-known signature metabolites of the DHN-melanin pathway. Based on DNA sequence similarity, gene disruption results, and biochemical analyses, we conclude that the 19-kb DNA fragment contains a six-gene cluster which is required for conidial pigment biosynthesis in A. fumigatus. However, the presence of abr1, abr2, and ayg1 in addition to alb1, arp1, and arp2 suggests that conidial pigment biosynthesis in A. fumigatus is more complex than the known DHN-melanin pathway.

Project description:BACKGROUND:The pathogenic mold Aspergillus fumigatus is the most frequent infectious cause of death in severely immunocompromised individuals such as leukemia and bone marrow transplant patients. Germination of inhaled conidia (asexual spores) in the host is critical for the initiation of infection, but little is known about the underlying mechanisms of this process. RESULTS:To gain insights into early germination events and facilitate the identification of potential stage-specific biomarkers and vaccine candidates, we have used quantitative shotgun proteomics to elucidate patterns of protein abundance changes during early fungal development. Four different stages were examined: dormant conidia, isotropically expanding conidia, hyphae in which germ tube emergence has just begun, and pre-septation hyphae. To enrich for glycan-linked cell wall proteins we used an alkaline cell extraction method. Shotgun proteomic resulted in the identification of 375 unique gene products with high confidence, with no evidence for enrichment of cell wall-immobilized and secreted proteins. The most interesting discovery was the identification of 52 proteins enriched in dormant conidia including 28 proteins that have never been detected in the A. fumigatus conidial proteome such as signaling protein Pil1, chaperones BipA and calnexin, and transcription factor HapB. Additionally we found many small, Aspergillus specific proteins of unknown function including 17 hypothetical proteins. Thus, the most abundant protein, Grg1 (AFUA_5G14210), was also one of the smallest proteins detected in this study (M.W. 7,367). Among previously characterized proteins were melanin pigment and pseurotin A biosynthesis enzymes, histones H3 and H4.1, and other proteins involved in conidiation and response to oxidative or hypoxic stress. In contrast, expanding conidia, hyphae with early germ tubes, and pre-septation hyphae samples were enriched for proteins responsible for housekeeping functions, particularly translation, respiratory metabolism, amino acid and carbohydrate biosynthesis, and the tricarboxylic acid cycle. CONCLUSIONS:The observed temporal expression patterns suggest that the A. fumigatus conidia are dominated by small, lineage-specific proteins. Some of them may play key roles in host-pathogen interactions, signal transduction during conidial germination, or survival in hostile environments.

Dataset Information

Conidial hydrophobins of Aspergillus fumigatus.

Publications

Conidial hydrophobins of Aspergillus fumigatus.

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