Abstract
Resistance of Aspergillus fumigatus conidia to desiccation and their capacity to reach the alveoli are partly due to the presence of a hydrophobic layer composed of a protein from the hydrophobin family, called RodA, which covers the conidial surface. In A. fumigatus there are seven hydrophobins (RodA–RodG) belonging to class I and III. Most of them have never been studied. We constructed single and multiple hydrophobin-deletion mutants until the generation of a hydrophobin-free mutant. The phenotype, immunogenicity, and virulence of the mutants were studied. RODA is the most expressed hydrophobin in sporulating cultures, whereas RODB is upregulated in biofilm conditions and in vivo Only RodA, however, is responsible for rodlet formation, sporulation, conidial hydrophobicity, resistance to physical insult or anionic dyes, and immunological inertia of the conidia. None of the hydrophobin plays a role in biofilm formation or its hydrophobicity. RodA is the only needed hydrophobin in A. fumigatus, conditioning the structure, permeability, hydrophobicity, and immune-inertia of the cell wall surface in conidia. Moreover, the defect of rodlets on the conidial cell wall surface impacts on the drug sensitivity of the fungus.
Highlights
Hydrophobins are low molecular weight proteins with remarkable physicochemical properties secreted by filamentous fungi [1,2]
Seven hydrophobins were found in A. fumigatus, classification of RodD is controversial
In the closely-related species A. nidulans, six hydrophobins were found in the genome
Summary
Hydrophobins are low molecular weight proteins with remarkable physicochemical properties secreted by filamentous fungi [1,2]. In general, hydrophobins show low sequence conservation, these proteins are characterized by their hydrophobicity profiles and an idiosyncratic pattern of eight conserved cysteine residues that form four disulfide linkages. The surfactant and amphipathic nature of the hydrophobin layers help in the formation of essential aerial structures of filamentous fungi, such as hyphae, fruiting bodies, and spores [3]. Based on their hydrophobicity pattern, morphology of the monolayers they form and their solubility in detergents, hydrophobins are divided in two classes. Class I hydrophobins form functional amyloid fibers organized in layers with rodlet morphology, while Class II hydrophobin layers show no
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