Aspergillus Hydrophobins: Physicochemical Properties, Biochemical Properties, and Functions in Solid Polymer Degradation

Abstract

Hydrophobins are small amphipathic proteins conserved in filamentous fungi. In this review, the properties and functions of Aspergillus hydrophobins are comprehensively discussed on the basis of recent findings. Multiple Aspergillus hydrophobins have been identified and categorized in conventional class I and two non-conventional classes. Some Aspergillus hydrophobins can be purified in a water phase without organic solvents. Class I hydrophobins of Aspergilli self-assemble to form amphipathic membranes. At the air–liquid interface, RolA of Aspergillus oryzae self-assembles via four stages, and its self-assembled films consist of two layers, a rodlet membrane facing air and rod-like structures facing liquid. The self-assembly depends mainly on hydrophobin conformation and solution pH. Cys4–Cys5 and Cys7–Cys8 loops, disulfide bonds, and conserved Cys residues of RodA-like hydrophobins are necessary for self-assembly at the interface and for adsorption to solid surfaces. AfRodA helps Aspergillus fumigatus to evade recognition by the host immune system. RodA-like hydrophobins recruit cutinases to promote the hydrolysis of aliphatic polyesters. This mechanism appears to be conserved in Aspergillus and other filamentous fungi, and may be beneficial for their growth. Aspergilli produce various small secreted proteins (SSPs) including hydrophobins, hydrophobic surface–binding proteins, and effector proteins. Aspergilli may use a wide variety of SSPs to decompose solid polymers.

Comparative genomics of the extremophileCryomyces antarcticusand other psychrophilic Dothideomycetes

“…The contraction of hydrophobic surface-binding proteins among the psychrophiles may be due to the involvement of hydrophobins in water-sensing mechanisms during spore germination. Hydrophobins contributes to surface hydrophobicity needed for conidial dispersal, and protection against a host defense system, (Tanaka et al ., 2022), all of which are essential processes for pathogenic or symbiotic interactions, but are not required in psychrophilic fungi. In plant pathogens like M. grisea and F. graminearum, hydrophobins are required for production of infective structures, penetration of the water-air interface of the host and attachment to hydrophobic surfaces (Talbot, Ebbole and Hamer, 1993; Quarantin et al ., 2019).…”

Hydrophobin Thfb6 from <em>Trichoderma harzianum</em> Induces Systemic Resistance in Tobacco Against Tobacco Mosaic Virus

“…There are multiple hydrophobin-coding genes in fungal genomes with low sequence similarity, while only a few of them have been studied. For example, Aspergillus contains six to eight hydrophobic protein genes that have little amino acid sequence homology, except for eight cysteines [28], and different functions [29]. Some hydrophobins of pathogenic fungi are closely related to their pathogenicity, such as VdHP1, a hydrophobin that plays an important role in the development, adaptability, and virulence of Verticillium dahlia [30].…”

Morphology of Penicillium rubens Biofilms Formed in Space

“…This is due to hydrophobins, which are proteins that help to determine a fungal spores' hydrophobicity. One hydrophobin, RodA, has been shown to coat the outside of spores, forming a hydrophobic rodlet layer in Aspergillus fumigatus, and other hydrophobins have been identified in hyphae [45][46][47]. An ortholog RodA gene with 100% query cover (E value 0.0, and 90.40% identity) was found in P. rubens (Accession No.…”