Self-assembly of MPG1, a hydrophobin protein from the rice blast fungus that forms functional amyloid coatings, occurs by a surface-driven mechanism

Abstract

Rice blast is a devastating disease of rice caused by the fungus Magnaporthe oryzae and can result in loss of a third of the annual global rice harvest. Two hydrophobin proteins, MPG1 and MHP1, are highly expressed during rice blast infections. These hydrophobins have been suggested to facilitate fungal spore adhesion and to direct the action of the enzyme cutinase 2, resulting in penetration of the plant host. Therefore a mechanistic understanding of the self-assembly properties of these hydrophobins and their interaction with cutinase 2 is crucial for the development of novel antifungals. Here we report details of a study of the structure, assembly and interactions of these proteins. We demonstrate that, in vitro, MPG1 assembles spontaneously into amyloid structures while MHP1 forms a non-fibrillar film. The assembly of MPG1 only occurs at a hydrophobic:hydrophilic interface and can be modulated by MHP1 and other factors. We further show that MPG1 assemblies can much more effectively retain cutinase 2 activity on a surface after co-incubation and extensive washing compared with other protein coatings. The assembly and interactions of MPG1 and MHP1 at hydrophobic surfaces thereby provide the basis for a possible mechanism by which the fungus can develop appropriately at the infection interface.

Characterization of a Basidiomycota hydrophobin reveals the structural basis for a high-similarity Class I subdivision

“…SC16 maintained the key features of the hydrophobin fold: a central four-strand β-sheet and four disulphide bonds (Fig. 2)81920212223. Notably, in solution its sheet adopted a compact β-barrel structure more similar to the core structures of the Class II hydrophobins HFBI and HFBII (backbone atom root mean squared deviation of 3.0 Å and 2.2 Å, respectively; Fig.…”

“…Closer inspection revealed this surface to comprise several backbone amide groups and side chain hydroxyl groups but lack hydrophobic side chain groups. This observation is unusual as other Class I hydrophobins typically display large exposed hydrophobic regions, which have been hypothesized to be responsible for mediating self-assembly at hydrophobic interfaces81920.…”

“…Analysis of the surface charge distribution of SC16 revealed several acidic, basic, and uncharged patches (Figure S4) but the latter, in particular, was not as prominent for SC16 as for EAS, DewA and MPG181920. Closer inspection revealed this surface to comprise several backbone amide groups and side chain hydroxyl groups but lack hydrophobic side chain groups.…”

“…While hydrophobins from both phyla have been characterized, high-resolution structures exist only for those of ascomycota origin: the Class I EAS, DewA, MPG1, and Class II NC2, HFBI, and HFBII81920212223. To address whether basidiomycota hydrophobins share structural and functional features with these proteins, we preliminarily characterized SC16 ( hyd1 ) from Schizophyllum commune and determined its structure.…”

MoVrp1, a putative verprolin protein, is required for asexual development and infection in the rice blast fungus Magnaporthe oryzae

“…In M. oryzae, MPG1 and MHP1 facilitate fungal spore adhesion, and to direct the action of the enzyme cutinase 2, resulting in penetration of the plant host52. Knockout of MPG1 and MHP1 results in the impaired appressorium development and reduced infectivity5354.…”