In the past 20 years, there has been a growing understanding of the multiple diverse roles played by functional amyloids in different organisms, including in mammals, bacteria, viruses and fungi. In filamentous fungi, amyloid is utilized to increase infectivity1. Currently, diseases caused by Aspergillus fumigatus and Magnaporthe oryzae pose a serious risk to humans and plants. A. fumigatus is responsible for invasive aspergillosis, a disease that infects the human lung and can subsequently spread to the brain and/or kidneys. A. fumigatus utilises small amyloid-forming proteins called hydrophobins (RodA and RodB) to evade immune detection and therefore cause infection. Magnaporthe oryzae causes rice blast disease, a disease responsible for destroying a third of the annual global rice crop. M. oryzae also uses an amyloid-forming hydrophobin (MPG1) to increase its pathogenicity and to transition through its life cycle. Given the role of functional amyloid in increasing fungal infectivity, disruption of fungal amyloid formation may be a new approach to preventing these diseases.
We have tested a series of new small-molecule compounds against functional amyloid formation by hydrophobin proteins, and against pathogenic amyloid assembly by the Abeta peptide that forms amyloid in Alzheimer’s disease. We find that some of these small molecules are able to prevent assembly of both functional and pathogenic amyloids. However, the mechanism of action against these two types of amyloid appears to be different.
Hydrophobin proteins require a hydrophobic:hydrophilic interface to initiate nucleation and thus amyloid formation. These small molecules appear to restrict the hydrophobins to a monomeric state by reducing the surface tension of the medium and thus preventing amyloid formation. This interaction has been investigated by ion mobility–mass spectrometry and thioflavin T fluorescence assays. In contrast, when treated with these small molecules the Abeta peptide does not remain monomeric but instead undergoes an off-pathway amorphous aggregation. The effect of the small molecules has been monitored using thioflavin T fluorescence assays and verified using transmission electron microscopy. In addition, these small molecules have been shown to prevent Abeta-associated neuronal cell death in vivo, emphasizing their potential as leads for the development of therapeutic strategies for Alzheimer’s disease.