Wild-type hen egg white lysozyme aggregation in vitro can form self-seeding amyloid conformational variants

Misfolded β-sheet-rich protein aggregates termed amyloid, deposit in vivo leading to debilitating diseases such as Alzheimer's, prion and renal amyloidosis diseases etc. Strikingly, amyloid can induce conversion of their natively folded monomers into similarly aggregated conformation via 'seeding'. The specificity of seeding is well documented in vivo for prions, where prion-variants arising from conformationally altered amyloids of the same protein, faithfully seed monomers into amyloid displaying the original variant's conformation. Thus far, amyloid variant formation is reported only for a few non-prion proteins like Alzheimer's Aβ42-peptide and β-2 microglobulin, however, their conformational cross-seeding capabilities are unexplored. While mutant human lysozyme causes renal amyloidosis, the hen egg white lysozyme (HEWL) has been extensively investigated in vitro as a model amyloid protein. Here we investigated if wild-type HEWL could form self-seeding amyloid variants to examine if variant formation is more wide-spread. We found that HEWL aggregates formed under quiescent versus agitated conditions, displayed different particle sizes, detergent stabilities & β-sheet content, and they only seeded monomeric HEWL under similar incubation conditions, but not under swapped incubation conditions thereby showing amyloid variant formation by HEWL analogous to prion variants. This may have implications to the amyloidosis caused by different mutants of human lysozyme.