Objective: Protein nanofibrils, or amyloid fibrils, could serve as building-blocks for functional nanomaterials in a range of applications, including in food. Rational design of functional amyloid materials requires a better understanding of nanofibril self-assembly. This study examined cross-seeding reactions between two unique nanofibril polymorphs, one long and flexible and the other short and rigid, of lysozyme from two species (human and chicken).
Methods: Different nanofibril polymorphs were formed under conditions of pH 2 and pH 6.3, and these were subsequently treated by sonication and proteolysis to replicate processing and digestion conditions to create ‘seeds’. The kinetics of nanofibril formation were measured using ThT fluorescence, and fibril morphology was analyzed using TEM.
Results: Both polymorphs could cross-seed aggregation across species, but this reaction was markedly reduced under physiological conditions. For both species, the pH 6.3 fibril polymorph was dominant, seeding fibril growth with a faster elongation rate at pH 2 than the pH 2 polymorph. Based on fibrillation kinetics and fibril morphology, we found that the pH 2 polymorph was not able to faithfully replicate itself at pH 6.3.
Conclusions: These results show that two distinct amyloid polymorphs are capable of heterologous seeding across two species (human and hen) of lysozyme, but that the pH 6.3 polymorph is favoured, regardless of the species, likely due to a lower activation barrier to accessing this particular misfolded form. These findings contribute to our better understanding of amyloid strain propagation across species barriers, which has implications for understanding pathological amyloid and engineering functional amyloid.