Surface effects on the degree of twist in amyloid fibril structures.

Amyloid fibrils, implicated in health and diseases, commonly exhibit a periodic twist trait relevant to the structures and dynamics of the fibrils. However, the origins and modulations of fibril twist in complex in vivo environments are not yet fully understood. Here we highlight an important factor that causes twist variations in amyloid fibril structures-the presence of surrounding surfaces. Using cholesterol-containing lipid bilayers with varying cholesterol contents, we have demonstrated via atomic force microscopy that amyloid-β peptide fibrils initiated on membranes increase their average pitch size of twisting periodicity as the cholesterol content increases. These surface-induced twist variations arise from the enhanced hydrophobic interactions between the fibril and the surface distorting the torsional elastic energy of the fibril twisting as supported by a theory of an elastic model. These findings not only provide an important insight into fibril polymorphism phenomena resulting from the surface effects but also suggest a novel solution to modulate filament twisting on the nanoscale for biomaterials applications involving nanoscale features.