Repulsive interaction induces fibril formation and their growth.

In a type-II diabetes disease, amylin protein takes an incorrect structure that leads to the formation of the amyloid fibril. The conversion mechanism of amyloid fibril is not well understood. We have observed a repulsive interaction, in terms of second virial co-efficient (A2), between protein molecules in their native state in the PBS buffer through laser light scattering technique. The A2 switches from repulsive (positive A2) to attractive (negative A2) interactions with elapsed time favoring the formation and growth of the fibril. We report aggregation and fibril growth kinetics of amylin protein in different environmental conditions. The measurement of shape factor (ρ) through light scattering experiment shows a transition from coil-like structure to rod-like growth. In addition to rod-like growth, sheet-like growth of fibril is also observed through analytical and high-resolution TEM imaging techniques. The nucleation leading to elongation of fibrils as well as stacking of individual fibril perpendicular to the fibril axis is held by hydrogen bonding observed through high-resolution TEM.