High pressure promotes circularly shaped insulin amyloid.

Amyloids, initially associated with certain degenerative diseases, and recently with the prions and prion-based inheritance in yeasts, are linearly-ordered beta-sheet-rich protein aggregates, presently thought to represent a rather common generic trait of proteins as polymers. Regardless of genetic origins and properties of precursor protein molecules, amyloids share many physicochemical properties, including the linear fibrillar morphology. Here, we show that under high hydrostatic pressure insulin forms amyloids of a unique circular morphology. Despite a degree of size-distribution, the smallest forms of the approximate radius of 340-420 nm are most abundant among the ring-shaped structures. The circular amyloid is accompanied by bent 20-100 nm long fibrils. The pressure-enhancement of a ring-like supramolecular fold suggests an anisotropic distribution of void volumes in regular amyloid fibres. While the ability of high pressure to evoke such drastic perturbations on an amyloidogenic pathway may help tune conformation of amyloid templates (e.g. inducing the PrP(Sc)-type infectivity in amyloids grown in vitro from recombinant PrP), the very finding raises new questions concerning possible consequences for high-pressure food processing.