Physical Properties of Yeast Prion Proteins Studied with Optical Tweezers

Abstract

Formation of amyloid fibers plays a vital role in both natural biological processes and neurodegenerative disease. Recently, amyloid formation has been shown to be a general property of proteins and peptides. Their impressive mechanical properties, which are comparable to spider silk, combined with their ease of assembly in synthetic preparations make amyloid fibers particularly suited for nanomaterials applications, including as templates for conducting nanowire formation, as scaffolds for cell growth, and as functionalized biosensors. Prion proteins are a special class of amyloid fiber forming proteins which are self-templating and thereby transmissible as disease vectors. This work combines optical tweezers force spectroscopy with fluorescence imaging to study the physical properties of amyloid fibers formed from polymorphic variants of a 253 amino acid N-terminal fragment (NM) of the yeast prion protein Sup35. Experiments revealed that fibers associated with a “weak” NM prion strain have an approximately 2-fold larger bending stiffness than those associated with a “strong” NM prion strain. We further subjected NM fibers to multiple cycles of forces up to 250 pN resulting in unfolding of individual prion subdomains and rupture of intermolecular interactions. Our results have implications for the physical basis of prion strain diversity and give important insights into the underlying structure of Sup35 prions.