Folding and unfolding of proteins

Abstract

Single-molecule atomic force spectroscopy probes elastic properties of proteins such as titin and ubiquitin. We analyze bioprotein folding dynamics under both force and length-clamp conditions by modeling polyprotein modules as particles in a bistable potential, connected by harmonic springs. The study of multistable equilibria in these models explains recorded sawtooth force-extension curves. We show that bifurcations and transitions through quasi-stationary domain configurations modified by thermal noise are involved in observed stepwise and abrupt refolding and unfolding phenomena under force-clamp conditions. These predictions agree with experimental observations.