Mechanical folding and unfolding of the redox protein Flavodoxin

Abstract

We investigate the unfolding and folding processes of redox protein Flavodoxin under the action of mechanical forces at the single molecule level using force spectroscopy methods with optical tweezers. Previous bulk studies have provided valuable information about the structure of the folded and unfolded states, and pointed out the existence intermediate states along the unfolding and folding pathways. However direct evidence about the existence of such kinetic intermediates and their lifetimes is still missing. Here we pull molecular constructs of the protein Flavodoxin flanked by double stranded DNA linkers tethered to micron-sized beads with optical tweezers to mechanically unfold the protein. The distributions of rupture forces have been characterized and intermediate states have been found along the unfolding and folding pathways. Moreover, the molecular free energy landscape of the protein has been characterized from the unfolding kinetics using the Bell-Evans model and an estimate of the free energy of formation of the protein has been extracted using the Crooks fluctuation theorem