The Early Steps in the Unfolding of Azurin^†

High-temperature molecular dynamics simulations were used to gain insight into the early steps in the unfolding pathway of azurin, a blue copper protein with a β-barrel structure formed by two sheets arranged in a Greek key folding topology. The results reveal that unfolding of the β-barrel in azurin is associated with dislocation of its unique α-helix with respect to the protein scaffold. Exposure of the hydrophobic core to solvent precedes complete disruption of secondary and tertiary structure, and modifications in the region around the active site are directly connected with this event. Denaturation of the protein initiates from the sheet coordinating the copper ion, and the other sheet maintains its topology. Results derived from the simulation were compared with experimental data obtained with different techniques, showing excellent agreement and providing a framework to understand the process of disruption and formation of the β-barrel in azurin.