Impact of cofactor on stability of bacterial (CopZ) and human (Atox1) copper chaperones

Here, we present the first characterization of in vitro unfolding and thermodynamic stability of two copper chaperone proteins: Bacillus subtilis CopZ and Homo sapiens Atox1. We find that the unfolding reactions for apo- and Cu(I)-forms of CopZ and Atox1, induced by the chemical denaturant, guanidine hydrochloride (GuHCl), and by thermal perturbation are reversible two-state reactions. For both proteins, the unfolding midpoints shift to higher GuHCl concentrations and the thermodynamic stability is increased in the presence of Cu(I). Despite the same overall fold, apo-CopZ exhibits much lower thermal stability than apo-Atox1. Although the thermal stability of both proteins is increased in the presence of copper, the stabilizing effect is largest for the less stable variant. Divergent energetic properties of the apo- and holo-forms may be linked to conformational changes that facilitate copper transfer to the target.