Assessment of the stability and unfolding pathways of azurin from Pseudomonas aeruginosa through the combination of denaturating osmolytes

The denaturating osmolytes urea and guanidine hydrochloride (GuHCl) interact differently with azurin from Pseudomonas aeruginosa. At room temperature, even high concentrations of urea were unable to unfold the metalloprotein: instead a “partially unfolded” intermediate state is formed. In contrast, the protein unfolded state was formed at GuHCl, concentrations above ≈3 M and the unfolded state subsequently undergoes an irreversible reaction, which was studied employing absorbance and fluorescence spectroscopic techniques. The partially unfolded protein formed in the presence of urea completely unfolds upon adding GuHCl and we report a kinetic and thermodynamic study to characterize the process, taking into consideration that the unfolded state undergoes an irreversible reaction.