Influence of metal ions on folding pathway and conformational stability of bovine serum albumin

In order to understand the effects of metal ions on the structural stability of proteins, urea-induced unfolding transition of bovine serum albumin (BSA) in the presence of different kinds of metal ions (Zn2+, Ca2+, Cd2+ and Co2+) are characterized by far-UV circular dichroism (CD) and fluorescence spectra. Under neutral condition, there is a significant deviation of the unfolding transition curves of free protein by fluorescence and CD spectra. However, the unfolding curves of fluorescence and CD spectra turn to be coincident in the presence of Ca2+ or Cd2+ ions, indicating that the tertiary and secondary structures of BSA unfold simultaneously, i.e. a cooperative two-state behavior, while the deviation of them is enhanced in the presence of Zn2+ or Co2+ ions, suggesting that the unfolding remains a three-state behavior. Our results provide evidence that the metal ions alter the urea-induced unfolding pathway of BSA. Furthermore, the change of free energy (ΔG), the midpoint of chemical denaturation (Cm) and the solvent-exposed surface (m) during the urea-induced unfolding process have also been obtained to characterize the effects of metal ions on the conformational stability of BSA.