Interaction mechanism of Cu+/Cu2+ on bovine serum albumin: Vitro simulation experiments by spectroscopic methods

Copper (Cu) is an essential trace element for organisms, while excessive concentration of Cu is toxic. In order to assess the toxicity risk of copper in different valences, FTIR, fluorescence, and UV-vis absorption techniques were conducted to study the interactions between either Cu⁺ or Cu²⁺ and bovine serum albumin (BSA) under vitro simulated physiological condition. The spectroscopic analysis demonstrated that the intrinsic fluorescence emitted by BSA could be quenched by Cu⁺/Cu²⁺ via static quenching with binding sites 0.88 and 1.12 for Cu⁺ and Cu²⁺, respectively. On the other hand, the constants of Cu⁺ and Cu²⁺ are 1.14 × 10³ L/mol and 2.08 × 10⁴ L/mol respectively. ΔH is negative whereas ΔS is positive, showing that the interaction between BSA and Cu⁺/Cu²⁺ was mainly driven by electrostatic force. In accordance with Föster's energy transfer theory, the binding distance r showed that the transition of energy from BSA to Cu⁺/Cu²⁺ is highly likely to happen. BSA conformation analyses indicated that the interactions between Cu⁺/Cu²⁺ and BSA could alter the secondary structure of proteins. Current study provides more information of the interaction between Cu⁺/Cu²⁺ and BSA, and reveals the potential toxicological effect of different speciation of copper at molecular level.

Revealing the complexity of distinct manganese species-protein interactions through multi-spectroscopy

The effect of manganese (Mn) on protein conformation is closely related to its chemical species. To further realize the behavior of different species of Mn in vivo, this study is designed to analyze the separate and simultaneous interactions of Mn(ii) and Mn(iii) with bovine serum albumin (BSA) using multi-spectroscopy. The results demonstrated that the interaction of Mn(ii) or Mn(iii) with BSA is a process of static quenching and Mn(iii) formed a more stable complex. The binding constants and thermodynamic constants indicated that a 1:1 complex was formed between Mn(ii)/Mn(iii) and BSA through a moderate binding force, and hydrophobic interaction played an important role in the binding. UV-Vis spectroscopy, synchronous fluorescence spectroscopy and three-dimensional fluorescence spectroscopy results revealed that the conformation changes in BSA induced by Mn(ii)/Mn(iii) binding. The results of the ternary systems suggested that both Mn species interfered the interaction of the other with BSA. The conformation of BSA may change more to adapt to the simultaneous binding to Mn (ii) and Mn (iii) when two Mn species coexist.