A comparative study on binding ability of three lanthanide ions with centrin using impedance method

Abstract

Centrin, an EF-hand calcium-binding protein, is involved in the formation of the microtubule organizing center (MTOC). The interactions between Gd3+, Eu3+, La3+ and the N-terminal domain of ciliate Euplotes octocarinatus centrin (N-EoCen) were investigated by electrochemical impedance spectroscopy (EIS) using potassium ferricyanide as a redox probe. Results show that an increase in the lanthanide ion (Ln3+) concentration resulted in a lower impedance magnitude in the Nyquist plots when the N-EoCen-modified glassy carbon electrode (N-EoCen-GC) was used. The titrations of N-EoCen with Ln3+ confirm the complexation reactivity of Ln3+ with N-EoCen and suggest that the Ln2–N-EoCen complex was formed. In contrast, the binding ability of Ca2+ to N-EoCen is far less than that of Ln3+. The binding constants of the metal ions to N-EoCen are in the order of Gd3+ ≈ Eu3+ > La3+ ≫ Ca2+. Compared with the resonance light scattering (RLS) method, the EIS method can not only distinguish the binding ability of different metal ions to N-EoCen, but can also distinguish clearly the different metal ion binding sites on N-EoCen.