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.