Molecular mechanism investigation of the neutralization of cadmium toxicity by transferrin

Abstract

Cadmium adversely affects the biological function of the liver. Transferrin might be involved in the detoxification system of cadmium. However, owing to the lack of investigation of the molecular mechanism of cadmium conjugating to transferrin, the role of transferrin in cadmium detoxification in the liver and how transferrin undergoes conformational and functional changes upon cadmium binding are not clear. In this article, we demonstrated the potential role of transferrin in the protection of the mouse primary hepatocytes against cadmium toxicity. After the incubation of hepatocytes with 10 and 100 μM CdCl₂, pretreatment with transferrin significantly attenuated the reduction of cell viability in comparison with the samples treated with CdCl₂ alone. Furthermore, a detailed molecular mechanism investigation of the interaction of CdCl₂ with transferrin was reported using biophysical methods. Multi-spectroscopic measurements showed that CdCl₂ formed complexes with transferrin and caused structural and conformational changes of transferrin. Isothermal titration calorimetry measurements revealed that transferrin has two classes of binding sites with different binding constants for CdCl₂ binding. Hydrophobic forces and electrostatic forces are the major driving forces of the interaction. Preferred specific binding sites on transferrin were identified by dialysis experiments, molecular docking studies and molecular dynamics simulations. Upon low CdCl₂ concentration exposure, no content of iron was released from transferrin because CdCl₂ preferentially binds to the surface of transferrin molecules. Upon higher CdCl₂ concentration exposure, the release of iron content from transferrin was observed due to the interaction of CdCl₂ with the key residues around iron binding sites.