Binding of copper to lysozyme: Spectroscopic, isothermal titration calorimetry and molecular docking studies

• This work studied the interacting mechanism of copper with lysozyme.
• Copper could spontaneously interact with lysozyme through hydrophobic forces.
• Binding of copper to lysozyme was a static quenching process.
• Copper induced the conformational changes of lysozyme.
• Copper could affect the function of lysozyme by inhibiting its catalytic activity.

Although copper is essential to all living organisms, its potential toxicity to human health have aroused wide concerns. Previous studies have reported copper could alter physical properties of lysozyme. The direct binding of copper with lysozyme might induce the conformational and functional changes of lysozyme and then influence the body's resistance to bacterial attack. To better understand the potential toxicity and toxic mechanisms of copper, the interaction of copper with lysozyme was investigated by biophysical methods including multi-spectroscopic measurements, isothermal titration calorimetry (ITC), molecular docking study and enzyme activity assay. Multi-spectroscopic measurements proved that copper quenched the intrinsic fluorescence of lysozyme in a static process accompanied by complex formation and conformational changes. The ITC results indicated that the binding interaction was a spontaneous process with approximately three thermodynamical binding sites at 298 K and the hydrophobic force is the predominant driven force. The enzyme activity was obviously inhibited by the addition of copper with catalytic residues Glu 35 and Asp 52 locating at the binding sites. This study helps to elucidate the molecular mechanism of the interaction between copper and lysozyme and provides reference for toxicological studies of copper.

Copper could spontaneously bind lysozyme through hydrophobic forces with a positive ΔH, a favorable ΔS, and a negative ΔG. Binding of copper to lysozyme caused static quenching of the fluorescence, the change of the microenvironment of tryptophan residues and conformational changes of lysozyme. Besides, the lysozyme activity was also inhibited by the addition of copper with catalytic residues Glu 35 and Asp 52 locating at the binding sites. Thus, the direct interaction between copper and lysozyme might induce the conformational and functional alterations of lysozyme.Figure optionsDownload as PowerPoint slide