Multi-spectroscopic analysis and molecular modeling on the interaction of curcumin and its derivatives with human serum albumin: A comparative study

• Removing of methoxyl groups is benefit for binding on site II of HSA.
• Demothxycurcumin influences the α-helix structure greater at low concentrations.
• Bisdeoxycurcumin unfolds the protein more efficient at high concentrations.
• Docking results explain the quenching behavior and preference of binding site.

The comparative study about the interaction between curcumin and its derivatives (demothxycurcumin and bisdeoxycurcumin) with human serum albumin (HSA) has been carried out using multi-spectroscopic analysis and molecular modeling method. The characteristic of fluorescence quenching and the thermodynamic parameters have been studied by state emission fluorescence experiments under different temperatures with an interval of 6 K. Curcumin shows largest quenching constant and bisdeoxycurcumin shows the smallest at the temperature of 298 K. However, the quenching constant of curcumin drops quickly with the increase of temperature. Demothxycurcumin gives the largest quenching efficiency at the temperature of 310 K. An average distance of 6.7 nm for energy transfer has been determined based on förster resonance energy theory (FRET). The site competitive replacement experiments illustrate three compounds mainly binding on site I (Subdomain IIA) of the protein, and show tendency of binding on site II (Subdomain IIIA) with the removing of methoxyl groups. Circular dichroism spectra and Fourier transform infrared spectroscopy (FTIR) have been used to investigate the influence on protein secondary structure. Content of the α-helix increases at low concentrations of the compounds, while unfolding occurs at high concentrations. Docking simulation reveals possible mechanism for different quenching behavior and binding sites preferred by three compounds. The binding modes have effectively supported the conclusion of the experiments.

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