Characterization of the binding of chrysoidine, an illegal food additive to bovine serum albumin

- The binding stoichiometry of chrysoidine to BSA is 1:15.5.
- Sudlow site I in domain IIA is identified as the most possible binding site.
- Van der Waals and hydrogen bonding interactions play a major role in the binding.
- No detectable conformational change of BSA is observed during the binding process.
- Förster resonance energy transfer occurred between BSA and chrysoidine.

Chrysoidine is an industrial azo dye and the presence of chrysoidine in water and food has become an environmental concern due to its negative effects on human beings. Binding of dyes to serum albumins significantly influence their absorption, distribution, metabolism, and excretion properties. In this work, the interactions of chrysoidine with bovine serum albumin (BSA) were explored. Isothermal titration calorimetry results reveal the binding stoichiometry of chrysoidine to BSA is 1:15.5, and van der Waals and hydrogen bonding interactions are the major driving force in the binding of chrysoidine to BSA. Molecular docking simulations show that chrysoidine binds to BSA at a cavity close to Sudlow site I in domain IIA. However, no detectable conformational change of BSA occurs in the presence of chrysoidine as revealed by UV-vis absorption, circular dichroism and fluorescence spectroscopy studies.