Human serum albumin stability and toxicity of anthraquinone dye alizarin complexone: An albumin–dye model

The complexation between the primary vector of ligands in blood plasma, human serum albumin (HSA) and a toxic anthraquinone dye alizarin complexone, was unmasked by means of circular dichroism (CD), molecular modeling, steady state and time-resolved fluorescence, and UV/vis absorption measurements. The structural investigation of the complexed HSA through far-UV CD, three-dimensional and synchronous fluorescence shown the polypeptide chain of HSA partially destabilizing with a reduction of α-helix upon conjugation. From molecular modeling and competitive ligand binding results, Sudlow's site I, which was the same as that of warfarin–azapropazone site, was appointed to retain high-affinity for alizarin complexone. Moreover, steady state fluorescence displayed that static type and Förster energy transfer is the operational mechanism for the vanish in the tryptophan (Trp)-214 fluorescence, this corroborates time-resolved fluorescence that HSA–alizarin complexone adduct formation has an affinity of 105 M−1, and the driving forces were found to be chiefly π–π, hydrophobic, and hydrogen bonds, associated with an exothermic free energy change. These data should be utilized to illustrate the mechanism by which the toxicological action of anthraquinone dyes is mitigated by transporter HSA.

HSA–dye complexation induces destabilizing of the polypeptide chain of protein, ascends the hydrophilicity and leads to spatial structural changes. Dye situates within subdomain IIA of HSA, as well as the amino acid residues, such as Phe-211, Trp-214, Arg-218, Arg-222, Phe-223, Leu-238, His-242, Leu-260, and Ala-291, which all keep an appropriate distance involved in forming π–π, hydrophobic, and hydrogen bonds with dye.Figure optionsDownload as PowerPoint slideHighlights
► Dye binding alters HSA spatial structure, leading to destabilizing of HSA.
► Subdomain IIA of HSA is assigned to possess high-affinity for dye.
► Anthraquinone dye strong complex with HSA.
► HSA–dye complexation is more hydrophilic than hydrophobic.
► Static type is dominance for the reduction of Trp-214 fluorescence.