Binding of Reactive Brilliant Red to Human Serum Albumin: Insights intothe Molecular Toxicity of Sulfonic Azo Dyes

摘要

The non-covalent interaction of reactive brilliant red (RBR) as a representative of sulfonic azo compounds withhuman serum albumin (HSA) was investigated by a combination of UV-VIS spectrometry, fluorophotometry, circular di-chroism (CD) and isothermal titration calorimetry (ITC) technique. The thermodynamic characterization of the interactionwas performed. The saturation binding numbers of RBR on peptide chains were determined and the effects of electrolytesand temperature were investigated. The ionic interaction induced a combination of multiple non-covalent bonds includinghydrogen bonds, hydrophobic interactions and van der Waals force. A three-step binding model of RBR was revealed.The binding of RBR molecules might occur on the external surface of HSA via electric interaction when the mole ratio ofRBR to HSA was less than 40 and RBR molecules entered the hydrophobic intracavity of HSA when the ratio was morethan 40. Moreover, RBR binding resulted in a conformational change in the structure of HSA or even the precipitation ofHSA and inhibited its function accordingly. The possible binding site and the conformational transition of HSA were hy-pothesized and illustrated. This work provides a new insight into non-covalent interaction between a sulfonic azo com-pound and protein, which may be further used to investigate the potential toxicity of azo dyes.