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

Abstract

The non-covalent interaction of reactive brilliant red (RBR) as a representative of sulfonic azo compounds with human serum albumin (HSA) was investigated by a combination of UV-VIS spectrometry, fluorophotometry, circular dichroism (CD) and isothermal titration calorimetry (ITC) technique. The thermodynamic characterization of the interaction was performed. The saturation binding numbers of RBR on peptide chains were determined and the effects of electrolytes and temperature were investigated. The ionic interaction induced a combination of multiple non-covalent bonds including hydrogen 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 of RBR to HSA was less than 40 and RBR molecules entered the hydrophobic intracavity of HSA when ratio was more than 40. Moreover, RBR binding resulted in a conformational change in the structure of HSA or even the precipitation of HSA and inhibited its function accordingly. The possible binding site and the conformational transition of HSA were hypothesized and illustrated. This work provides a new insight into non-covalent interactions between sulfonic azo compounds and proteins, which may be further used to investigate the potential toxicity mechanism of azo dyes.

Applications of isothermal titration calorimetry in pure and applied research—survey of the literature from 2010

“…Protein interactions with other proteins Protein interactions with small ligands (including co‐factors and drugs) Protein/peptide interactions with metals and ions …”

Modification of the structural stability of human serum albumin in rheumatoid arthritis

“…Nevertheless, most of the C3 modification sites such as those in the plausible domain I binding pocket (K12, K199, K281, S287, H288, and Y452) are known to be high affinity binding sites for drugs or other protein interactors [76][77][78][79][80][81][82][83][84][85][86][87][88][89]. Table 2 shows which of the C1, C2, and C3 sites have been associated with ligands, drug, or protein binding sites in previous studies [76][77][78][79][80][81][82][83][84][85][86][87][88][89]. For all other sites, reactivity has still been observed [90][91][92].…”

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“…The heart-shaped molecule is assembled from three homology domains (I–III). , Each domain contains two subdomains (A and B), and the subdomains A and B contain 6 and 4 α-helices, respectively, which are connected by flexible loops and connected by van der Waals forces, hydrophobic interactions, and ionic bonds. Hydrogen bonding and other forces maintain its three-dimensional structure. , HSA is mainly synthesized in the liver, which is a very abundant and important nutrient, , performing important physiological functions in the body: (1) Maintenance of plasma osmotic pressure: HSA needs to be maintained at normal concentrations to maintain normal plasma osmotic pressure (the content of HSA in human plasma is generally 35–50 g/L, and the content in urine is below 30 mg/L); abnormal levels of HSA in blood and urine can be used as early signs of some diseases, and it is one of the important indicators in routine blood examination. High abnormal levels can increase blood viscosity and induce cardiovascular disease, hypertension, diabetes, kidney disease, etc.…”