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Potential Protein Toxicity of Synthetic Pigments: Binding of Poncean S to Human Serum Albumin

Hong-Wen Gao ^*, Qing Xu , Ling Chen ^*, Shi-Long Wang , Yuan Wang , Ling-Ling Wu  and Yuan Yuan ^*

^* State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering; Key Laboratory of Yangtze Water Environment of Ministry of Education; and School of Life Science, Tongji University, Shanghai 200092, P. R. China

Correspondence: Address reprint requests to Prof. H. W. Gao, Tel./Fax: 86-21-6598-8598; E-mail: hwgao{at}mail.tongji.edu.cn.

Using various methods, e.g., spectrophotometry, circular dichroism, and isothermal titration calorimetry, the interaction of poncean S (PS) with human serum albumin (HSA) was characterized at pH 1.81, 3.56, and 7.40 using the spectral correction technique, and Langmuir and Temkin isothermal models. The consistency among results concerning, e.g., binding number, binding energy, and type of binding, showed that ion pair electrostatic attraction fixed the position of PS in HSA and subsequently induced a combination of multiple noncovalent bonds such as H-bonds, hydrophobic interactions, and van der Waals forces. Ion pair attraction and H-bonds produced a stable PS-HSA complex and led to a marked change in the secondary structure of HSA in acidic media. The PS-HSA binding pattern and the process of change in HSA conformation were also investigated. The potentially toxic effect of PS on the transport function of HSA in a normal physiological environment was analyzed. This work provides a useful experimental strategy for studying the interaction of organic substances with biomacromolecules, helping us to understand the activity or mechanism of toxicity of an organic compound.