Polyphenols such as epigallocatechin gallate (EGCg) are components in plant-based foods and beverages, such as green tea, and may have roles in preventing diseases like cardiovascular disease. Human serum albumin (HSA) is a multi-domain protein, which binds various ligands and aids in many physiological functions involving transport, distribution and metabolism in the circulatory system. Previous research suggests that HSA undergoes conformational change upon binding of certain ligands such as fatty acids. Since EGCg binds to HSA tightly, we hypothesize that EGCg induces conformational change in HSA. In the present study, FRET was used to determine the inter- and intra-domain distances of HSA. HSA has a single Trp-214, and was labeled with one of two fluorescence probes, prodan (6-propionyl-2-(dimethylamino)-naphthalene) and CPM (7-diethylamino-3-(4-maleimidophenyl)-4-methylcoumarin) at the warfarin binding site and Cys-34, respectively. Fluorescence and absorbance were measured to calculate the distance between pairs of fluorophores. EGCg (5 μM-50 μM) was titrated into 1 μM HSA, and the distances were measured to test the hypothesis that EGCg affects HSA conformation. The results showed that the distance between Trp-214 and prodan was ~ 25 Å, and the distance between Trp-214 and CPM-Cys-34 was ~30 Å. When EGCg was added to HSA, the Trp-prodan distance did not change. However, the distance between Trp-214 and CPM-Cys-34 increased up to 34 Å in the presence of 25 μM and 50 μM EGCg. Therefore, the biggest conformational change induced by EGCg was about 4 Å. Since FRET can only detect distances smaller than 60 Å, results from dynamic light scattering and circular dichroism approaches will be discussed.

Human serum albumin is conformationally changed in the presence of epigallocatechin gallate using FRET (Förster resonance energy transfer)

255th National Meeting (2018)

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