Interaction of bovine serum albumin with ellagic acid and urolithins A and B: Insights from surface plasmon resonance, fluorescence, and molecular docking techniques

Human serum albumin (HSA) shows the sequence homology and structural similarity with bovine serum albumin (BSA). Therefore, here, the interaction of natural phenolic antioxidants, ellagic acid (ELA), and its derivatives–urolithins A (ULA) and B (ULB)–with BSA was investigated. The results of surface plasmon resonance (SPR) indicated a high affinity of ELA, ULA, and ULB to BSA, with K_D value < 1 × 10⁻⁶ M. The K_D values of binding of the studied compounds to BSA increased with temperature, revealing a reduction in affinity with an increase in temperature. Fluorescence data showed that the quenching of BSA by tested compounds occurred via a static quenching. However, the affinity of ELA for BSA was higher than that of ULA and ULB, which may be because of the presence of a large number of hydroxyl groups in its structure. The assessment of the antioxidant activity of BSA and BSA–ELA/ULA/ULB complexes using the DPPH assay indicated that the DPPH scavenging activity of BSA increased after complex formation with ELA/ULA/ULB in the following order: BSA–ELA > BSA-ULA > BSA-ULB > BSA, which was due to their structural differences. The results of the docking analysis were in agreement with the experimental results.