Elucidating the interaction between equisetin and human serum albumin: A comprehensive study using spectroscopy, microcalorimetry and molecular docking approaches

Equisetin, a bioactive compound of marine origin, offers compelling inhibitory properties against HIV-1 transcriptase. To gain comprehensive insights into the interaction of Equisetin with human serum albumin (HSA), we utilized a multipronged approach involving spectroscopy, isothermal titration calorimetry (ITC) and molecular docking. Our fluorescence analyses confirmed that the interaction between Equisetin and HSA results in a significant quenching of HSA's fluorescence, primarily achieved through a dynamic mechanism aided by hydrogen bonding and van der Waals forces. Isothermal titration calorimetry (ITC) measurements revealed an impressive binding affinity of Equisetin for HSA, quantified to be 4.3 x 107 mol L- 1. Molecular docking studies illustrated that Equisetin binds at site III of HSA, with specific amino acid residues, GLN-104 and LYS-106, playing a pivotal role. Further, our study discovered that the interaction induces slight unfolding of HSA's polypeptide chain and significant alterations in its secondary structure, thereby triggering the exposure of previously concealed hydrophobic regions. This comprehensive study enhances our understanding of Equisetin's interaction with serum proteins, potentially influencing its pharmacokinetics and pharmacodynamics, and opening avenues for future research and therapeutic applications.