Deciphering Saquinavir–Bovine Serum Albumin Interactions: Spectroscopic and Computational Insights

Bovine serum albumin (BSA) plays a crucial role as a carrier protein in plasma, binding various ligands, including drugs. Understanding the interaction between BSA and saquinavir, an antiretroviral drug, is essential for predicting its pharmacokinetics and pharmacodynamics. We employed spectroscopic approaches, including circular dichroism spectrometry and fluorescence spectroscopy, to investigate the binding of saquinavir to BSA. CD studies revealed conformational changes upon saquinavir mesylate binding, and the complex was stable up to 45°C during thermal denaturation. Saquinavir quenched the intrinsic fluorescence of BSA, indicating static quenching due to complex formation. Additionally, molecular docking simulations were performed to elucidate the favored binding site and interactions. The molecular docking results revealed that Subdomains IIA and IIB, which are proximal to Sudlow Site I, are the principal binding sites for the antiviral drug saquinavir. The ligand-bound pose of BSA also revealed that residue Trp213, which is adjacent to saquinavir, further validated the results of the fluorescence quenching assay, suggesting that residue Trp213 is quenched upon binding with saquinavir. MD simulations allowed us to explore the dynamic behavior of the BSA–saquinavir complex over time. We observed conformational fluctuations, solvent exposure, flexibility of binding pockets, free energy landscape, and binding energy. This study enhances our understanding of drug–protein interactions and contributes to drug development and optimization.