Characterization of sulfasalazine-bovine serum albumin and human serum albumin interaction by spectroscopic and theoretical approach

The interaction of sulfasalazine (SZ) with the carrier proteins bovine serum albumin (BSA) and human serum albumin (HSA) was explored by fluorescence, absorption and circular dichroism (CD) spectroscopy along with in silico techniques. The spectral alteration observed in fluorescence, absorption and CD spectra upon the addition of SZ confirmed the complex formation of SZ with BSA and HSA. The inverse temperature dependence behaviour of the Ksv values as well as the increase in the protein's absorption signals after the addition of SZ indicate that SZ triggered quenching of BSA/HSA fluorescence as the static quenching. The binding affinity (kb) of the order of 106 M−1 was reported towards the BSA-SZ and HSA-SZ association process. Interpretation of thermodynamic data (enthalpy change = -93.85 kJ mol−1 and entropy change = -200.81 J mol−1 K−1 for BSA-SZ system; enthalpy change = -74.12 kJ mol−1 and entropy change = -123.90 J mol−1 K−1 for HSA-SZ system) anticipated that hydrogen bond and van der Waals forces were the main intermolecular forces in the complex stabilization. Inclusion of SZ to BSA/HSA produced microenvironmental perturbations around Tyr and Trp residues. The UV, synchronous and 3D analysis confirmed the structural alteration of proteins after SZ binding, which was supported by CD results. The binding location of SZ in BSA/HSA was detected in Sudlow's site I (subdomain IIA) and the same was revealed by competitive site-marker displacement investigations. Density functional theory study was done to comprehend the feasibility of the analysis and to optimize the structure and energy gap that validated the experimental results. This study is expected to provide deep information about the pharmacology of SZ with its pharmacokinetic properties.