Biomolecular association of an anticancer drug, leflunomide (LEF) with human serum albumin (HSA), the leading ligands carrier in human circulation was characterized using biophysical (i.e., fluorescence, absorption and voltammetric) methods and computational (i.e., molecular docking and molecular dynamics simulation) techniques. Evaluations of fluorescence, absorption and voltammetric findings endorsed the complex formation between LEF and HSA. An inverse relationship of Stern-Volmer constant-temperature and hyperchromic shift of the protein's absorption signal with addition of LEF confirmed the LEF quenched the HSA fluorescence through static process. Moderate nature of binding strength (binding constant = 2.76-4.77 × 104 M-1) was detected towards the LEF-HSA complexation, while the association process was naturally driven via hydrophobic interactions, van der Waals interactions and hydrogen bonds, as evident from changes in entropy (ΔS= + 19.91 J mol-1 K-1) and enthalpy (ΔH = - 20.09 kJ mol-1), and molecular docking assessments. Spectral analyses of synchronous and three-dimensional fluorescence validated microenvironmental fluctuations near Trp and Tyr residues upon LEF binding to the protein. LEF association with HSA significantly defended temperature-induced destabilization of the protein. Although LEF was found to attach to HSA at Sudlow's sites I and II, but exhibited greater preference toward its site I, as detected by the investigations of competitive site-marker displacement. Molecular dynamics simulation assessment revealed that the complex attained equilibrium throughout simulations, showing the LEF-HSA complex constancy.Communicated by Ramaswamy H. Sarma.
Interactive association of an antifungal drug, climbazole (CBZ) with the carrier protein in bovine circulation, bovine serum albumin (BSA) was explored by fluorescence and absorption spectroscopy along with in silico techniques. The fluorescence and absorption spectral alterations of the protein upon addition of CBZ affirmed the complex foration between CBZ and BSA. The inverse temperature dependence behaviour of the KSV values as well as the hyperchromic result of the protein's absorption signals characterized CBZ-triggered quenching of BSA fluorescence as the static quenching. A weak binding affinity (Ka = 3.12-1.90-× 103 M-1) was reported towards the CBZ-BSA association process. Interpretation of thermodynamic data (entropy change = +14.68 J mol-1 K-1 and enthalpy change = -15.07 kJ mol-1) and in silico analyses anticipated that hydrophobic forces, van der Waals forces and hydrogen bonds were the key intermolecular forces in the complex stabilization. Inclusion of CBZ to BSA produced microenvironmental perturbations around Tyr and Trp residues, and also significantly defended temperature-induced destabilization of BSA. The binding locus of CBZ was detected in the proximity of Sudlow's sites I (subdomain IIA) and II (subdomain IIIA) of BSA, exhibiting greater preference towards site II, as revealed by competitive site-marker displacement investigations and in silico analysis. The stability of the CBZ-BSA complex was further validated by the molecular dynamics simulation assessments.