Biophysical and in silico investigations of the molecular association between a potent RNA polymerase inhibitor, thiolutin and human serum albumin

Abstract Biomolecular association of thiolutin (TLT), a potent RNA polymerase inhibitor with albumin from human serum (HSA), the main transporter in blood plasma was examined using various biophysical and in silico techniques. An inverse correlation between the Stern-Volmer constant, KSV and temperature predicted TLT-induced quenching as the static quenching, hence suggested TLT–HSA complex formation. This was also supported by UV–vis absorption spectral results. A weak binding affinity was registered towards the complex formation, as evident from the binding constant, Ka value. Thermodynamic data obtained at different temperatures as well as molecular docking analysis revealed participation of hydrophobic and van der Waals forces as well as hydrogen bonds in TLT–HSA complexation. Binding of TLT to HSA was found to alter the microenvironment around HSA fluorophores (Tyr and Trp), as manifested by three-dimensional fluorescence spectra. Presence of TLT in association with HSA offered protection to the protein against temperature-induced destabilization. Competitive site-marker displacement experiments using warfarin, phenylbutazone and hemin identified the preferred TLT binding site as Sudlow's site I in HSA, which was also validated by molecular docking analysis. Molecular dynamics assessments disclosed that the complex reached equilibrium during simulations, indicating the stability of the TLT–HSA complex.