A Correlative Multi-Spectroscopy and Docking Study for the Modeling of Drug (Luteolin and Quercetin) Binding to Bovine Serum Albumin– A Tool for the Determination of Binding Characteristics to Receptor Proteins

Abstract

The in vitro in silico experimental flow (multi-spectroscopy and docking) demonstrated the binding of Luteolin and Quercetin separately with Bovine Serum Albumin. For the first time, we are reporting the relative UV-visible spectroscopy-based hypsochromic shifts for both luteolin (3nm) and quercetin (4.1 nm) respectively. The drug-induced conformational change may lead to the possible shift in the tryptophan residue to a more hydrophobic environment. Our demonstration of an increased static quenching of the endogenous fluorophore in BSA validated the UV-visible spectroscopy data. However, detailed experiments will further delineate the possible relative contribution of dynamic quenching processes. The strong binding (binding constant values -10 5 L/mol) and the number of binding sites (1 for luteolin and quercetin) is consistent with published findings. Under our defined conditions, the hitherto unreported non-cooperative binding was demonstrated, based on the Hill's coefficient. Thermodynamic data qualitatively validated hydrophobicity (a positive entropy change ΔS 0 ); hydrogen bonding (a negative ΔH 0 ) and electrostatic interactions (a negative ΔH 0 and a positive ΔS 0 ). For the first time, the Infra-Red Spectroscopy (FT-IR) data showed ground state complex formation of the molecules with the model protein and may serve to corroborate our fluorescence (static quenching) data. Hydrogen bonds and hydrophobic interactions for both molecules (Ligplot Analysis) provide corroborative evidence for the molecular spectroscopy and thermodynamic data. This hitherto unreported, unique, combinatorial in vitro (multispectroscopy and thermodynamic measurements) in silico (docking and Ligplot-based analysis) experimental flow (specifically for luteolin and quercetin) provides a basis for extending such binding studies for novel receptors and/or ligands.