Multispectroscopic and Molecular Modeling Approach To Investigate the Interaction of Flavokawain B with Human Serum Albumin

Abstract

Interaction of flavokawain B (FB), a multitherapeutic flavonoid from Alpinia mutica with the major transport protein, human serum albumin (HSA), was investigated using different spectroscopic probes, i.e., intrinsic, synchronous, and three-dimensional (3-D) fluorescence, circular dichroism (CD), and molecular modeling studies. Values of binding parameters for FB-HSA interaction in terms of binding constant and stoichiometry of binding were determined from the fluorescence quench titration and were found to be 6.88 × 10(4) M(-1) and 1.0 mol of FB bound per mole of protein, respectively, at 25 °C. Thermodynamic analysis of the binding data obtained at different temperatures showed that the binding process was primarily mediated by hydrophobic interactions and hydrogen bonding, as the values of the enthalpy change (ΔH) and the entropy change (ΔS) were found to be -6.87 kJ mol(-1) and 69.50 J mol(-1) K(-1), respectively. FB binding to HSA led to both secondary and tertiary structural alterations in the protein as revealed by intrinsic, synchronous, and 3-D fluorescence results. Increased thermal stability of HSA in the presence of FB was also evident from the far-UV CD spectral results. The distance between the bound ligand and Trp-214 of HSA was determined as 3.03 nm based on the Förster resonance energy transfer mechanism. Displacement experiments using bilirubin and warfarin coupled with molecular modeling studies assigned the binding site of FB on HSA at domain IIA, i.e., Sudlow's site I.

Spectroscopic analysis on structure–affinity relationship in the interactions of different oleanane‐type triterpenoids with bovine serum albumin

“…9. The strong peak 1 (λ ex = 280 nm, λ em = 358 nm), mainly revealed the spectral characteristics of tryptophan and tyrosine residues and reflected changes in the tertiary structure of BSA, and peak 2 (λ ex = 220 nm, λ em = 358 nm), mainly exhibited the fluorescence characteristic of polypeptide backbone structures and reflected changes in the secondary structure of BSA (49)(50)(51). Peaks 3 and 4 meant the Rayleigh scattering peak (λ ex = λ em ) and the second-order scattering peak (2λ ex = λ em ), respectively.…”

Characteristics and thermodynamics of the interaction of 6-shogaol with human serum albumin as studied by isothermal titration calorimetry

“…The participation of these intermolecular forces in the binding of 6-shogaol to HSA is well-supported by the structural features of 6-shogaol, which possesses both apolar and polar characteristics (Figure 1). As suggested in earlier reports (Caruso et al, 2014;Feroz et al, 2012Feroz et al, , 2013Molina-Bolivar et al, 2014;Neamtu, Tosa, Bogdan, 2013), it is not possible to account for the observed thermodynamic parameters according to a single intermolecular-force model. Therefore, the energetics data obtained in this study seem to reflect the collective contributions of hydrophobic interactions, van der Waals forces and hydrogen bonds in 6-shogaol-HSA complexation.…”

Influence of the Ring Size on the Binding Ability of FTO Investigated by Fluorescence Spectroscopy

“…While no obvious change in the emission maxima (310 nm) was observed upon addition of W 3 (or W 4 ) when Δλ was 15 nm, synchronous fluorescence spectra obtained with Δλ=60 nm showed a blue shift from 348 to 340 nm upon W 3 (or W 4 ) addition. The observed blue shift signified a transition of the Trp residues from a polar to a less polar environment [6]. Results suggested that binding of W 3 (or W 4 ) to FTO had little effect on the microenvironment around Tyr residues but was sufficient to perturb the environment in the vicinity of the lone Trp residue from polar to slightly nonpolar.…”

“…Thus, the study on the interactions of ligands with proteins is important in understanding the action of these molecules in the body [6]. The nature and magnitude of drug-protein interaction significantly influences the biological activity of the drug.…”