Probing the interaction between 7-O-β-D-glucopyranosyl-6-(3-methylbut-2-enyl)-5,4′-dihydroxyflavonol with bovine serum albumin (BSA)

Serum albumin is the most abundant protein in the circulatory system. It plays an important role in the transport and deposition of many molecules in the body. The 7-O-beta-glucopyranosyl-6-(3 -methylbut-2-eny1)-5,4'-dihydroxyflavonol (PF) is a glycosylated flavonoid isolated from Ouratea hexasperma (Ochnaceae) branches. It shows important biological activities, such as cytotoxic, antimicrobial and antitumor. The aim of this study was to examine the interaction of bovine serum albumin (BSA) with PF in a PBS buffer solution (pH = 7.4) at 296 K, 303 K and 310 K, by spectroscopic techniques (UV-vis, circular dichroism, FTIR-ATR, steady-state, time-resolved, synchronous and 3D fluorescence) and molecular docking. The experimental results showed that the intrinsic fluorescence quenching of BSA induced by PF resulted in an association BSA:PF in the ground state (k(q) 10(12) M-1 s(-1)). The association is moderate with K-a approximate to 10(4) M-1 and K-b approximate to 10(5) M-1. The CD, 3D and synchronous fluorescence, as well as FTIR-ATR results indicate that the association BSA:PF does not result in a significant perturbation on the secondary structure of BSA. Forster resonance energy transfer (FRET) is not operating in the present case. The negative values for Delta G degrees are in accord with the spontaneity of the interaction. Delta H degrees < 0 and Delta S degrees > 0 indicate an enthalpically and also entropically driven association and the main interaction forces between BSA:PF are hydrogen bonding and/or electrostatic forces. The number of binding sites (n approximate to 1) indicate only one main binding site for the interaction BSA:PF. The competitive binding studies indicate Trp-212-containing binding site as the main pocket for the interaction BSA:PF and molecular docking results also suggest the same cavity. Inside this site, the amino acid residues Glu-152, Arg-194, Arg-198, Arg-217, Ser-343, Asp-450 and Ser-453 interact by hydrogen bond with PF, whereas Ala-341 and Val-342 residues interact by hydrophobic interactions. (C) 2016 Elsevier B.V. All rights reserved.