Abstract
It is important to understand the nature and mechanism of interaction of drugs with serum albumins as such interactions govern their pharmacokinetics and pharmacodynamics. Plumbagin is a natural phytocompound, mainly present in the bark of Plumbaginaceae family plants and it has numerous therapeutic potentials. In this study, the interaction of plumbagin with human serum albumin (HSA) was deciphered using an array of biophysical and computational tools. The UV-vis spectroscopy established the formation of plumbagin-HSA complex with binding constant as 2.32 x 10(4) M-1. Fluorescence spectroscopy revealed that there was static mode of quenching of HSA's fluorescence by plumbagin. The binding constant obtained by fluorescence spectroscopy was of the similar order as in case of UV-vis spectroscopy. The negative value of Delta H degrees (-3.67) indicated an endothermic nature of the reaction and negative value of Delta G degrees (-6.40 to -6.58) confirmed that complexation of plumbagin to HSA was spontaneous. There was nearly one binding site in HSA for plumbagin. Titration of plumbagin to HSA in presence of site specific markers showed that plumbagin interacted at sub-domain IIA of HSA, commonly known as Sudlow's site I. Moreover, the binding resulted in changes in microenvironment of tryptophan while of tyrosine residues remained approximately unchanged. This interaction also resulted in decrease of alpha helical content of the studied serum protein. FRET calculations revealed that distance between plumbagin and HSA's fluorophore (Trp214) was 2.27 nm. Finally, molecular docking studies substantiated the in vitro finding. Plumbagin formed hydrogen bond with Lys199 and Arg257 of HSA. Additionally, Arg222, His242, and Ala261 interacted via van der Waals forces and Leu238, Leu260, Ile264, Ile290, and Ala291 of HSA interacted with plumbagin through hydrophobic forces. (C) 2020 The Author(s). Published by Elsevier B.V.