Tyrosine mediated conformational change in bone morphogenetic protein – 2: Biophysical implications of protein – phytoestrogen interaction

Abstract

The biophysical aspects of the binding interaction between a phytoestrogen (quercetin, QT) and bone morphogenetic protein – 2 (BMP – 2) was analyzed by various spectroscopic, calorimetric and molecular docking techniques. Interaction studies represented a loss in the absorbance of protein (only the amide region) along with a prominent red shift indicating ground-state complexation which was further confirmed by quenching with significant blue shift observed from steady-state fluorescence measurements. To narrow down the involvement of aromatic residues (Tyr & Trp), synchronous fluorescence spectroscopy was employed. Both Tyr and Trp fluorescence intensity was quenched, however, shifting was noticed only in case of Tyr residues; thus, confirming the alteration in confirmation was mediated upon reduction in polarity around tyrosine residues. It was further validated by quenching studies which highlighted the existence of a buried fraction of fluorophore upon interaction. The nature of fluorescence quenching was static and the binding efficiency was low (binding constant K ~ 10−2 M). Mechanistically, the involvement of van der Waals and hydrogen bonding interaction was confirmed from both van't Hoff plot and molecular docking studies. Secondary structure and thermal stability of the protein was not significantly affected by quercetin. All these investigations confirmed a significant effect on the structure and conformation of BMP – 2 in presence of quercetin which might serve as a potential therapeutic for the treatment of osteoporosis in postmenopausal women.