Elucidation of molecular interactions between human γD-crystallin and quercetin, an inhibitor against tryptophan oxidation

Abstract

Different post-translational changes in eye lens crystallin proteins contribute towards the development of cataract. We have studied in vitro oxidative modification of tryptophan (Trp) residues of human γD-crystallin (HGD) towards formation of N-formylkynurenine (NFK) associated with cataractogenesis. This oxidation was found to be inhibited by quercetin at relatively low concentration. Interactions between quercetin and HGD were further studied using fluorescence techniques. Binding and quenching constants were determined as ∼10⁴ M⁻¹. Static quenching of fluorescence due to HGD–quercetin complex formation at ground state was confirmed by finding excited state life time of Trp residues. Energy transfer occurred between the protein and quercetin. Hydrogen bonding and/or van der Waals interactions were involved between HGD and quercetin. Synchronous and three-dimensional fluorescence along with far-UV CD studies suggested no major conformational alterations occurred in HGD due to quercetin binding. Experimental observations were supported by the docking results.

Communicated by Ramaswamy H. Sarma

Keywords:

• Human γD-crystallin
• oxidative damage of tryptophan
• inhibition by quercetin
• fluorescence quenching
• three-dimensional fluorescence

Acknowledgments

K.S.G. and S.R. are grateful to the Director, NIT Hamirpur for providing the research facilities. K.S.G. is thankful to Prof. D. Balasubramanian, L.V. Prasad Eye Hospital, Hyderabad for his kind gift of HGD clone. S.R. and K.S.G. gratefully acknowledge some instrumental assistance received from Dr. Anjan Chakraborty, IIT Indore and Dr. Rajanish Giri, IIT Mandi.

Disclosure statement

No potential conflict of interest was reported by the author(s).