Explication of human γD-crystallin interactions with its aggregation inhibitor schiff base at molecular level

Abstract Cu(II)-induced aggregation of human γD-crystallin (HGD) was reported to be inhibited by a Schiff base (SB). In this work, interactions between HGD and its aggregation inhibitor were probed by using different fluorescence based techniques, circular dichroism and molecular docking. Ground-state complexation between HGD and SB caused fluorescence quenching of tryptophan residues of HGD. Thermodynamic parameters suggest the involvement of hydrogen bonding and/or van der Waals interactions between the complexing species. From FRET, donor (tryptophan of HGD) to acceptor (SB) distance was calculated as 3.56 nm. Complexation of SB with HGD did not result any conformational alteration as confirmed by the synchronous fluorescence and CD spectroscopy. Molecular docking envisaged binding of SB in the C-terminal domain of HGD, which is presumably associated with the process of aggregation. Therefore, in addition to the reduction of free Cu(II) concentration in lens by virtue of the chelation ability of the Schiff base, the binding of the inhibitor with HGD can also inhibit its aggregation.