Insight into the binding of PEG-400 with eye protein alpha-crystallin: Multi spectroscopic and computational approach: possible therapeutics targeting eye diseases

Abstract

Alpha-crystallin (α-crystallin) is an important eye protein having chaperone activity; its aggregation and precipitation are vital in cataract development. Polyethylene glycol-400 (PEG-400) is an important constituent of eye drops and artificial tears. The present study was targeted to study the binding of α-crystallin and PEG-400 employing multi spectroscopy, isothermal titration calorimetry (ITC) along with molecular modeling and docking approach. There was an apparent hypochromism in α-crystallin in the presence of varying PEG-400 concentrations; the binding constant obtained was 0.9 X 105 M−1 implying that strong binding is taking place between α-crystallin and PEG-400. Fluorescence spectroscopy suggested good binding of PEG-400 to α-crystallin with a binding constant (K) of 106 M−1. Moreover, fluorescence quenching studies carried out at three different temperatures suggested α-crystallin-PEG-400 complex formation to be guided by combination of static and dynamic modes. Thermodynamic parameters suggested α-crystallin-PEG-400 complex formation is driven by van der Waals forces and hydrogen bonding, making it seemingly specific. Far UV-CD spectra revealed no shift in the peak implying no alterations in the secondary structure of α-crystallin upon PEG-400 binding further validating complex formation. In vitro assays were further entrenched by in silico assays. Molecular modeling was used to make the functionally active form of α-crystallin. A binding pocket located in the β chain was delineated by Prank Web; molecular docking showed binding of PEG-400 in this pocket. This study will give an insight into the binding of PEG-400 with α-crystallin and can serve as a rationale for the discovery of therapeutic molecules that can be used for the treatment of eye-related crystallin-directed diseases. Highlights PEG-400 is a constituent of lubricant eye drops. Molecular modelling gave functionally active crystallin. Molecular docking showed PEG-400 in the binding pocket. Fluorescence binding revealed good bindingα-crystallin and PEG400. The α-crystallin-PEG-400 complex was guided by static and dynamic quenching. Communicated by Ramaswamy H. Sarma