Arginine Delays the Onset of Selenite–induced Cataract and Increases in vitro Chaperone–like Activity of Alpha Crystallin

Abstract

Abstract: : Purpose: We have shown earlier that temperature dependant structural perturbation of α–crystallin leads to enhancement of its chaperone–like activity. The purpose of the present study is to investigate the effect of arginine, a mild chaotrope, on the chaperone–like activity of α–crystallin in vitro and to investigate the effect of arginine administration on cataract formation in selenite–induced cataract model in rats. Methods: The effect of arginine on the chaperone–like activity of α–crystallin was studied using insulin aggregation as a model system. Changes in the accessibility of thiol group (present towards the end of α–crystallin domain) in the presence of arginine were studied using DTNB. The effect of arginine on the structural changes of α–crystallin was investigated by CD, fluorescence and glycerol density centrifugation. We have investigated changes in the dynamics of the subunit assembly by FRET and structural destabilization by urea–induced denaturation of α–crystallin in the presence of arginine. Results: Arginine increases the chaperone–like activity of αA–and αB–crystallin, the increase being more pronounced for αB–crystallin. Our study shows subtle changes in tertiary structure and significant decrease in the oligomeric size of α–crystallin in the presence of arginine. The extent and rate of thiol–group accessibility are increased in the presence of arginine. Increased exposure of hydrophobic surfaces of α–crystallin in the presence of arginine is observed by pyrene–solubilization and ANS–binding studies. Arginine increases the susceptibility of α–crystallin to urea–induced denaturation and increases subunit exchange between the oligomers of α–crystallin. Animal experiments show that administration of arginine significantly delays the onset of cataract in rats. Conclusions: Our studies show that arginine perturbs tertiary structure of α–crystallin, decreases the oligomeric size, increases exposed hydrophobic surface, enhances subunit exchange, and thus, enhances its chaperone–like activity. Arginine administration results in delaying the onset of cataract, without any toxic effects in the concentration range used for this study. Further investigations should show if this enhanced activity in vitro is associated with the observed in vivo protection.

Keywords: cataract • crystallins • chaperones