Analyzing Structure, Chaperone Activity and Aggregation of Human αB-Crystallin in the Presence of Copper Ions and Glutathione

α-crystallin is a member of small heat shock protein family (sHSP) which shows both structural and chaperone functions. This protein plays important role in eye lens transparency and indicates protective function in the other tissues. The lenticular levels of copper ions significantly enhance in diabetic patients, aged and cataractous lenses. In eye lenses, the free copper ions induce ascorbic acid auto-oxidation, leading to formation of dehydroascorbic acid and other oxidative products as well as reactive oxygen species. The oxidized forms of ascorbic acid along with the reducing sugars enter into pathological reactions with the eye lens proteins, forming toxic advanced glycation end-products (AGEs). As one of the main components of eye lens antioxidant defense mechanism, glutathione could scavenge the copper ions, inhibiting the formation of reactive oxygen species in eye lenses. In the current study, the structural and functional properties of human αB-crystallin were assessed using different spectroscopic methods. In the presence of copper ions, αB-crystallin exhibited important alterations in both structure and chaperone activity which upturned in the presence of glutathione. Moreover, incubation of human αB-crystallin with copper resulted in significant increase in the protein oligomeric size distribution which largely prevented upon simultaneous incubation with glutathione. Overall, glutathione may scavenge free copper ions in the lenticular tissue, inhibiting their damaging effects on crystallin proteins and other redox-sensitive molecular targets such as ascorbic acid. Our results may introduce a new protective role for glutathione which is highly important in diabetic and aged lenses showing increased levels of copper ions.