Effect of Temperature and Ionic Strength on Structure and Chaperone Activity of Glycated and Non-Glycated Alpha-Crystallins

As major chaperone of eye lens, alpha-crystallin (&agr:-Crs) is responsible for the transparency and refractive power of this region by preventing denaturation and precipitation of other proteins. As shown previously, cataract formation was positively associated with high salt intake and the elevation of blood sugar level. Here the effect of both temperature and ionic strength were studied on structure and chaperoning function of glycated and non-glycated &agr:-Crs. While chaperone activity of these proteins was increased as function of temperature elevation, in the presence of sodium salt (0- 160 mM), it was significantly decreased. As shown by fluorescence and circular dicroism (CD) instruments, the salt induced structural alteration of &agr:-Crs was accompanied with the exposure of hydrophobic surfaces and a transition from alpha- helical to beta-sheet structures. Moreover, the structural alterations induced by the salt were more pronounced in the case of glycated &agr:-Crs compared to that of non-glycated protein counterpart. Overall this study shows the structural changes accompanied with lose of the chaperone activity of &agr:-Crs induced by sodium chloride. Consequently, the obtained results may provide new evidences for the relationship between high salt intakes and cataract disease induced particularly by prolonged hyperglycemia.