PHYSIOLOGICAL-ROLE OF THE ASSOCIATION COMPLEXES OF ALPHA-CRYSTALLIN AND ITS SUBSTRATES ON THE CHAPERONE ACTIVITY

Previous reports on the chaperone activity of alpha-crystallin to prev ent protein denaturation and thermal aggregation have suggested that p artially denatured proteins can bind alpha-crystallin in its central r egion. Likewise, beta- and gamma-crystallin can also be localized to t he central cavity of alpha-crystallin particle in vivo, which provides indirect evidence that alpha-crystallin can function as a chaperone i n the intact lens. In this study, we have further demonstrated that th e binding of the substrate proteins to alpha-crystallin by short-term preincubation may mimic the in vivo conditions of crystallin associati on. Preheating of alpha-crystallin with its substrate proteins at 60 d egrees C for 20 min resulted in the formation of stable complexes betw een alpha-crystallin and its substrates (8.0% of insulin or 5.3% of ga mma-crystallin was involved in complex formation). Under such conditio ns, the chaperone activity of alpha-crystallin to inhibit dithiothreit ol-, ultraviolet-, or oxidation-induced protein aggregation can be gre atly enhanced. Since UV-irradiation and oxidative stress are common in sults to eye lenses under normal physiological conditions, the presenc e of alpha/gamma and alpha/beta complex in vivo may play an important role to maintain the lens in a transparent state. (C) 1998 Academic Pr ess.