alpha-Crystallin acting as a molecular chaperonin against photodamage by UV irradiation.

alpha-Crystallin, a major protein of the eye lens, is known to have chaperone activity in preventing heat-induced aggregation of enzymes and other crystallins. In this study, we investigate the ability of alpha-crystallin to inhibit UV-light-induced aggregation of other lens proteins and the effect of exposure of alpha-crystallin to UV irradiation on its chaperone activity. The chaperone activities of alpha-crystallin preincubated at different temperatures were found to be different and could be correlated with its change in quaternary structure as determined by the fluorescence probe ANS (8-anilo-1-naphthalene sulfonate). alpha-Crystallin can inhibit the aggregation of gamma-crystallin from UV irradiation at room temperature, and the preheated alpha-crystallins provide more protection than the native one. Upon irradiation by UV light, alpha-crystallin gradually lost its ability to protect beta-crystallin against thermal aggregation. The loss of the chaperone efficacy of alpha-crystallin to protect other lens proteins may shed light on human cataract formation induced by long-term exposure to UV irradiation.