alpha A- and alpha B-crystallins protect glucose-6-phosphate dehydrogenaseagainst UVB irradiation-induced inactivation

alpha -Crystallin, a major eye lens protein, has been shown to function lik e a molecular chaperone by suppressing the aggregation of other proteins in duced by various stress conditions. Ultraviolet (UV) radiation is known to cause structural and functional alterations in the lens macromolecules. Ear lier we observed that exposure of rat lens to in vitro UV radiation led to inactivation of many lens enzymes including glucose-6-phosphate dehydrogena se (G6PD). In the present paper, we show that alpha -crystallin (alphaA and alphaB) protects G6PD from UVB irradiation induced inactivation. While, at 25 degreesC, there was a time-dependent decrease in G6PD activity upon irr adiation at 300 nm, at 40 degreesC there was a complete loss of activity wi thin 30 min even without irradiation. The loss of activity of G6PD was prev ented significantly, if alphaA- or alphaB-crystallin was present during irr adiation. At 25 degreesC, alphaB-crystallin was slightly a better chaperone in protecting G6PD against UVB inactivation, Interestingly, at 40 degreesC , alphaA- and alphaB-crystallins not only prevent the loss of G6PD activity but also protect against UVB inactivation, However, alphaA- and alphaB-cry stallins were equally efficient at 40 degreesC in protecting G6PD. (C) 2001 Academic Press.