Correlation Between the Loss of the Chaperone-like Activity and the Oxidation, Isomerization and Racemization of Gamma-irradiated Alpha-crystallin¶

Abstract Alpha- crystallinpossesses a molecular chaperone-like activity that prevents proteins from aggregating; however, the mechanism of this activity is not well known. Here we have taken gamma-irradiated alpha- crystallinand studied the relationship between the decrease in chaperone-like activity and the modifications such as oxidation, isomerization and racemization of amino acids in this molecule. We found that the chaperone-like activity of alpha- crystallindecreased with increasing gamma irradiation. After 4000 Gy gamma irradiation the activity of alpha- crystallinwas reduced to 40% of the level of nonirradiated, native alpha- crystallin. The circular dichroism spectrum showed that the secondary structure of the irradiated alpha- crystallinhad not changed. However, its tertiary structure appeared to change following more than 1000 Gy irradiation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis also indicated that cross-linking of alpha- crystallinincreased with increasing radiation doses....