ALTERATION OF DYNAMIC QUATERNARY STRUCTURE AND CALCIUM-BINDING ABILITY OF ß-CRYSTALLIN BY LIGHT

Abstract— ß-crystallin, one of the three main constituent proteins of the eye lens, exists as an equilibrium population of oligomeric (ßH), trimeric (ßL1) and dimeric (ßL2) species. This equlibrium is dependent on various factors such as the protein concentration, ionic strength and pH of the medium. WE have studied the effect of ultraviolet B radiation on the aggregational patterns of ß-crystallin, using size-exclusion chromatography. Irradiation of a solution of ßH-crystallin at 295 nm for about 30 min causes the deaggregation of the hexameric population into dimers. Irradiation for a longer time, however, produces cross-linked high molecular weight products. Irradiation of a ßL2 solution for 30 min does not perturb the elution profile, while irradiation for a longer time increases the content of ßL1 (trimeric) crystallin. Irradiation also causes a decrease in the calcium-binding affinity of the ß-crystallins.