Alteration of dynamic quaternary structure and calcium-binding ability of β-crystallin by light

Abstract

β-crystallin, one of the three main constituent proteins of the eye lens, exists as an equilibrium population of oligomeric (βH), trimeric (βL1) and dimeric (βL2) 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 β-crystallin, using size-exclusion chromatography. Irradiation of a solution of βH-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 βL2 solution for 30 min does not perturb the elution profile, while irradiation for a longer time increases the content of βL1 (trimeric) crystallin. Irradiation also causes a decrease in the calcium-binding affinity of the β-crystallins.