Quantification of anti-aggregation activity of UV-irradiated α-crystallin

Ultraviolet radiation is a risk factor for cataractogenesis. It is believed that enhanced rates of lens opacification and cataract formation are the results of gradual loss of chaperone-like efficiency of α-crystallin upon exposure to UV light. To characterize chaperone-like activity of α-crystallin damaged by UV irradiation, a test system based on dithiothreitol-induced aggregation of holo-α-lactalbumin from bovine milk was used. The adsorption capacity of α-crystallin (AC0) with respect to the target protein (α-lactalbumin) was used as a measure of anti-aggregation activity of α-crystallin. The data on SDS-PAGE testify that UV irradiation of α-crystallin results in covalent cross-linking of subunits in α-crystallin oligomers. The dependence of AC0 value on the irradiation dose was compared with the UV-induced diminution of the portion of native α-crystallin estimated from the data on differential scanning calorimetry. On the basis of such comparison a conclusion has been made that the loss in chaperone-like activity is mainly due to UV-induced denaturation of α-crystallin subunits. Cross-linking of remaining native subunits leads to an additional decrease in anti-aggregation activity.