UV-B-induced secondary conformational changes in lens alpha-crystallin.

The changes in turbidity and protein secondary structure of alpha-crystallin after a 72 h UV-B (302 nm) irradiation in aqueous solution have been determined by UV spectrophotometry and Fourier transform infrared (FT-IR) microspectroscopy with reflection mode. The relative transmission of alpha-crystallin aqueous solution gradually decreases with the exposure time, indicating that the transparent alpha-crystallin aqueous solution becomes opaque with prolonged UV-B irradiation. The turbidity induced by UV-B shows first-order kinetics due to the photo-induced aggregation. The modification of the secondary structure of the alpha-crystallin molecule in aqueous solution caused by this aggregation might enhance the alpha-helix and beta-turn structures from 8.14 to 14.92% and from 24.46 to 35.54%, respectively; reduce the beta-sheet structure from 60.20% to 43.77%; and leave the random coil structure almost unaltered. The secondary conformation of alpha-crystallin changes gradually but evidently with its increase of turbidity during UV-B exposure.