Increased Sensitivity of Amino-arm Truncated ßA3 Crystallin to UV-light Induced Photo-aggregation

Abstract

Abstract: : Purpose: UV-B light is one of primary factors associated with cataract formation in the eye lens. ßγ-Crystallins maintain lens transparency and damage to these proteins plays a major role in cataract formation. ß-Crystallins tend to loose their terminal arms with lens aging. In order to analyze and compare the effects of UV-light on native and modified crystallins, UV-irradiation induced changes in purified recombinant wild type (rßA3) and amino-terminal truncated (rßA3tr) ßA3-crystallins were examined. Methods: Proteins were expressed in baculovirus-infected Sf9 cells and purified by a combination of ion exchange DEAE and size exclusion chromatography (SEC) on Superdex 75. Protein solutions (pH 7.4) were reduced using the disulphide bond breaker (Tris (2-carboxyethyl) phosphine HCl) and irradiated at physiologically relevant doses of UV-light at 20 ^oC using a 308 nm excimer laser, and transmittance (308 nm) and light scattering (633 nm) was measured. UV-Treated protein samples were characterized by protein absorption, SEC, SDS-PAGE and Western blots. Results: UV-Irradiation of both, rßA3 and rßA3tr, resulted in major loss of soluble protein shown by absorption at 280 nm, SEC and SDS-PAGE and formation of insoluble aggregates producing a subsequent light scattering. Although both proteins show a positive cooperative photo-kinetics with increasing UV-dose, the rßA3tr has a statistically significant tendency to begin scatter at lower UV-dose and has higher aggregation rate then rßA3. Conclusions: . The difference in UV-sensitivity of wild type and truncated ßA3-crystallins demonstrates that the loss of the terminal extension increases the tendency of rßA3tr to aggregate, suggesting the importance of truncated ß-crystallins for insoluble protein formation in lens and age-related cataract.

Keywords: crystallins • radiation damage: light/UV • cataract