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Effect of the UV Modification of α‐Crystallin on Its Ability to Suppress Nonspecific Aggregation
Author(s) -
Ellozy Aziza R.,
Ceger Patricia,
Wang Ren H.,
Dillon James
Publication year - 1996
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1996.tb02469.x
Subject(s) - crystallin , irradiation , denaturation (fissile materials) , chemistry , biophysics , kinetics , chromophore , protein aggregation , chaperone (clinical) , photochemistry , biochemistry , nuclear chemistry , biology , medicine , physics , pathology , quantum mechanics , nuclear physics
Recent studies have shown that structural modifications of α‐crystallin during lens aging decrease it's effectiveness as a molecular chaperone. Some of these posttranslational modifications have been linked to UV radiation, and this study was undertaken to investigate the effect of UV irradiation on the ability of α‐crystallin to suppress nonspecific aggregation. The effect of 3‐hydroxykynurenine (3‐HK) was also investigated as a model for its glucoside (3‐HKG), a main lens chromophore that has been linked to photochemical changes in the human lens. Alpha‐ and γ‐crystallin solutions (1 mg/mL, 1:0.125 wt/wt) were photolyzed (transmission above 295 nm) for various time intervals. Thermal denaturation of γ‐crystallin with or without α‐crystallin was carried out at 70°C and increases in light scattering were measured at 360 nm. We found that (1) irradiation of γ‐crystallin increased its susceptibility to heat‐induced scattering. The addition of α‐crystallin protects it against thermal denaturation, although its ability to do so decreases the longer γ‐crystallin is irradiated and (2) irradiation of α‐crystallin decreases its ability to suppress nonspecific aggregation and the presence of 3‐HK during irradiation decreases it further. Our results indicate that posttranslational modifications of α‐crystallin due to UV irradiation affect the sites and mechanisms by which it interacts with γ‐crystallin. The kinetics of γ‐crystallin unfolding during thermal denaturation were also analyzed. We found that a simple two state model applies for nonirradiated γ‐crystallin. This model does not hold when γ‐crystallin is irradiated in the presence or absence of α‐crystallin. In these cases, two step or multistep mechanisms are more likely.