Ellozy A R, Ceger P, Wang R H, Dillon J
Fordham University at Lincoln Center, New York, NY 10023, USA.
Photochem Photobiol. 1996 Aug;64(2):344-8. doi: 10.1111/j.1751-1097.1996.tb02469.x.
Recent studies have shown that structural modifications of alpha-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 alpha-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 gamma-crystallin solutions (1 mg/mL, 1:0.125 wt/wt) were photolyzed (transmission above 295 nm) for various time intervals. Thermal denaturation of gamma-crystallin with or without alpha-crystallin was carried out at 70 degrees C and increases in light scattering were measured at 360b nm. We found that (1) irradiation of gamma-crystallin increased its susceptibility to heat-induced scattering. The addition of alpha-crystallin protects it against thermal denaturation, although its ability to do so decreases the longer gamma-crystallin is irradiated and (2) irradiation of alpha-crystallin decreases its ability to suppress nonspecific aggregating and the presence of of 3-HK during irradiation decreases it further. Our results indicate that posttranslational modifications of alpha-crystallin due to UV irradiation affect the sites and mechanisms by which it interacts with gamma-crystallin. The kinetics of gamma-crystallin unfolding during thermal denaturation were also analyzed. We found that a simple two state model applies for nonirradiated gamma-crystallin. This model does not hold when gamma-crystallin is irradiated in the presence or absence of alpha-crystallin. In these cases, two step or multistep mechanisms are more likely.
最近的研究表明，晶状体老化过程中α-晶状体蛋白的结构修饰会降低其作为分子伴侣的有效性。其中一些翻译后修饰与紫外线辐射有关，本研究旨在探讨紫外线照射对α-晶状体蛋白抑制非特异性聚集能力的影响。还研究了3-羟基犬尿氨酸（3-HK）作为其糖苷（3-HKG）模型的作用，3-HKG是晶状体的主要发色团，与人类晶状体的光化学变化有关。将α-和γ-晶状体蛋白溶液（1 mg/mL，1:0.125 wt/wt）在不同时间间隔进行光解（295 nm以上的透射率）。在70℃下对有或无α-晶状体蛋白的γ-晶状体蛋白进行热变性，并在360b nm处测量光散射的增加。我们发现：（1）γ-晶状体蛋白的照射增加了其对热诱导散射的敏感性。添加α-晶状体蛋白可保护其免受热变性影响，尽管随着γ-晶状体蛋白照射时间的延长，其保护能力会降低；（2）α-晶状体蛋白的照射降低了其抑制非特异性聚集的能力，照射过程中3-HK的存在会进一步降低该能力。我们的结果表明，紫外线照射导致的α-晶状体蛋白翻译后修饰会影响其与γ-晶状体蛋白相互作用的位点和机制。还分析了热变性过程中γ-晶状体蛋白展开的动力学。我们发现，一个简单的两态模型适用于未照射的γ-晶状体蛋白。当γ-晶状体蛋白在有或无α-晶状体蛋白存在的情况下被照射时，该模型不成立。在这些情况下，更可能是两步或多步机制。
