Lee J S, Samejima T, Liao J H, Wu S H, Chiou S H
Department of Ophthalmology, Chang-Gung Memorial Hospital, Taipei, Taiwan.
Biochem Biophys Res Commun. 1998 Mar 17;244(2):379-83. doi: 10.1006/bbrc.1998.8272.
Previous reports on the chaperone activity of alpha-crystallin to prevent protein denaturation and thermal aggregation have suggested that partially denatured proteins can bind alpha-crystallin in its central region. Likewise, beta- and gamma-crystallin can also be localized to the central cavity of alpha-crystallin particle in vivo, which provides indirect evidence that alpha-crystallin can function as a chaperone in the intact lens. In this study, we have further demonstrated that the binding of the substrate proteins to alpha-crystallin by short-term preincubation may mimic the in vivo conditions of crystallin association. Preheating of alpha-crystallin with its substrate proteins at 60 degrees C for 20 min resulted in the formation of stable complexes between alpha-crystallin and its substrates (8.0% of insulin or 5.3% of gamma-crystallin was involved in complex formation). Under such conditions, the chaperone activity of alpha-crystallin to inhibit dithiothreitol-, ultraviolet-, or oxidation-induced protein aggregation can be greatly enhanced. Since UV-irradiation and oxidative stress are common insults to eye lenses under normal physiological conditions, the presence of alpha/gamma and alpha/beta complex in vivo may play an important role to maintain the lens in a transparent state.
先前关于α-晶状体蛋白防止蛋白质变性和热聚集的伴侣活性的报道表明，部分变性的蛋白质可以在其中心区域与α-晶状体蛋白结合。同样，β-和γ-晶状体蛋白在体内也可以定位于α-晶状体蛋白颗粒的中心腔，这提供了间接证据，表明α-晶状体蛋白在完整晶状体中可以发挥伴侣作用。在本研究中，我们进一步证明，通过短期预孵育使底物蛋白与α-晶状体蛋白结合，可能模拟了晶状体蛋白结合的体内条件。将α-晶状体蛋白与其底物蛋白在60℃下预热20分钟，导致α-晶状体蛋白与其底物之间形成稳定的复合物（8.0%的胰岛素或5.3%的γ-晶状体蛋白参与复合物形成）。在这种条件下，α-晶状体蛋白抑制二硫苏糖醇、紫外线或氧化诱导的蛋白质聚集的伴侣活性可以大大增强。由于紫外线照射和氧化应激是正常生理条件下眼晶状体常见的损伤因素，体内α/γ和α/β复合物的存在可能在维持晶状体透明状态方面发挥重要作用。
