Liang J N, Pelletier M R
Howe Laboratory of Ophthalmology, Massachusetts Eye and Ear Infirmary, Department of Ophthalmology, Harvard Medical School, Boston 02114.
Exp Eye Res. 1988 Jul;47(1):17-25. doi: 10.1016/0014-4835(88)90020-6.
Mixed disulfide between lens crystallin and glutathione has been observed in human cataracts and could be formed in vitro by thiol-disulfide exchange reaction. The glutathionyl crystallins have been reported to become partially unfolded. The present paper reports the conformational destabilization by the mixed disulfide formation in calf alpha- and gamma-II crystallin. The conformational stability was studied by the denaturants urea and guanidine hydrochloride (Gdn-HCl), and by proteolytic degradation. The denaturation curves of both urea and Gdn-HCl shift to lower denaturant concentration for crystallins of glutathione mixed disulfide. The decrease in conformational stability is estimated to be 0.22- and 0.92 kcal mol-1 for modified alpha- and gamma-II crystallin, respectively. Proteolytic digestion also shows a faster rate of degradation for the modified crystallins. These results indicate that mixed disulfide destabilizes the crystallin conformation. The destabilization may make crystallins more susceptible to changes as observed in aging lenses.
在人类白内障中已观察到晶状体晶状体蛋白与谷胱甘肽之间形成的混合二硫键，并且可以通过硫醇-二硫键交换反应在体外形成。据报道，谷胱甘肽化的晶状体蛋白会部分展开。本文报道了在小牛α-和γ-II晶状体蛋白中混合二硫键形成导致的构象不稳定。通过变性剂尿素和盐酸胍（Gdn-HCl）以及蛋白水解降解研究了构象稳定性。对于谷胱甘肽混合二硫键的晶状体蛋白，尿素和Gdn-HCl的变性曲线均向较低的变性剂浓度移动。经估算，修饰后的α-和γ-II晶状体蛋白的构象稳定性分别降低了0.22和0.92 kcal mol-1。蛋白水解消化也显示修饰后的晶状体蛋白降解速度更快。这些结果表明混合二硫键会使晶状体蛋白的构象不稳定。这种不稳定可能会使晶状体蛋白更容易发生如在老化晶状体中观察到的变化。
