Skouri-Panet F, Bonneté F, Prat K, Bateman O A, Lubsen N H, Tardieu A
Laboratoire de Minéralogie-Cristallographie, CNRS-Universités Paris VI & VII, France.
Biophys Chem. 2001 Jan 31;89(1):65-76. doi: 10.1016/s0301-4622(00)00216-7.
Among lens crystallins, gamma-crystallins are particularly sensitive to oxidation, because of their high amount of Cys and Met residues. They have the reputation to induce, upon ageing, lens structural modifications leading to opacities. A combination of small angle X-ray scattering and chromatography was used to study the oxidation of gamma-crystallins. At pH 7.0, all the gamma-crystallins under study were checked to have the same structure in solution. Under gentle oxidation conditions at pH 8.0, human gammaS (hgammaS) and bovine gammaS (bgammaS) formed disulfide-linked dimers, whereas the other bgamma-crystallins did not. Cys20 was shown to be responsible for dimer formation since the C20S mutant only formed monomers. The hgammaS dimers were stable for weeks and did not form higher oligomers. In contrast, monomeric gammaS-crystallins freshly prepared at pH 8.0, and submitted to more drastic oxidation by X-ray induced free radicals, were rapidly transformed into higher oligomers. So, only extensive oxidation causing partial unfolding could be detrimental to the lens and linked to cataract formation. The gammaS-crystallins lack the temperature-induced opacification observed with the other gamma-crystallins and known as cold cataract. The oxidation-induced associative behaviour and cold cataract are therefore demonstrated to be uncoupled.
在晶状体晶状体蛋白中，γ-晶状体蛋白对氧化特别敏感，因为它们含有大量的半胱氨酸（Cys）和甲硫氨酸（Met）残基。随着年龄增长，它们会引发晶状体结构改变并导致混浊，因而声名在外。利用小角X射线散射和色谱联用技术研究γ-晶状体蛋白的氧化过程。在pH 7.0条件下，所有被研究的γ-晶状体蛋白在溶液中具有相同的结构。在pH 8.0的温和氧化条件下，人γS（hγS）和牛γS（bγS）形成了二硫键连接的二聚体，而其他牛γ-晶状体蛋白则没有。已证明半胱氨酸20（Cys20）是二聚体形成的原因，因为C20S突变体只形成单体。hγS二聚体在数周内保持稳定，不会形成更高的寡聚体。相比之下，在pH 8.0条件下新制备的单体γS-晶状体蛋白，经X射线诱导自由基进行更剧烈的氧化后，会迅速转化为更高的寡聚体。因此，只有导致部分解折叠的广泛氧化才可能对晶状体有害并与白内障形成有关。γS-晶状体蛋白缺乏其他γ-晶状体蛋白所具有的温度诱导混浊现象，即所谓的冷性白内障。因此，氧化诱导的缔合行为和冷性白内障被证明是不相关的。
