Molecular Structure and Function of Crystallins

在人类和动物模型中，伽马晶体蛋白都与白内障有关。它们也可能在其他眼睛组织中扮演与压力相关的角色，特别是视网膜。我们已经证明，它们可以在稳定晶状体中的细胞骨架方面发挥作用。 G-晶体蛋白具有非常不寻常的溶液性质，适合于高蛋白浓度环境。它们具有稳定、紧密折叠的结构，但可以展开形成淀粉样纤维。我们已经研究了鸟类和哺乳动物GS-晶体蛋白家族成员的展开/再折叠。 我们在许多g-晶体蛋白中发现了一种意想不到的二聚化模式，这种模式与分子偶极的大小和方向有关。与我们的合作者的AUC数据显示，GS-晶体蛋白确实在高浓度下发生二聚化，类似于在晶状体中发现的那些。 我们还在研究氧化和其他压力如何有助于晶体蛋白的展开和聚集，我们现在有了氧化条件下小鼠GS变体的晶体结构。这种显著的结构似乎是一种聚集中间产物，涉及分子内和分子间的S-S键、应变区交换和二级结构的渐进性丧失。这增加了对导致白内障的过程的重要洞察力。进一步的实验表明，晶体中的八聚体结构是通过二硫键连接的四聚体形成的，但这种几何结构不允许形成完全的二硫键。 使用圆二色谱和其他技术的其他实验表明，多聚化先于二硫化物的形成和二级结构的丧失。这表明聚集过程中组织结构的丧失被加强，提示在白内障中存在级联效应。

gamma-Crystallins are associated with cataract in both human and animal models. They may also have stress related roles in other eye tissues, notably retina. We have shown that they can play a role in stabilization of cytoskeleton in lens. g-Crystallins have highly unusual solution properties that fit them for high protein concentration environments. They have stable, tightly folded structures but can unfold to form amyloid like fibrils. We have studied unfolding/refolding in members of the gS-crystallin family from birds and mammals. We have identified an unexpected mode of dimerization in many g-crystallins that correlates with the magnitude and direction of molecular dipoles. AUC data with our collaborators show that gS-crystallins do dimerize at high concentrations similar to those found in the lens. We are also investigating how oxidation and other stresses contribute to crystallin unfolding and aggregation, We now have a crystal structure for a variant of mouse gS under oxidizing conditions. This remarkable structure appears to be an aggregation intermediate involving intra- and inter-molecular S-S bonds, strained domain swapping and progressive loss of secondary structure. This adds important insight into the processes that lead to cataract. Further experiments show that the octameric structure in the crystal forms by dimerization of a disulfide linked tetramer but that geometry does not allow full disulfide formation. Additional experiments using circular dichroism and other techniques suggest that multimerization precedes disulfide formation and loss of secondary structure. This shows that the loss of organized structure is enhanced by the processes of aggregation, suggesting a cascade effect in cataract.