The small heat-shock protein, αB-crystallin, has a variable quaternary structure
The small heat-shock protein, αB-crystallin, has a variable quaternary structure
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DOI：
10.1006/jmbi.1997.1611
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发表时间：
1998-03-20
影响因子：
5.6
通讯作者：
Stewart, PL
中科院分区：
文献类型：
--
作者：
Haley, DA;Horwitz, J;Stewart, PL
α B-晶状体蛋白是透镜中的主要结构蛋白，其存在于多种其它组织中，并且与许多神经障碍有关。它是一个小的热休克蛋白家族的成员，并具有分子伴侣样的性质，冷冻电子显微镜已被应用于分析的四级结构的人重组α B-晶体蛋白，自发地形成约球形多聚体的直径为8至18 nm。基于近5000个α B-晶状体蛋白颗粒的类和图像揭示了蛋白质壳内存在大的中心腔、密度弱的区域和不对称的四级结构。类和图像在大小和形状上是可变的，并且暗示构象柔性组装的快照。由于鳗鱼过滤色谱法揭示了组装体的分子量范围（650（+/-140）kDa），因此基于总分子量对类和图像进行了进一步分类。从分配给32个亚基（类似于645 kDa）组装体的图像计算类似于4 nm分辨率的重建。类和图像与重建的重投影的比较表明，分辨率是有限的组件的可变性质。三维方差图表明蛋白质壳内和颗粒外表面上存在显著的结构差异。一些强变化可能对应于α B-晶状体蛋白单体的柔性暴露的C-末端残基。α B-晶状体蛋白的可变四级结构与组装体的多分散尺寸和先前观察到的多聚体之间的亚基交换一致。因此，我们建议，单体包装是可变的，组装的四级结构是不完全确定的。可变的α B-晶状体蛋白四级结构可以促进靶蛋白以高达化学计量比的结合。(C)出版社：Academic Press Limited。
alpha B-crystallin is a major structural protein in the lens that is found in a variety of other tissues and is associated with numerous neurological disorders. It is a member of the small heat-shock protein family and possesses chaperone-like properties, Cryo-electron microscopy has been applied to analyze the quaternary structure of human recombinant alpha B-crystallin, which spontaneously forms roughly spherical multimers 8 to 18 nm in diameter. Class-sum images based on nearly 5000 alpha B-crystallin particles reveal the presence of a large central cavity, weak regions of density within the protein shell, and an asymmetric quaternary structure. The class-sum images are variable in size and shape, and are suggestive of snapshots of a conformationally flexible assembly. As,eel-filtration chromatography reveals a range of molecular masses (650 (+/-140) kDa) for the assembly, the class-sum images were further classified on the basis of total molecular mass. A reconstruction at similar to 4 nm resolution was calculated from the images assigned to 32 subunit (similar to 645 kDa) assemblies. Comparison of class-sum images with reprojections of the reconstruction indicates that the resolution is limited by the variable nature of the assembly. A three-dimensional variance map indicates significant structural divergence within the protein shell and on the outer surface of the particle. Some of the strong variance may correspond to the flexible, exposed C-terminal residues of the alpha B-crystallin monomers. The variable quaternary structure of alpha B-crystallin is consistent with the polydisperse size of the assembly and the previously observed subunit exchange between multimers. Thus, we propose that the monomer packing is variable, and that the quaternary structure of the assembly is not completely defined. A variable alpha B-crystallin quaternary structure may facilitate binding of target proteins in up to stoichiometric ratios. (C) 1998 Academic Press Limited.