Department of Biological Sciences, Crystallography, Institute of Structural and Molecular Biology, Birkbeck College, Malet Street, London WC1E 7HX, UK.
J Mol Biol. 2011 Apr 22;408(1):118-34. doi: 10.1016/j.jmb.2011.02.020. Epub 2011 Feb 15.
Small heat shock proteins form large cytosolic assemblies from an "α-crystallin domain" (ACD) flanked by sequence extensions. Mutation of a conserved arginine in the ACD of several human small heat shock protein family members causes many common inherited diseases of the lens and neuromuscular system. The mutation R120G in αB-crystallin causes myopathy, cardiomyopathy and cataract. We have solved the X-ray structure of the excised ACD dimer of human αB R120G close to physiological pH and compared it with several recently determined wild-type vertebrate ACD dimer structures. Wild-type excised ACD dimers have a deep groove at the interface floored by a flat extended "bottom sheet." Solid-state NMR studies of large assemblies of full-length αB-crystallin have shown that the groove is blocked in the ACD dimer by curvature of the bottom sheet. The crystal structure of R120G ACD dimer also reveals a closed groove, but here the bottom sheet is flat. Loss of Arg120 results in rearrangement of an extensive array of charged interactions across this interface. His83 and Asp80 on movable arches on either side of the interface close the groove by forming two new salt bridges. The residues involved in this extended set of ionic interactions are conserved in Hsp27, Hsp20, αA- and αB-crystallin sequences. They are not conserved in Hsp22, where mutation of the equivalent of Arg120 causes neuropathy. We speculate that the αB R120G mutation disturbs oligomer dynamics, causing the growth of large soluble oligomers that are toxic to cells by blocking essential processes.
小分子热休克蛋白通过“α-晶体蛋白结构域”（ACD）侧翼的序列延伸形成大的细胞溶质组装体。在几个人类小分子热休克蛋白家族成员的 ACD 中保守精氨酸的突变导致许多晶状体和神经肌肉系统的常见遗传性疾病。αB-晶体蛋白中的突变 R120G 导致肌病、心肌病和白内障。我们已经解决了接近生理 pH 的人 αB R120G 的切除 ACD 二聚体的 X 射线结构，并将其与最近确定的几种脊椎动物野生型 ACD 二聚体结构进行了比较。野生型切除 ACD 二聚体在界面上有一个深沟，由平坦的扩展“底部片”支撑。全长αB-晶体蛋白大组装体的固态 NMR 研究表明，在 ACD 二聚体中，底部片的曲率会阻塞沟。R120G ACD 二聚体的晶体结构也显示出一个封闭的沟，但这里的底部片是平的。Arg120 的缺失导致整个界面上的大量电荷相互作用的重新排列。界面两侧可移动拱上的 His83 和 Asp80 通过形成两个新的盐桥关闭沟。参与这个扩展的离子相互作用的残基在 Hsp27、Hsp20、αA-和αB-晶体蛋白序列中是保守的。在 Hsp22 中它们不保守，其中相当于 Arg120 的突变会导致神经病。我们推测，αB R120G 突变扰乱了寡聚体动力学，导致大的可溶性寡聚体的生长，这些寡聚体通过阻断基本过程对细胞有毒。
