Structural basis for cooperativity of CRM1 export complex formation
Structural basis for cooperativity of CRM1 export complex formation
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DOI：
10.1073/pnas.1215214110
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发表时间：
2013-01-15
影响因子：
11.1
通讯作者：
Ficner, Ralf
中科院分区：
文献类型：
--
作者：
Monecke, Thomas;Haselbach, David;Ficner, Ralf
在真核生物中，大分子的核质转运主要由核粘附素-β超家族中的可溶性核转运受体介导，这些受体被称为Importins和Exportins。高度通用的Exportin染色体区域维护1(CRM1)对于许多结构和功能无关的蛋白质和核糖核蛋白的核耗竭是必不可少的。CRM1已被证明在几种功能转运复合体中采用环状结构，并被认为在整个核质转运周期中保持这种构象。我们解析了嗜热真核生物热毛壳菌中游离CRM1的晶体结构。令人惊讶的是，未结合的CRM1显示出整体延伸和倾斜的超螺旋构象。与CRM1-RAN-SNurportin1三元出口复合体相比，两个调节区，即酸性环和C-末端a-螺旋，在游离CRM1中被戏剧性地重新定位。单粒子EM分析表明，在非晶态环境中，游离的CRM1在延伸的超螺旋构象和致密的环状构象之间处于平衡状态。分子动力学模拟表明，C端螺旋在调节从扩展构象到紧凑构象的转变中起着重要作用，并揭示了不同构象对货物核出口信号结合部位的影响。结合这些结果，我们提出了一个CRM1出口复合体组装的协同作用模型，该模型涉及GTP结合的RAN与货物之间的远程变构通讯。
In eukaryotes, the nucleocytoplasmic transport of macromolecules is mainly mediated by soluble nuclear transport receptors of the karyopherin-beta superfamily termed importins and exportins. The highly versatile exportin chromosome region maintenance 1 (CRM1) is essential for nuclear depletion of numerous structurally and functionally unrelated protein and ribonucleoprotein cargoes. CRM1 has been shown to adopt a toroidal structure in several functional transport complexes and was thought to maintain this conformation throughout the entire nucleocytoplasmic transport cycle. We solved crystal structures of free CRM1 from the thermophilic eukaryote Chaetomium thermophilum. Surprisingly, unbound CRM1 exhibits an overall extended and pitched superhelical conformation. The two regulatory regions, namely the acidic loop and the C-terminal a-helix, are dramatically repositioned in free CRM1 in comparison with the ternary CRM1-Ran-Snurportin1 export complex. Single-particle EM analysis demonstrates that, in a noncrystalline environment, free CRM1 exists in equilibrium between extended, superhelical and compact, ring-like conformations. Molecular dynamics simulations show that the C-terminal helix plays an important role in regulating the transition from an extended to a compact conformation and reveal how the binding site for nuclear export signals of cargoes is modulated by different CRM1 conformations. Combining these results, we propose a model for the cooperativity of CRM1 export complex assembly involving the long-range allosteric communication between the distant binding sites of GTP-bound Ran and cargo.