Abteilung für Theoretische und Computergestützte Biophysik, Max-Planck-Institut für Biophysikalische Chemie, Am Faßberg 11, 37077 Göttingen, Germany.
Structure. 2013 Aug 6;21(8):1350-60. doi: 10.1016/j.str.2013.05.015. Epub 2013 Jul 11.
Proteins carrying nuclear export signals cooperatively assemble with the export factor CRM1 and the effector protein RanGTP. In lower eukaryotes, this cooperativity is coupled to CRM1 conformational changes; however, it is unknown if mammalian CRM1 maintains its compact conformation or shows similar structural flexibility. Here, combinations of small-angle X-ray solution scattering and electron microscopy experiments with molecular dynamics simulations reveal pronounced conformational flexibility in mammalian CRM1 and demonstrate that RanGTP binding induces association of its N- and C-terminal regions to form a toroid structure. The CRM1 toroid is stabilized mainly by local interactions between the terminal regions, rather than by global strain. The CRM1 acidic loop is key in transmitting the effect of this RanGTP-induced global conformational change to the NES-binding cleft by shifting its population to the open state, which displays enhanced cargo affinity. Cooperative CRM1 export complex assembly thus constitutes a highly dynamic process, encompassing an intricate interplay of global and local structural changes.
带有核输出信号的蛋白质与输出因子 CRM1 和效应蛋白 RanGTP 协同组装。在较低等真核生物中，这种协同作用与 CRM1 构象变化偶联；然而，尚不清楚哺乳动物 CRM1 是否保持其紧凑构象，还是表现出类似的结构灵活性。在这里，小角度 X 射线溶液散射和电子显微镜实验与分子动力学模拟的组合揭示了哺乳动物 CRM1 中明显的构象灵活性，并证明了 RanGTP 结合诱导其 N 端和 C 端区域的缔合形成环结构。CRM1 环主要通过末端区域之间的局部相互作用稳定，而不是通过全局应变。CRM1 酸性环是将这种 RanGTP 诱导的全局构象变化的影响传递到 NES 结合裂隙的关键，通过将其种群转移到开放状态，从而显示出增强的货物亲和力。因此，协同的 CRM1 输出复合物组装构成了一个高度动态的过程，包括全局和局部结构变化的复杂相互作用。
