The nucleoporin Nup98 is a site for GDP/GTP exchange on Ran and termination of karyopherin β2-mediated nuclear import
The nucleoporin Nup98 is a site for GDP/GTP exchange on Ran and termination of karyopherin β2-mediated nuclear import
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DOI：
10.1074/jbc.m004651200
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发表时间：
2000-10-06
影响因子：
4.8
通讯作者：
Yaseen, NR
中科院分区：
文献类型：
--
作者：
Fontoura, BMA;Blobel, G;Yaseen, NR
核转运蛋白 β 2（Kap β 2，转运蛋白）结合人核糖核蛋白 A1 的 MS 序列并介导其入核。在这里，我们展示了核孔蛋白 Nup98 在核孔复合物 (NPC) 核侧 Kap beta 2 输入复合物的分解中的作用。 Kap beta 2 与 Nup98 N 末端的一个区域结合，该区域包含 MS 样序列。人核糖核蛋白A1 MS序列与Nup98竞争结合Kapβ2，表明Nup98可以将Kappa与其底物解离。 Kap beta 2 与 Nup98 的结合被负载有亚氨基磷酸鸟苷的 Ran 抑制，表明 RanGTP 将 Kappa 与 Nup98 解离，RanGTP 是通过 RanGEF (RCC1) 介导的核苷酸交换从 RanGDP 产生的。免疫电子显微镜和核苷酸交换测定显示 NPC 两侧都有功能性 RanGEF。在核方面，RanGEF 的定位与 Nup98 的定位一致。 RanGEF 在邻近 Kappa 结合位点的区域与 Nup98 结合。这些发现提出了一个模型，其中 1) 通过与 Nup98 MS 样位点竞争，从 NPC 核质侧的 Kap beta 2 释放输入底物，2) Nup98 结合的 RanGEF 催化 RanGTP 的形成，3) RanGTP 将 Kappa 从 Nup98 上解离，从而允许重复的输入循环。
Karyopherin beta 2 (Kap beta 2, transportin) binds the MS sequence of human ribonucleoprotein Al and mediates its nuclear import. Here we show a role for the nucleoporin Nup98 in the disassembly of Kap beta 2 import complexes at the nuclear side of the nuclear pore complex (NPC). Kap beta 2 bound to a region at the N terminus of Nup98 that contains an MS-like sequence. The human ribonucleoprotein Al MS sequence competed with Nup98 for binding to Kap beta 2, indicating that Nup98 can dissociate Kappa from its substrate. Binding of Kap beta 2 to Nup98 was inhibited by Ran loaded with guanylyl imidophosphate, suggesting that RanGTP dissociates Kappa from Nup98, RanGTP is produced from RanGDP through nucleotide exchange mediated by RanGEF (RCC1). Immunoelectron microscopy and nucleotide exchange assays revealed functional RanGEF on both sides of the NPC. On the nuclear side, the localization of RanGEF coincided with that of Nup98. RanGEF bound to Nup98 at a region adjacent to the Kappa-binding site. These findings suggest a model where 1) import substrate is released from Kap beta 2 at the nucleoplasmic side of the NPC by competition with the Nup98 MS-like site, 2) Nup98-bound RanGEF catalyzes the formation of RanGTP, and 3) RanGTP dissociates Kappa from Nup98 allowing repeated cycles of import.