Kapinos Larisa E, Huang Binlu, Rencurel Chantal, Lim Roderick Y H
Biozentrum and the Swiss Nanoscience Institute, University of Basel, Basel, Switzerland.
Biozentrum and the Swiss Nanoscience Institute, University of Basel, Basel, Switzerland
J Cell Biol. 2017 Nov 6;216(11):3609-3624. doi: 10.1083/jcb.201702092. Epub 2017 Sep 1.
Nucleocytoplasmic transport is sustained by karyopherins (Kaps) and a Ran guanosine triphosphate (RanGTP) gradient that imports nuclear localization signal (NLS)-specific cargoes (NLS-cargoes) into the nucleus. However, how nuclear pore complex (NPC) barrier selectivity, Kap traffic, and NLS-cargo release are systematically linked and simultaneously regulated remains incoherent. In this study, we show that Kapα facilitates Kapβ1 turnover and occupancy at the NPC in a RanGTP-dependent manner that is directly coupled to NLS-cargo release and NPC barrier function. This is underpinned by the binding affinity of Kapβ1 to phenylalanine-glycine nucleoporins (FG Nups), which is comparable with RanGTP·Kapβ1, but stronger for Kapα·Kapβ1. On this basis, RanGTP is ineffective at releasing standalone Kapβ1 from NPCs. Depleting Kapα·Kapβ1 by RanGTP further abrogates NPC barrier function, whereas adding back Kapβ1 rescues it while Kapβ1 turnover softens it. Therefore, the FG Nups are necessary but insufficient for NPC barrier function. We conclude that Kaps constitute integral constituents of the NPC whose barrier, transport, and cargo release functionalities establish a continuum under a mechanism of Kap-centric control.
核质运输由核转运蛋白（Kaps）和Ran鸟苷三磷酸（RanGTP）梯度维持，该梯度将核定位信号（NLS）特异性货物（NLS-货物）导入细胞核。然而，核孔复合体（NPC）屏障选择性、转运蛋白运输和NLS-货物释放如何系统地联系并同时受到调控，目前仍不明确。在本研究中，我们表明转运蛋白α（Kapα）以RanGTP依赖的方式促进转运蛋白β1（Kapβ1）在NPC处的周转和占据，这直接与NLS-货物释放和NPC屏障功能相关。这是由Kapβ1与苯丙氨酸-甘氨酸核孔蛋白（FG Nups）的结合亲和力所支撑的，该亲和力与RanGTP·Kapβ1相当，但对Kapα·Kapβ1更强。在此基础上，RanGTP无法从NPC中释放单独的Kapβ1。通过RanGTP消耗Kapα·Kapβ1会进一步消除NPC屏障功能，而重新添加Kapβ1可挽救该功能，同时Kapβ1周转会使其减弱。因此，FG Nups对于NPC屏障功能是必要的，但并不充分。我们得出结论，转运蛋白是NPC的组成部分，其屏障、运输和货物释放功能在以转运蛋白为中心的控制机制下构成一个连续统一体。
