Ran-dependent docking of importin-β to RanBP2/Nup358 filaments is essential for protein import and cell viability

Abstract

RanBP2 captures RanGTP–importin-β complexes at cytoplasmic fibrils to ensure adequate classical NLS–mediated protein import and cell viability.

Nuclear pore complex tethers to the cytoskeleton

“…Interestingly, SUMO isopeptidases, such as SENP2, which cleave SUMO from the substrate are located at the nucleoplasmic face of the NPC (Zhang et al, 2002), suggesting a role for SUMOylation in the directionality of nucleo-cytoplasmic transport. Therefore, Nup358 is important for the translocation of molecules through the NPC (Singh et al, 1999;Hutten et al, 2008;Wälde et al, 2012;Hamada et al, 2011;Forler et al, 2004;Mahadevan et al, 2013).…”

“…3). It is a large (358 KD), flexible, 36 nm long (Delphin et al, 1997) protein, shown by crosslinking mass spectrometry to be anchored by its N-terminus (Hamada et al, 2011) to two components (Nup133 and Nup96) of the so-called Y-complex (Kosinski et al, 2016), which constitute the scaffolding rings of the core of the NPC. The stable localization of Nup358 to the NPC may also be dependent of Nup214 and Nup88, shown by RNAi experiments in HeLa cells (Bernad et al, 2004), although immunodepletion of Nup214 from an in vitro nuclear reassembly assay showed that Nup214 was not essential for Nup358 localization (Walther et al, 2002).…”

The RanBP2/RanGAP1*SUMO1/Ubc9 complex

“…While a direct involvement of RanBP2's E3 ligase region in nucleocytoplasmic transport has not yet been demonstrated, it has been found to be important in mitosis: both known SUMO targets of RanBP2, Topoisomerase 2 α and Borealin, are sumoylated in mitosis, 12,16 and the E3 ligase region of RanBP2 is sufficient to alleviate chromosome segregation defects observed upon RanBP2 depletion 13 that have been linked to Topoisomerase 2 α sumoylation. 12 Interestingly, a fraction of the RanBP2/RanGAP1*SUMO1/ Ubc9 complex localizes to kinetochores in dependence of Crm1 and RanGTP, 29 raising the possibility that associations with export-like complexes may tether the E3 ligase complex at kinetochores.…”

“…25 and references therein). While RanBP2's most essential transport functions have been mapped to the N-terminal half of the protein excluding the E3 ligase region, 13,26 RanBP2-associated RanGAP1 has been found to be important for the What Makes the RanBP2/ RanGAP1*SUMO1/Ubc9 Complex So Fascinating?…”

“…RanBP2 is an essential protein playing a role in various cellular processes, but only some of its functions have been linked to its SUMO ligase activity. [11][12][13] The region in RanBP2 responsible for E3 ligase activity is contained within a C-terminal region harboring two 50 amino acid internal repeats (IR1 and IR2) separated by a 20 amino acid linker. Both repeats can interact with the E2 conjugating enzyme Ubc9, although with different affinities.…”