The RanBP2/RanGAP1*SUMO1/Ubc9 SUMO E3 ligase is a disassembly machine for Crm1-dependent nuclear export complexes.

Tobias Ritterhoff,Hrishikesh Das,Götz Hofhaus,Rasmus R Schröder,Frauke Melchior,Annette Flotho

doi:10.1038/ncomms11482

Abstract

Continuous cycles of nucleocytoplasmic transport require disassembly of transport receptor/Ran-GTP complexes in the cytoplasm. A basic disassembly mechanism in all eukaryotes depends on soluble RanGAP and RanBP1. In vertebrates, a significant fraction of RanGAP1 stably interacts with the nucleoporin RanBP2 at a binding site that is flanked by FG-repeats and Ran-binding domains, and overlaps with RanBP2's SUMO E3 ligase region. Here, we show that the RanBP2/RanGAP1*SUMO1/Ubc9 complex functions as an autonomous disassembly machine with a preference for the export receptor Crm1. We describe three in vitro reconstituted disassembly intermediates, which show binding of a Crm1 export complex via two FG-repeat patches, cargo-release by RanBP2's Ran-binding domains and retention of free Crm1 at RanBP2 after Ran-GTP hydrolysis. Intriguingly, all intermediates are compatible with SUMO E3 ligase activity, suggesting that the RanBP2/RanGAP1*SUMO1/Ubc9 complex may link Crm1- and SUMO-dependent functions.

Highlights

Directionality of nucleocytoplasmic transport is controlled by spatially separated assembly and disassembly of transport receptor/cargo complexes[1,2,3]
Here we show that the vertebrate RanBP2 complex, which is an NPC component in interphase and a soluble entity in mitosis, is an autonomous disassembly machine for prototypic Crm1-dependent export complexes (Fig. 6d)
Consistent with this, five of the six transport receptors tested here failed to interact with the RanBP2 complex in a stringent in-solution assay, Crm[1] being the striking exception

Summary

Introduction

Directionality of nucleocytoplasmic transport is controlled by spatially separated assembly and disassembly of transport receptor/cargo complexes[1,2,3] Key players in these pathways are nuclear import and export receptors of the importin b/karyopherin b-superfamily, the GTPase Ran and regulatory components of the Ran GTPase cycle. A basic disassembly-machinery, which is made up of soluble RanGAP and RanBP1, is conserved among all eukaryotes It is required for the disassembly of both trimeric export complexes and recycling import/Ran-GTP complexes. With its RanBDs and the associated RanGAP1*SUMO1, the RanBP2 complex contains the two elements that are required for disassembly of transport receptor/Ran-GTP complexes, and may represent an alternative to soluble RanGAP1 and RanBP1 with redundant, partially overlapping and/or with highly specific functions. These findings allow speculating that Crm1-dependent processes in interphase and/ or in mitosis are directly linked to RanBP2-dependent SUMOylation

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