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Structural basis for the assembly of a nuclear export complex

Abstract

The nuclear import and export of macromolecular cargoes through nuclear pore complexes is mediated primarily by carriers such as importin-β. Importins carry cargoes into the nucleus, whereas exportins carry cargoes to the cytoplasm. Transport is orchestrated by nuclear RanGTP, which dissociates cargoes from importins, but conversely is required for cargo binding to exportins. Here we present the 2.0 Å crystal structure of the nuclear export complex formed by exportin Cse1p complexed with its cargo (Kap60p) and RanGTP, thereby providing a structural framework for understanding nuclear protein export and the different functions of RanGTP in export and import. In the complex, Cse1p coils around both RanGTP and Kap60p, stabilizing the RanGTP-state and clamping the Kap60p importin-β-binding domain, ensuring that only cargo-free Kap60p is exported. Mutagenesis indicated that conformational changes in exportins couple cargo binding to high affinity for RanGTP, generating a spring-loaded molecule to facilitate disassembly of the export complex following GTP hydrolysis in the cytoplasm.

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Figure 1: Two orthogonal views, showing an overview of the structure of the Cse1p:Kap60p:RanGTP complex.
Figure 2: Role of the IBB domain in nuclear export complex formation.
Figure 3: Role of Ran in the export complex.
Figure 4: Mutations that influence the Cse1p:Kap60p:RanGTP complex.

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Acknowledgements

We thank the staff of the European Synchrotron Radiation Facility, especially D. Nurizzo and J. McCarthy, for assistance during data collection, and our colleagues in Cambridge, especially K. Nagai, R. Henderson, R.A. Crowther, P. Evans, A. Leslie and A. Stewart for comments, criticism and assistance. This work was supported in part by a Human Frontier Science Program grant.

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Correspondence to Murray Stewart.

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Supplementary information

Supplementary Figure S1

Arrangement of Cse1p HEAT repeats (JPG 168 kb)

Supplementary Figure S1 Legend (DOC 19 kb)

Supplementary Figure S2

Two orthogonal views of superimposition of importin-β, Kap-β2 and Cse1p bound to RanGTP. (JPG 87 kb)

Supplementary Figure S2 Legend (DOC 19 kb)

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Matsuura, Y., Stewart, M. Structural basis for the assembly of a nuclear export complex. Nature 432, 872–877 (2004). https://doi.org/10.1038/nature03144

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