Structure of the exportin Xpo4 in complex with RanGTP and the hypusine-containing translation factor eIF5A.

Metin Aksu,Dirk Görlich,Sergei Trakhanov

doi:10.1038/ncomms11952

Metin Aksu, Dirk Görlich + Show 1 more

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https://doi.org/10.1038/ncomms11952

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Abstract

Xpo4 is a bidirectional nuclear transport receptor that mediates nuclear export of eIF5A and Smad3 as well as import of Sox2 and SRY. How Xpo4 recognizes such a variety of cargoes is as yet unknown. Here we present the crystal structure of the RanGTP·Xpo4·eIF5A export complex at 3.2 Å resolution. Xpo4 has a similar structure as CRM1, but the NES-binding site is occluded, and a new interaction site evolved that recognizes both globular domains of eIF5A. eIF5A contains hypusine, a unique amino acid with two positive charges, which is essential for cell viability and eIF5A function in translation. The hypusine docks into a deep, acidic pocket of Xpo4 and is thus a critical element of eIF5A's complex export signature. This further suggests that Xpo4 recognizes other cargoes differently, and illustrates how Xpo4 suppresses – in a chaperone-like manner – undesired interactions of eIF5A inside nuclei.

Highlights

Xpo[4] is a bidirectional nuclear transport receptor that mediates nuclear export of eIF5A and Smad[3] as well as import of Sox[2] and SRY
The nuclear membranes separate nucleus from cytoplasm, and force nucleocytoplasmic exchange to proceed through nuclear pore complexes (NPCs; reviewed in refs 2,3)
The importin molecule returns to the cytoplasm, where the RanGTP ligand is removed by a multi-step reaction that involves GTP-hydrolysis and loading of another cargo molecule

Summary

Results

It left eIF5A and Ran intact, but cleaved Xpo[4] within two poorly conserved loops comprising residues 241–260 and 931–948, respectively (Fig. 1c and Supplementary Fig. 1) Deleting these loops led to an Xpo[4] mutant that still bound Ran and eIF5A like the wild-type exportin (Fig. 1d,e), but became trypsin-resistant (Fig. 1f) and yielded triclinic export complex crystals even without protease addition. The superhelical arrangement of Xpo[4] is interrupted by three anticlockwise kinks (between HEATs 3 and 4, HEATs 9 and 10, and HEATs 13 and 14) that bend the superhelical structure into a toroid-like shape, whereby HEAT 20 touches the loop between HEATs 2 and 3 This architecture is very similar to the cargo-bound form of CRM1 (refs 21,22; see below, Fig. 4), a difference being that Xpo[4] lacks the most C-terminal helix of CRM1.

H12 W693 S694 S695 E696

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Methods