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Structure of importin-β bound to the IBB domain of importin-α

Nature volume 399, pages 221–229 (1999)Cite this article

Abstract

Cytosolic proteins bearing a classical nuclear localization signal enter the nucleus bound to a heterodimer of importin-α and importin-β (also called karyopherin-α and -β). The formation of this heterodimer involves the importin-β-binding (IBB) domain of importin-α, a highly basic amino-terminal region of roughly 40 amino-acid residues. Here we report the crystal structure of human importin-β bound to the IBB domain of importin-α, determined at 2.5 Å and 2.3 Å resolution in two crystal forms. Importin-β consists of 19 tandemly repeated HEAT motifs and wraps intimately around the IBB domain. The association involves two separate regions of importin-β, recognizing structurally distinct parts of the IBB domain: an amino-terminal extended moiety and a carboxy-terminal helix. The structure indicates that significant conformational changes occur when importin-β binds or releases the IBB domain domain and suggests how dissociation of the importin-α/β heterodimer may be achieved upon nuclear entry.

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Figure 1: Structure of importin-β bound to the IBB domain of importin-α.
Figure 2: Primary and secondary structures of importin-β and the IBB domain.
Figure 3: Recognition of the IBB domain by importin-β.
Figure 4: Comparison of the complex in two crystal forms.
Figure 5: A comparison of importins α and β.

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Acknowledgements

We thank M. Moulin for excellent technical assistance; R. W. Frank at the Zentrum für Molekulare Biologie, Universität Heidelberg for peptide synthesis; members of the EMBL/ESRF Joint Structural Biology Group, in particular G. Leonard and A. Thompson for access and support at beamline BM14, W.Burmeister at beamline ID14-3 and J. Lescar and B. Rasmussen at beamline ID02; and D.Barford for providing us with the coordinates of the PR65/A subunit of PP2A before release. We acknowledge our use of the HKL package as part of a collaboration with Z. Otwinowski and W. Minor, supported by the NIH. C.P. was supported by an EMBO fellowship and by a Marie Curie (TMR) fellowship.

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Authors and Affiliations

  1. European Molecular Biology Laboratory (EMBL), Grenoble Outstation c/o ILL BP 156, Grenoble, 38042 Cedex 9, France

    Gino Cingolani, Carlo Petosa & Christoph W. Müller

  2. University of California, Berkeley

    Karsten Weis

  3. Department of Molecular & Cell Biology, Berkeley, 94720–3200, California, USA

    Karsten Weis

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Correspondence to Christoph W. Müller.

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Cingolani, G., Petosa, C., Weis, K. et al. Structure of importin-β bound to the IBB domain of importin-α . Nature 399, 221–229 (1999). https://doi.org/10.1038/20367

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