Molecular basis for the recognition of a nonclassical nuclear localization signal by importin beta |
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Authors: | Cingolani Gino Bednenko Janna Gillespie Matthew T Gerace Larry |
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Institution: | Departments of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA. |
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Abstract: | Nuclear import of proteins containing a classical nuclear localization signal (NLS) involves NLS recognition by importin alpha, which associates with importin beta via the IBB domain. Other proteins, including parathyroid hormone-related protein (PTHrP), are imported into the nucleus by direct interaction with importin beta. We solved the crystal structure of a fragment of importin beta-1 (1-485) bound to the nonclassical NLS of PTHrP. The structure reveals a second extended cargo binding site on importin beta distinct from the IBB domain binding site. Using a permeabilized cell import assay we demonstrate that importin beta (1-485) can import PTHrP-coupled cargo in a Ran-dependent manner. We propose that this region contains a prototypical nuclear import receptor domain, which could have evolved into the modern importin beta superfamily. |
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