Importin

spinqualitylabelsall models Structure of yeast importinα NLS-binding domain (grey) complex with nucleoplasmin peptide (green) (PDB code 1ee5). Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Function Importins (IPO) mediate the import of cellular proteins into the nucleus by binding to the Nuclear Localization Signal (NLS). IPO has 2 subunits: α and β. IPO-α is an adaptor protein which binds the NLS. IPOs can contain one or two NLS motifs. IPO-α contains several armadillo repeats with two NLS-binding sites and an IPO-β binding (IBB) site. IPO-β contains 19 HEAT (solenoid domain) repeats. Many nuclear proteins contain Phe-Gly sequences which can bind to HEAT repeats and thus be transported. IPO-4 binds histones H3 and H4 and histone chaperone ASF1 for nuclear import. IPO-7 drives the nuclear import of the regulator of mechanotransduction pathway YAP. IPO-9 binds histones H2A and H2B for nuclear import. IPO-13 has a role in oxidative stress-dependent nuclear export. See also Protein Transport Membrane Protein. Disease IPO-α isoform expression is altered in many kinds of cancer. Relevance Specific IPO-α isoforms are critical in nerve regenerative response after injury. Loss of IPO-α expression in aging myocardial cells could make recovery after heart disease in elderly patients more difficult. 3D structures of importin Importin 3D structures

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Michal Harel, Joel L. Sussman