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  • Title: Architecture of CRM1/Exportin1 suggests how cooperativity is achieved during formation of a nuclear export complex.
    Author: Petosa C, Schoehn G, Askjaer P, Bauer U, Moulin M, Steuerwald U, Soler-López M, Baudin F, Mattaj IW, Müller CW.
    Journal: Mol Cell; 2004 Dec 03; 16(5):761-75. PubMed ID: 15574331.
    Abstract:
    CRM1/Exportin1 mediates the nuclear export of proteins bearing a leucine-rich nuclear export signal (NES) by forming a cooperative ternary complex with the NES-bearing substrate and the small GTPase Ran. We present a structural model of human CRM1 based on a combination of X-ray crystallography, homology modeling, and electron microscopy. The architecture of CRM1 resembles that of the import receptor transportin1, with 19 HEAT repeats and a large loop implicated in Ran binding. Residues critical for NES recognition are identified adjacent to the cysteine residue targeted by leptomycin B (LMB), a specific CRM1 inhibitor. We present evidence that a conformational change of the Ran binding loop accounts for the cooperativity of Ran- and substrate binding and for the selective enhancement of CRM1-mediated export by the cofactor RanBP3. Our findings indicate that a single architectural and mechanistic framework can explain the divergent effects of RanGTP on substrate binding by many import and export receptors.
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