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Moeller, Holger von (2009): Structural and Biochemical Studies of the Human DEAD-box Helicase Dbp5 and Nucleoporin Nup214 Involved in mRNA Export. Dissertation, LMU München: Faculty of Chemistry and Pharmacy
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Abstract

The hallmark of eukaryotic evolution was the development of the nucleus in cells. This compartmentalization requires the nucleocytoplasmic transport of thousands of molecules. The gate into and out of the nucleus is the nuclear pore complex (NPC). One of the molecules that needs to be exported from the nucleus is messenger RNA (mRNA). mRNA associates with proteins in the nucleus forming a messenger ribonucleoprotein particle (mRNP). mRNPs bind to dedicated transport factors that facilitate movement through the NPC. One protein that associates to mRNPs is the helicase Dbp5, which belongs to the DEAD-box family of RNA helicases. Dbp5 is essential for mRNA export in both yeast and humans. It binds RNA and is concentrated and locally activated at the cytoplasmic side of the nuclear pore complex, where it interacts with the cytoplasmic nucleoporin Nup214. In my PhD work, I have determined the crystal structures of human Dbp5 bound to RNA and AMPPNP, and bound to Nup214. I designed and performed in vitro assays, which show that binding of Dbp5 to nucleic acid and to Nup214 is mutually exclusive. The interactions are mediated by conserved residues, implying a conserved recognition mechanism. These results suggest a framework for the consecutive steps leading to the release of mRNA at the final stages of nuclear export. More generally, they provide a paradigm for how binding of regulators can specifically inhibit DEAD-box proteins.