title: MD simulations and FRET reveal an environment-sensitive conformational plasticity of importin-β.
abstract: The nuclear pore complex mediates nucleocytoplasmic transport of macromolecules in eukaryotic cells. Transport through the pore is restricted by a hydrophobic selectivity filter comprising disordered phenylalanine-glycine-rich repeats of nuclear pore proteins. Exchange through the pore requires specialized transport receptors, called exportins and importins, that interact with cargo proteins in a RanGTP-dependent manner. These receptors are highly flexible superhelical structures composed of HEAT-repeat motifs that adopt various degrees of extension in crystal structures. Here, we performed molecular-dynamics simulations using crystal structures of Importin-β in its free form or in complex with nuclear localization signal peptides as the starting conformation. Our simulations predicted that initially compact structures would adopt extended conformations in hydrophilic buffers, while contracted conformations would dominate in more hydrophobic solutions, mimicking the environment of the nuclear pore. We confirmed this experimentally by Förster resonance energy transfer experiments using dual-fluorophore-labeled Importin-β. These observations explain seemingly contradictory crystal structures and suggest a possible mechanism for cargo protection during passage of the nuclear pore. Such hydrophobic switching may be a general principle for environmental control of protein function.
authors.affiliation: Free Floater (Junior) Research Group "Applied Synthetic Biology", Institute for Microbiology and Genetics, Georg-August University Göttingen, Göttingen, Germany.
authors.forename: Kangkan
authors.initials: K
authors.lastname: Halder
authors.affiliation: Department of Theoretical and Computational Biophysics, Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Dölker
authors.affiliation: Third Institute of Physics-Biophysics, Georg-August University Göttingen, Göttingen, Germany.
authors.forename: Qui
authors.initials: Q
authors.lastname: Van
authors.affiliation: Third Institute of Physics-Biophysics, Georg-August University Göttingen, Göttingen, Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Gregor
authors.affiliation: Institute for Microbiology and Genetics, Department of Molecular Structural Biology, Georg-August University Göttingen, Göttingen, Germany.
authors.forename: Achim
authors.initials: A
authors.lastname: Dickmanns
authors.affiliation: Department of Molecular Biology, Faculty of Medicine, Georg-August University Göttingen, Göttingen, Germany.
authors.forename: Imke
authors.initials: I
authors.lastname: Baade
authors.affiliation: Department of Molecular Biology, Faculty of Medicine, Georg-August University Göttingen, Göttingen, Germany.
authors.forename: Ralph H
authors.initials: RH
authors.lastname: Kehlenbach
authors.affiliation: Institute for Microbiology and Genetics, Department of Molecular Structural Biology, Georg-August University Göttingen, Göttingen, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Ficner
authors.affiliation: Third Institute of Physics-Biophysics, Georg-August University Göttingen, Göttingen, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Enderlein
authors.affiliation: Department of Theoretical and Computational Biophysics, Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany. Electronic address: hgrubmu@gwdg.de.
authors.forename: Helmut
authors.initials: H
authors.lastname: Grubmüller
authors.affiliation: Free Floater (Junior) Research Group "Applied Synthetic Biology", Institute for Microbiology and Genetics, Georg-August University Göttingen, Göttingen, Germany. Electronic address: hneumann@uni-goettingen.de.
authors.forename: Heinz
authors.initials: H
authors.lastname: Neumann
mesh_terms: D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D018583:Pliability; D011487:Protein Conformation; D012996:Solutions; D012997:Solvents / Q000737:chemistry; D014867:Water / Q000737:chemistry; D028961:beta Karyopherins / Q000737:chemistry*
chemical_list: D012996:Solutions; D012997:Solvents; D028961:beta Karyopherins; D014867:Water