title: An allosteric mechanism to displace nuclear export cargo from CRM1 and RanGTP by RanBP1.
abstract: The karyopherin CRM1 mediates nuclear export of proteins and ribonucleoproteins bearing a leucine-rich nuclear export signal (NES). To elucidate the precise mechanism by which NES-cargos are dissociated from CRM1 in the cytoplasm, which is important for transport directionality, we determined a 2.0-A resolution crystal structure of yeast CRM1:RanBP1:RanGTP complex, an intermediate in the disassembly of the CRM1 nuclear export complex. The structure shows that on association of Ran-binding domain (RanBD) of RanBP1 with CRM1:NES-cargo:RanGTP complex, RanBD and the C-terminal acidic tail of Ran induce a large movement of the intra-HEAT9 loop of CRM1. The loop moves to the CRM1 inner surface immediately behind the NES-binding site and causes conformational rearrangements in HEAT repeats 11 and 12 so that the hydrophobic NES-binding cleft on the CRM1 outer surface closes, squeezing out the NES-cargo. This allosteric mechanism accelerates dissociation of NES by over two orders of magnitude. Structure-based mutagenesis indicated that the HEAT9 loop also functions as an allosteric autoinhibitor to stabilize CRM1 in a conformation that is unable to bind NES-cargo in the absence of RanGTP.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Koyama
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Matsuura
mesh_terms: D021581:Active Transport, Cell Nucleus; D000494:Allosteric Regulation; D018360:Crystallography, X-Ray; D006160:Guanosine Triphosphate / Q000737:chemistry* / Q000378:metabolism*; D028884:Karyopherins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000502:physiology; D000097606:Exportin 1 Protein
chemical_list: D006160:Guanosine Triphosphate; D028884:Karyopherins; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D000097606:Exportin 1 Protein; C091775:ran-binding protein 1