Architecture of CRM1/Exportin1 suggests how cooperativity is achieved during formation of a nuclear export complex.
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.
Petosa
Carlo
C
European Molecular Biology Laboratory, Grenoble Outstation, B.P. 181, 38042 Grenoble Cedex 9, France.
Schoehn
Guy
G
Askjaer
Peter
P
Bauer
Ulrike
U
Moulin
Martine
M
Steuerwald
Ulrich
U
Soler-López
Montserrat
M
Baudin
Florence
F
Mattaj
Iain W
IW
Müller
Christoph W
CW
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004305:Dose-Response Relationship, Drug; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted; D028884:Karyopherins / Q000737:chemistry* / Q000378:metabolism; D007930:Leucine / Q000737:chemistry; D008854:Microscopy, Electron; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D028961:beta Karyopherins / Q000737:chemistry; D020931:ran GTP-Binding Protein / Q000378:metabolism; D000097606:Exportin 1 Protein
D005231:Fatty Acids, Unsaturated; D020558:GTP Phosphohydrolases; D006160:Guanosine Triphosphate; D028884:Karyopherins; D007930:Leucine; D018160:Receptors, Cytoplasmic and Nuclear; D028961:beta Karyopherins; D020931:ran GTP-Binding Protein; D000097606:Exportin 1 Protein; C108121:TNPO1 protein, human; C038753:leptomycin B