Structural basis for nuclear import complex dissociation by RanGTP.
Nuclear protein import is mediated mainly by the transport factor importin-beta that binds cytoplasmic cargo, most often via the importin-alpha adaptor, and then transports it through nuclear pore complexes. This active transport is driven by disassembly of the import complex by nuclear RanGTP. The switch I and II loops of Ran change conformation with nucleotide state, and regulate its interactions with nuclear trafficking components. Importin-beta consists of 19 HEAT repeats that are based on a pair of antiparallel alpha-helices (referred to as the A- and B-helices). The HEAT repeats stack to yield two C-shaped arches, linked together to form a helicoidal molecule that has considerable conformational flexibility. Here we present the structure of full-length yeast importin-beta (Kap95p or karyopherin-beta) complexed with RanGTP, which provides a basis for understanding the crucial cargo-release step of nuclear import. We identify a key interaction site where the RanGTP switch I loop binds to the carboxy-terminal arch of Kap95p. This interaction produces a change in helicoidal pitch that locks Kap95p in a conformation that cannot bind importin-alpha or cargo. We suggest an allosteric mechanism for nuclear import complex disassembly by RanGTP.
Lee
Soo Jae
SJ
MRC Laboratory of Molecular Biology, Hills Rd, Cambridge CB2 2QH, UK.
Matsuura
Yoshiyuki
Y
Liu
Sai Man
SM
Stewart
Murray
M
D021581:Active Transport, Cell Nucleus; D000494:Allosteric Regulation; D001665:Binding Sites; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae; D013329:Structure-Activity Relationship; D028961:beta Karyopherins / Q000737:chemistry* / Q000378:metabolism*; D020931:ran GTP-Binding Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D046912:Multiprotein Complexes; D028961:beta Karyopherins; D020931:ran GTP-Binding Protein