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PDBsum entry 1gcj
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Transport protein
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PDB id
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1gcj
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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The adoption of a twisted structure of importin-Beta is essential for the protein-Protein interaction required for nuclear transport.
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Authors
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S.J.Lee,
N.Imamoto,
H.Sakai,
A.Nakagawa,
S.Kose,
M.Koike,
M.Yamamoto,
T.Kumasaka,
Y.Yoneda,
T.Tsukihara.
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Ref.
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J Mol Biol, 2000,
302,
251-264.
[DOI no: ]
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PubMed id
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Abstract
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Importin-beta is a nuclear transport factor which mediates the nuclear import of
various nuclear proteins. The N-terminal 1-449 residue fragment of mouse
importin-beta (impbeta449) possesses the ability to bidirectionally translocate
through the nuclear pore complex (NPC), and to bind RanGTP. The structure of the
uncomplexed form of impbeta449 has been solved at a 2.6 A resolution by X-ray
crystallography. It consists of ten copies of the tandemly arrayed HEAT repeat
and exhibits conformational flexibility which is involved in protein-protein
interaction for nuclear transport. The overall conformation of the HEAT repeats
shows that a twisted motion produces a significantly varied superhelical
architecture from the previously reported structure of RanGTP-bound
importin-beta. These conformational changes appear to be the sum of small
conformational changes throughout the polypeptide. Such a flexibility, which
resides in the stacked HEAT repeats, is essential for interaction with RanGTP or
with NPCs. Furthermore, it was found that impbeta449 has a structural similarity
with another nuclear migrating protein, namely beta-catenin, which is composed
of another type of helix-repeated structure of ARM repeat. Interestingly, the
essential regions for NPC translocation for both importin-beta and beta-catenin
are spatially well overlapped with one another. This strongly indicates the
importance of helix stacking of the HEAT or ARM repeats for NPC-passage.
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Figure 1.
Figure 1. Structure of impb449. (a) Stereo view of impb449
dimer in the asymmetric unit. The crystal structure of the
impb449 molecules forms a dimer, which is composed of molecule
I(pink) and II(green) in the asymmetric unit. Three interaction
sites for dimer formation are depicted by the ball-and-stick
model. The C-terminal area interaction is in purple, and the
second and third interaction sites are in blue and red,
respectively. (b) HEAT repeat helices in impb449. The convex
side of helices of A1-A10 and the concave side of the helices of
B1-B10 and 3[10] helices are colored in blue, red and light
blue, respectively. C2 helix is colored in green. (c) Structural
alignment of the ten HEAT repeats of impb449. The first amino
acid residue of each repeat is indicated on the left. Each
repeat contains helix A and B. The repeat 2 contains helix C.
Underlined residues in repeats 3, 4, and 5 comprise 3[10]
helices indicated in (b).
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Figure 4.
Figure 4. Hypothetically constructed superhelix structures
of three importin-bs. HEAT repeat helices from A3 to B9, stacked
side-by-side, are superposed. The residues of amino acid
residues 1-449 are used for the construction of the superhelix.
One pitch of superhelix is comprised of 24 molecules (impb449),
23 molecules (impb/IBB) and 23 molecules (impb/Ran),
respectively. Left, superhelix of impb449 (monomerI:uncomplexed
form); middle, superhelix of impb/IBB (PDB code 1QGK:RanGTP
uncomplexed form, but complexed with IBB in the C terminal half
of full length of importin-b); right, superhelix of impb/Ran
(PDB code 1IBR, chain B:RanGTP complexed form).
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2000,
302,
251-264)
copyright 2000.
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