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PDBsum entry 2q5d
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Protein transport
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PDB id
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2q5d
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References listed in PDB file
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Key reference
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Title
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Molecular basis for the recognition of snurportin 1 by importin beta.
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Authors
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G.Mitrousis,
A.S.Olia,
N.Walker-Kopp,
G.Cingolani.
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Ref.
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J Biol Chem, 2008,
283,
7877-7884.
[DOI no: ]
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PubMed id
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Abstract
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The nuclear import of uridine-rich ribonucleoproteins is mediated by the
transport adaptor snurportin 1 (SNP1). Similar to importin alpha, SNP1 uses an
N-terminal importin beta binding (sIBB) domain to recruit the receptor importin
beta and gain access to the nucleus. In this study, we demonstrate that the sIBB
domain has a bipartite nature, which contains two distinct binding determinants
for importin beta. The first determinant spans residues 25-65 and includes the
previously identified importin alpha IBB (alphaIBB) region of homology. The
second binding determinant encompasses residues 1-24 and resembles region
1011-1035 of the nucleoporin 153 (Nup153). The two binding determinants
synergize within the sIBB domain to confer a low nanomolar binding affinity for
importin beta (K(d) approximately 2 nm) in an interaction that, in vitro, is
displaced by RanGTP. We propose that in vivo the synergy of Nup153 and nuclear
RanGTP promotes translocation of uridine-rich ribonucleoproteins into the
nucleus.
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Figure 2.
FIGURE 2. Structural plasticity of importin β bound to the
sIBB-(25-65) domain. a, ribbon diagram of the asymmetric unit
content of crystal form II, determined at 3.2 Å
resolution. The two complexes in the asymmetric unit have
different conformations. In complex B, on the left (in cyan),
importin β adopts an open conformation, and only the
sIBB-(40-65) helix is visible (in yellow). In complex A, on the
right (in green), importin β has a conformation identical to
crystal form I, and all residues for the sIBB-(25-65) domain are
visible (in magenta). b, superimposition of the importin β
structures from complex A (closed) and B (open) reveals
deviations up to 20 Å in the C terminus of the protein.
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Figure 3.
FIGURE 3. sIBB-(25-65) domain versus  IBB-(11-54) domain. a,
left panel, structure of importin β- IBB complex (in purple
and blue, respectively) superimposed to that of the importin
β-sIBB-(25-65) complex (in green and magenta, respectively) of
crystal form I. Right panel, blowup of the IBB and sIBB-(25-65)
domains (colored in blue and magenta, respectively) translated
out of the superimposition. Significant differences are observed
in the structure of the two peptides. b, schematic diagram of
the interactions between HEAT repeats 7-19 of importin β and
the sIBB-(25-65) domain (top) as compared with the IBB-(11-54) domain
(bottom). HEAT repeats are referred to as H7-19. Colored in red
in the primary sequence of the sIBB-(25-65) and IBB-(11-54) domain are
identical residues. Intermolecular polar and hydrophobic
interactions are shown as red and green lines, respectively.
Intramolecular contacts within IBB domains are indicated by red
brackets.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2008,
283,
7877-7884)
copyright 2008.
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