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PDBsum entry 2d1k
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Structural protein
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PDB id
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2d1k
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Contents |
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371 a.a.
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260 a.a.
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29 a.a.
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References listed in PDB file
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Key reference
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Title
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Structural basis for the actin-Binding function of missing-In-Metastasis.
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Authors
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S.H.Lee,
F.Kerff,
D.Chereau,
F.Ferron,
A.Klug,
R.Dominguez.
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Ref.
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Structure, 2007,
15,
145-155.
[DOI no: ]
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PubMed id
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Abstract
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The adaptor protein missing-in-metastasis (MIM) contains independent F- and
G-actin binding domains, consisting, respectively, of an N-terminal 250 aa
IRSp53/MIM homology domain (IMD) and a C-terminal WASP-homology domain 2 (WH2).
We determined the crystal structures of MIM's IMD and that of its WH2 bound to
actin. The IMD forms a dimer, with each subunit folded as an antiparallel
three-helix bundle. This fold is related to that of the BAR domain. Like the BAR
domain, the IMD has been implicated in membrane binding. Yet, comparison of the
structures reveals that the membrane binding surfaces of the two domains have
opposite curvatures, which may determine the type of curvature of the
interacting membrane. The WH2 of MIM is longer than the prototypical WH2,
interacting with all four subdomains of actin. We characterize a similar WH2 at
the C terminus of IRSp53 and propose that in these two proteins WH2 performs a
scaffolding function.
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Figure 3.
Figure 3. Structural and Functional Relationship between the
IMD and BAR Domains
(A) Electrostatic surface
representation of the IMD dimer calculated with the program APBS
(Baker et al., 2001) and displayed with the program PyMOL
(http://www.pymol.org). Red and blue indicate negatively and
positively charged regions, respectively (red, −6 kTe^−1;
blue +6 kTe^−1). Note the positively charged and slightly
convex surface, which is thought to mediate the interactions
with membranes of the IMD (Suetsugu et al., 2006).
(B)
Similar electrostatic representation of the BAR domain of
amphiphysin (Peter et al., 2004). The orientation is the same as
in (A). Note that the shape of the positively charged membrane
binding surface of the BAR domain is concave.
(C)
Superimposition of the structures of the IMD of MIM (blue,
yellow) with that of the BAR domain of arfaptin complexed with
Rac (Tarricone et al., 2001) (gray). The orientation is the same
as in (A) and (B). The two folds have different curvatures, but
superimpose well in the middle section where the dimers overlap,
suggesting that this region may also mediate the binding of Rac
in MIM and IRSp53.
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Figure 4.
Figure 4. The WASP-Homology Domain 2 of MIM and IRSp53
(A) Comparison of a classical WH2 (represented by WASP,
Wiskott-Aldrich syndrome protein) with the WH2s of MIM, ABBA,
and IRSp53. Red, blue, green, and yellow correspond to
negatively charged, positively charged, hydrophobic, and small
(Thr, Val, Ser, Ala) conserved amino acids, respectively. The
diagram above the sequences represents a secondary structure
assignment based on the structure determined here (cylinder, α
helix; arrow, β strand). Accession numbers are as in Figure 1,
and WASP_HUMAN, P42768. Red arrows point to noncanonical amino
acids present in the WH2 of IRSp53.
(B) Structure of the
WH2 of MIM (red ribbon) bound to actin (gray surface). Numbers
1–4 indicate actin's four subdomains. The side chains of some
of the amino acids involved in interactions with actin are shown
(green, hydrophobic; blue, positively charged).
(C) Binding
of the WH2 of IRSp53 to actin measured by ITC. The upper graph
corresponds to the heat evolved upon repeated 10 μl injections
of a 100 μM solution of the WH2 peptide into a 10 μM solution
of actin in G buffer. The lower graph shows the binding isotherm
produced by integration of the heat for each injection. The line
represents a nonlinear least squares fit to the data using a
single-site binding model. The following thermodynamic
parameters were determined from the fitting: dissociation
constant K[d] = 0.28 ± 0.04 μM; molar enthalpy ΔH =
−7.2 ± 0.1 kcal.mol^−1; and stoichiometry n = 0.9.
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The above figures are
reprinted
from an Open Access publication published by Cell Press:
Structure
(2007,
15,
145-155)
copyright 2007.
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