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PDBsum entry 1m45
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Cell cycle protein
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PDB id
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1m45
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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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Two distinct myosin light chain structures are induced by specific variations within the bound iq motifs-Functional implications.
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Authors
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M.Terrak,
G.Wu,
W.F.Stafford,
R.C.Lu,
R.Dominguez.
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Ref.
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EMBO J, 2003,
22,
362-371.
[DOI no: ]
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PubMed id
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Abstract
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IQ motifs are widespread in nature. Mlc1p is a calmodulin-like myosin light
chain that binds to IQ motifs of a class V myosin, Myo2p, and an IQGAP-related
protein, Iqg1p, playing a role in polarized growth and cytokinesis in
Saccharomyces cerevisiae. The crystal structures of Mlc1p bound to IQ2 and IQ4
of Myo2p differ dramatically. When bound to IQ2, Mlc1p adopts a compact
conformation in which both the N- and C-lobes interact with the IQ motif.
However, in the complex with IQ4, the N-lobe no longer interacts with the IQ
motif, resulting in an extended conformation of Mlc1p. The two light chain
structures relate to two distinct subfamilies of IQ motifs, one of which does
not interact with the N-lobes of calmodulin-like light chains. The correlation
between light chain structure and IQ sequence is demonstrated further by
sedimentation velocity analysis of complexes of Mlc1p with IQ motifs from Myo2p
and Iqg1p. The resulting 'free' N-lobes of myosin light chains in the extended
conformation could mediate the formation of ternary complexes during protein
localization and/or partner recruitment.
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Figure 1.
Figure 1 Ribbon diagram of the structures of Mlc1p bound to IQ2
and IQ4 of Myo2p. (A) Compact structure of the Mlc1p -IQ2
complex. The N-lobe, the C-lobe and the IQ peptide are shown in
blue, red and green, respectively (this color scheme is kept
through all the figures). (B) Extended structure of the Mlc1p
-IQ4 complex. (C) Superimposition of the structures of Mlc1p
-IQ2 and Mlc1p -IQ4 (thinner trace). (D) Superimposition of the
structures of Mlc1p -IQ2 with those of ELC -IQ complexes from
scallop (yellow) and smooth muscle (pink) myosins (Xie et al.,
1994; Houdusse and Cohen, 1996; Dominguez et al., 1998). Note
how differences in the orientation of the N-lobes are mirrored
by differences in the orientation of the C-terminal portions of
the IQ motifs. (E) Superimposition of the extended structures of
Mlc1p -IQ4 and scallop RLC -IQ (cyan) complexes. The myosin
heavy chain fragment (yellow) bound to the scallop RLC is bent
by  90°.
The Mg2+-bound (and fully open) N-lobe of the RLC binds to a
conserved sequence (WQWWKLYSKVKPLL) of the myosin heavy chain
that follows immediately after the 90° turn. Note that this
N-lobe-specific target sequence does not make up part of a
canonical IQ motif.
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Figure 5.
Figure 5 IQ motif-binding interface of Mlc1p. (A) Compact
conformation of the Mlc1p -IQ2 complex. The view is along the
axis of the  -helices
of IQ2 (shown in green). The amino acids of Mlc1p are colored
yellow, except for those amino acids that make direct contacts
with the IQ peptide, which are depicted in red (the same amino
acids are also colored red in Figure 3A). Two views are shown:
on the left side of the figure, the IQ peptide has been moved
out of its binding cleft manually to illustrate better the
binding interface, while the view on the right side corresponds
to the actual position of the IQ peptide in the crystal
structure. (B) Extended structure of Mlc1p -IQ4 (same color
scheme and orientation as A). Note how all of the amino acids of
the N-lobe that interact with IQ2 in the compact structure
become solvent exposed in this complex. The resulting surface
would be available for interactions with a GxxxR-containing
target without a need for the N-lobe to open.
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The above figures are
reprinted
from an Open Access publication published by Macmillan Publishers Ltd:
EMBO J
(2003,
22,
362-371)
copyright 2003.
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Secondary reference #1
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Title
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Crystallization, X-Ray characterization and selenomethionine phasing of mlc1p bound to iq motifs from myosin V.
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Authors
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M.Terrak,
L.R.Otterbein,
G.Wu,
L.A.Palecanda,
R.C.Lu,
R.Dominguez.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2002,
58,
1882-1885.
[DOI no: ]
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PubMed id
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Figure 2.
Figure 2 Representative sections of the DM-refined SeMet MAD
maps of the Mlc1p-IQ4 (a) and Mlc1p-IQ2,3 (b) complexes
calculated at 2.9 Å resolution and displayed at 1.2  .
The maps are superimposed on the partially refined atomic models
of the structures.
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The above figure is
reproduced from the cited reference
with permission from the IUCr
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