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PDBsum entry 2iep
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Signaling protein,transferase
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PDB id
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2iep
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References listed in PDB file
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Key reference
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Title
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Crystal structure of the agrin-Responsive immunoglobulin-Like domains 1 and 2 of the receptor tyrosine kinase musk.
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Authors
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A.L.Stiegler,
S.J.Burden,
S.R.Hubbard.
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Ref.
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J Mol Biol, 2006,
364,
424-433.
[DOI no: ]
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PubMed id
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Abstract
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Muscle-specific kinase (MuSK) is a receptor tyrosine kinase expressed
exclusively in skeletal muscle, where it is required for formation of the
neuromuscular junction. MuSK is activated by agrin, a neuron-derived heparan
sulfate proteoglycan. Here, we report the crystal structure of the
agrin-responsive first and second immunoglobulin-like domains (Ig1 and Ig2) of
the MuSK ectodomain at 2.2 A resolution. The structure reveals that MuSK Ig1 and
Ig2 are Ig-like domains of the I-set subfamily, which are configured in a
linear, semi-rigid arrangement. In addition to the canonical internal disulfide
bridge, Ig1 contains a second, solvent-exposed disulfide bridge, which our
biochemical data indicate is critical for proper folding of Ig1 and processing
of MuSK. Two Ig1-2 molecules form a non-crystallographic dimer that is mediated
by a unique hydrophobic patch on the surface of Ig1. Biochemical analyses of
MuSK mutants introduced into MuSK(-/-) myotubes demonstrate that residues in
this hydrophobic patch are critical for agrin-induced MuSK activation.
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Figure 2.
Figure 2. MuSK Ig1-2 dimer. (a) Ribbon diagram of the MuSK
Ig1-2 non-crystallographic dimer. The two protomers are colored
green and purple (Ig1 in light shades and Ig2 in dark shades).
The non-crystallographic 2-fold axis is vertical. (b) Ig1–Ig1
dimer interface. The stereo view is approximately 50° about
the vertical (2-fold) axis from that in (a). Side-chain atoms in
the dimer interface are shown in ball-and-stick representation,
and hydrophobic contacts are shown with semi-transparent van der
Waals surfaces. Carbon atoms, either green or purple; oxygen
atoms, red; and sulfur atoms, yellow. Side-chains that are not
labeled are related by the vertical 2-fold axis to those that
are labeled. (c) Molecular surface representation of Ig1-2
colored according to electrostatic potential: blue, positive (+
15kT); white, neutral; red, negative (− 15kT). Residues
located in the Ig1 dimer interface (left) and in the vicinity of
the surface-exposed disulfide bridge (Cys98/Cys112) (right), on
the opposite side of Ig1, are labeled. The two views are related
by 180° about a vertical axis. (a) and (b) were rendered
with PyMOL [http://pymol.sourceforge.net] and (c) with GRASP.^45
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Figure 4.
Figure 4. Mutations in MuSK Ig1 affect agrin-induced
receptor activation. (a) Ile96 and (b) Met48 and Leu83 are
required for agrin-induced activation. MuSK^−/− myotubes
stably expressing MuSK-GFP (wild-type or mutant) were stimulated
with 0.1 nM or 0.5 nM neural agrin for 30 min followed by MuSK
immunoprecipitation (IP) with the C-terminal anti-MuSK antibody.
IP samples were resolved by SDS-PAGE and immunoblotted (IB) with
an anti-phosphotyrosine antibody (anti-pTyr) to assess MuSK
activation. Blotting a duplicate membrane with anti-GFP antibody
shows the relative level of MuSK-GFP in each sample.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2006,
364,
424-433)
copyright 2006.
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