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PDBsum entry 1j1e
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Contractile protein
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PDB id
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1j1e
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Contents |
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158 a.a.
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69 a.a.
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118 a.a.
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159 a.a.
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75 a.a.
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141 a.a.
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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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Structure of the core domain of human cardiac troponin in the ca(2+)-Saturated form.
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Authors
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S.Takeda,
A.Yamashita,
K.Maeda,
Y.Maéda.
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Ref.
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Nature, 2003,
424,
35-41.
[DOI no: ]
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PubMed id
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Abstract
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Troponin is essential in Ca(2+) regulation of skeletal and cardiac muscle
contraction. It consists of three subunits (TnT, TnC and TnI) and, together with
tropomyosin, is located on the actin filament. Here we present crystal
structures of the core domains (relative molecular mass of 46,000 and 52,000) of
human cardiac troponin in the Ca(2+)-saturated form. Analysis of the
four-molecule structures reveals that the core domain is further divided into
structurally distinct subdomains that are connected by flexible linkers, making
the entire molecule highly flexible. The alpha-helical coiled-coil formed
between TnT and TnI is integrated in a rigid and asymmetric structure (about 80
angstrom long), the IT arm, which bridges putative tropomyosin-anchoring
regions. The structures of the troponin ternary complex imply that Ca(2+)
binding to the regulatory site of TnC removes the carboxy-terminal portion of
TnI from actin, thereby altering the mobility and/or flexibility of troponin and
tropomyosin on the actin filament.
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Figure 4.
Figure 4: Side-chain interactions between the subunits. a, A
stereo view of the interactions between the three chains around
the C lobe of TnC. b, The hydrophobic residues in the N lobe of
TnC interacting with segment H3(I) of TnI. TnC, TnI and TnT are
coloured pink, cyan and yellow, respectively. The amino acid
residues involved in the interactions are shown in ball and
stick representation. The three Ca^2+ ions bound to sites II,
III and IV are shown by the black spheres.
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Figure 5.
Figure 5: A schematic representation of the interactions between
troponin and other thin filament components. The potential
actin-tropomyosin-binding portions, which are not included in
the current structural model, are schematically drawn: TnT1 and
C-TnT are yellow ellipsoids, and the inhibitory region (IR) and
the C terminus of TnI (C-TnI) are blue ellipsoids. The actin and
the tropomyosin strands are in green and brown, respectively.
The black arrows indicate the interactions between troponin and
tropomyosin-actin.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2003,
424,
35-41)
copyright 2003.
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Secondary reference #1
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Title
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Structural and functional domains of the troponin complex revealed by limited digestion.
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Authors
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S.Takeda,
T.Kobayashi,
H.Taniguchi,
H.Hayashi,
Y.Maéda.
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Ref.
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Eur J Biochem, 1997,
246,
611-617.
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PubMed id
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Secondary reference #2
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Title
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Crystal structure of troponin c in complex with troponin i fragment at 2.3-A resolution.
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Authors
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D.G.Vassylyev,
S.Takeda,
S.Wakatsuki,
K.Maeda,
Y.Maéda.
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Ref.
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Proc Natl Acad Sci U S A, 1998,
95,
4847-4852.
[DOI no: ]
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PubMed id
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Figure 1.
Fig. 1. Structure of the TnC/TnI[1-47] complex. (A)
Ribbon diagram of the TnC/TnI[1-47] complex structure. The  -helices,
 -strands,
and loops of TnC are in red, green, and yellow, respectively.
The unwound and kinked central D/E -helix of
TnC is shown in blue, and the interdomain extended linker is
black. The two calcium ions in the TnC C-lobe are shown as black
balls. The TnI[1-47] -helix is
in cyan. The figure was drawn with the MOLSCRIPT program (21).
(B) Hydrophobic (green arrows) and polar (red arrows) side-chain
interactions between TnI[1-47] (circles) and TnC (rectangles)
residues in the TnC/TnI[1-47] complex. The hydrophobic and polar
residues are shown in green and red, respectively. Water
molecules are shown as cyan hexagons. Main chain carbonyl
oxygens of the interacting amino acids are shown as a red O
attached to the subsequent residues. (C) Portion of the final
(2Fo-Fc) electron density map and the TnC/TnI[1-47] model (ball
and stick) in the hydrophobic cavity of the C-lobe of TnC. The
TnI and TnC residues are shown in cyan and atom-dependent (C, N,
O, and S are yellow, blue, red, and green, respectively) colors,
respectively. Met-21, protruding into hydrophobic cleft of TnC,
is colored red. The figure was produced with the O program (19).
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Figure 3.
Fig. 3. TnC/TnI[reg] model structure. The figure was
prepared by using MOLSCRIPT (21). (A) Ribbon diagram of the
TnC/TnI[1-47]/TnI[reg] model. The two "open" N- and C-lobes of
TnC are green and red, respectively. Four calcium ions are shown
as black balls. The TnI[1-47] and TnI[reg] -helices
are shown in cyan and yellow, respectively. The two-proline
linker (Pro-109 and Pro-110) in the TnI[reg] -helix is
shown in blue. (B) Stereo view of the hydrophobic core of the
TnC/TnI[reg] model structure. The TnC and TnI[reg] -helices
are shown in blue and yellow, respectively. The side chains of
the residues in the hydrophobic pocket of the "open" C-lobe of
TnC and the complementary hydrophobic residues of TnI[reg] (ball
and stick) are cyan and green, respectively. Protruding side
chain of Met-121 is shown in red.
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