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PDBsum entry 1top
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Contractile system protein
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PDB id
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1top
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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 chicken skeletal muscle troponin c at 1.78 a resolution.
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Authors
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K.A.Satyshur,
D.Pyzalska,
M.Greaser,
S.T.Rao,
M.Sundaralingam.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 1994,
50,
40-49.
[DOI no: ]
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PubMed id
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Note In the PDB file this reference is
annotated as "TO BE PUBLISHED".
The citation details given above were identified by an automated
search of PubMed on title and author
names, giving a
percentage match of
76%.
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Abstract
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The structure of chicken skeletal muscle troponin C (TnC) has been refined to an
R value of 0.168, using 14 788 reflections, in the resolution range 8.0-1.78 A.
Our earlier 2 A resolution structure [Satyshur, Rao, Pyzalska, Drendel, Greaser
& Sundaralingam (1988). J. Biol. Chem. 263, 1628-1647] served as the
starting model. The refined model includes atoms for all protein residues
(1-162), 2 Ca(2+) ions, 169 water molecules and one sulfate ion. The
high-resolution refinement shows more clearly the details of the protein and
water structure. The side chains Glu63, Cysl01, Arg123, Aspl40 and Asp152 adopt
two discretely ordered conformations. The long central helix is only slightly
curved/bent (7.9 degrees ) and all the central helix NH.O=C hydrogen bonds are
intact. Seven of the nine carbonyl O atoms of the mid segment of this helix,
including the D/E linker region, are hydrogen bonded to water molecules which
weakens the helix hydrogen bonds. In contrast, in each of the protected upper
and lower thirds of the long central helix, only two carbonyl O atoms are
hydrogen bonded to water molecules. The hydrogen-bonding patterns displayed by
some of the carbonyl O atoms of NT and A helices of the N-terminal domain and
the F and H helices of the C-terminal domain, which are on the exposed surface
of the protein, are similar. The B helix of the calcium-free site I is kinked,
with the local helix axes at either end making an angle of 39 degrees, by two
inserted water molecules between N-H and O=C groups, breaking the adjacent helix
hydrogen bonds. A sulfate ion from the crystallization buffer is also trapped in
the B helix between the guanidinium group of Arg47 and these two inserted water
molecules. The C helix of site II is devoid of similar hydration and is probably
responsible for the different interhelical angles A/B at site I (134 degrees )
and C/D at site II (149 degrees ). Extensive interhelix hydrogen bonds occur
between the side chains of the C and D helices of the 'apo' site II:
Gln51-Asp89, Asn52-Asp89, Glu57-Gln85, Glu57-Glu88 and Glu64-Arg84, which
apparently are disrupted upon Ca uptake and the resulting rearrangement of the
helices expose the side chains, lining the palm of the N-(and C-) terminal
domains, for interaction with specific peptide fragment of troponin I (Tnl)
during muscle contraction. The dominant crystal packing motif involves a
head-to-tail interaction between the N-terminal domain A helix of one molecule
and the palm of the C-terminal domain of the 3(2)-related molecule, in a manner
similar to that which can be expected for the TnC-TnI complex. Similar
interactions may also be responsible for the dimerization of TnC at low pH.
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Figure 7.
Fig. 7. Stereoviews of the Edmondson wheels of the long central
helix. (a) The Nterminal residues 7683 with three waters, (b)
middle of th helix, residues 8496, with eight waters and (c)
Cterminal residues 97105 with one water. Notice that the
hydrophobic residues line pposite faces of the long helix at the
two ends (a) and (c).
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Figure 10.
Fig. 10. Steeo diagram of the intermolecular inteaction between
Cysl01, with its side chain discretely ordered over two sites (one
shown as solid bond and the other as broken), and residues
2428 of the A helix of the molecule related by a 32 axis (open
bonds). The water molecule 281 interacts with both S r sites of
Cysl01 (2.50, 3.05/~,), the carbonyl O atom of Ala24 (3.35 A)
and water 363 (2.64 A). One site of S r (broken bond) forms a
hydrogen bond with SD of Met28 (2.97 ~,).
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The above figures are
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(1994,
50,
40-49)
copyright 1994.
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Secondary reference #1
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Title
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Refined structure of chicken skeletal muscle troponin c in the two-Calcium state at 2-A resolution.
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Authors
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K.A.Satyshur,
S.T.Rao,
D.Pyzalska,
W.Drendel,
M.Greaser,
M.Sundaralingam.
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Ref.
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J Biol Chem, 1988,
263,
1628-1647.
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PubMed id
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Secondary reference #2
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Title
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Molecular structure of troponin c from chicken skeletal muscle at 3-Angstrom resolution.
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Authors
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M.Sundaralingam,
R.Bergstrom,
G.Strasburg,
S.T.Rao,
P.Roychowdhury,
M.Greaser,
B.C.Wang.
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Ref.
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Science, 1985,
227,
945-948.
[DOI no: ]
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PubMed id
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Secondary reference #3
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Title
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X-Ray diffraction studies of troponin-C crystals from rabbit and chicken skeletal muscles.
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Authors
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G.M.Strasburg,
M.L.Greaser,
M.Sundaralingam.
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Ref.
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J Biol Chem, 1980,
255,
3806-3808.
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PubMed id
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Secondary reference #4
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Title
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The amino acid sequence of troponin c from chicken skeletal muscle.
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Author
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J.M.Wilkinson.
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Ref.
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Febs Lett, 1976,
70,
254-256.
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PubMed id
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