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PDBsum entry 1jc2
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Structural protein
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PDB id
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1jc2
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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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Structure, Dynamics, And thermodynamics of the structural domain of troponin c in complex with the regulatory peptide 1-40 of troponin i.
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Authors
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P.Mercier,
L.Spyracopoulos,
B.D.Sykes.
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Ref.
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Biochemistry, 2001,
40,
10063-10077.
[DOI no: ]
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PubMed id
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Abstract
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The structure of the calcium-saturated C-domain of skeletal troponin C (CTnC) in
complex with a regulatory peptide comprising residues 1-40 (Rp40) of troponin I
(TnI) was determined using nuclear magnetic resonance (NMR) spectroscopy. The
solution structure determined by NMR is similar to the structure of the C-domain
from intact TnC in complex with TnI(1)(-)(47) determined by X-ray
crystallography [Vassylyev, D. G., Takeda, S., Wakatsuki, S., Maeda, K., and
Maeda, Y. (1998) Proc. Natl. Acad. Sci. U.S.A. 95, 4847-4852]. Changes in the
dynamic properties of CTnC.2Ca2+ induced by Rp40 binding were investigated using
backbone amide (15)N NMR relaxation measurements. Analysis of NMR relaxation
data allows for extraction of motional order parameters on a per residue basis,
from which the contribution of changes in picosecond to nanosecond time scale
motions to the conformational entropy associated with complex formation can be
estimated. The results indicate that binding of Rp40 decreases backbone
flexibility in CTnC, particularly at the end of the C-terminal helix. The
backbone conformational entropy change (-TDeltaS) associated with binding of
Rp40 to CTnC.2Ca2+ determined from (15)N relaxation data is 9.6 +/- 0.7 kcal
mol(-1) at 30 degrees C. However, estimation of thermodynamic quantities using a
structural approach [Lavigne, P., Bagu, J. R., Boyko, R., Willard, L., Holmes,
C. F., and Sykes, B. D. (2000) Protein Sci. 9, 252-264] reveals that the change
in solvation entropy upon complex formation is dominant and overcomes the
thermodynamic "cost" associated with "stiffening" of the protein backbone upon
Rp40 binding. Additionally, backbone amide (15)N relaxation data measured at
different concentrations of CTnC.2Ca2+.Rp40 reveal that the complex dimerizes in
solution. Fitting of the apparent global rotational correlation time as a
function of concentration to a monomer-dimer equilibrium yields a dimerization
constant of approximately 8.3 mM.
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