Mimicry of the Calcium-Induced Conformational State of Troponin C by Low Temperature under Pressure

Mimicry of the Calcium-Induced Conformational State of Troponin C by Low Temperature under Pressure

Calcium binding to the N-domain of troponin C initiates a series of conformational changes that lead to muscle contraction. Calcium binding provides the free energy for a hydrophobic region in the core of N-domain to assume a more open configuration. Fluorescence measurements on a tryptophan mutant...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS Vol. 93; no. 20; pp. 10642 - 10646
Main Authors: Foguel, Debora, Suarez, Marisa C., Barbosa, Cristiane, Rodrigues, Jorge J., Sorenson, Martha M., Smillie, Lawrence B., Silva, Jerson L.
Format: Journal Article
Language:English
Published: United States National Academy of Sciences of the United States of America 01-10-1996
National Acad Sciences
Subjects:
Animals
Atmospheric pressure
Biochemistry
Calcium - physiology
Calcium-Binding Proteins - chemistry
Calcium-Binding Proteins - ultrastructure
Chickens
Cold Temperature
Enthalpy
Entropy
Fluorescence
Hydrostatic Pressure
Low temperature
Mutagenesis, Site-Directed
Pollutant emissions
Protein Conformation
Solubility
Surface areas
Thermodynamics
Troponin C - chemistry
Troponin C - ultrastructure
Water pressure
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Summary:Calcium binding to the N-domain of troponin C initiates a series of conformational changes that lead to muscle contraction. Calcium binding provides the free energy for a hydrophobic region in the core of N-domain to assume a more open configuration. Fluorescence measurements on a tryptophan mutant (F29W) show that a similar conformational change occurs in the absence of Ca$^{2+}$ when the temperature is lowered under pressure. The conformation induced by subzero temperatures binds the hydrophobic probe bis-aminonaphthalene sulfonate, and the tryptophan has the same fluorescence lifetime (7 ns) as in the Ca$^{2+}$-bound form. The decrease in volume ($\Delta $V = -25.4 ml/mol) corresponds to an increase in surface area. Thermodynamic measurements suggest an enthalpy-driven conformational change that leads to an intermediate with an exposed N-domain core and a high affinity for Ca$^{2+}$.
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ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.93.20.10642