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 (F29W) show that a similar conformational change occurs in the absence of Ca2+ 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 Ca2+-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 Ca2+.
Foguel
D
D
Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Brazil.
Suarez
M C
MC
Barbosa
C
C
Rodrigues
J J
JJ
Sorenson
M M
MM
Smillie
L B
LB
Silva
J L
JL
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000648:ultrastructure*; D002645:Chickens; D003080:Cold Temperature; D019277:Entropy; D006874:Hydrostatic Pressure; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012995:Solubility; D013816:Thermodynamics; D019209:Troponin C / Q000737:chemistry / Q000648:ultrastructure*
D002135:Calcium-Binding Proteins; D019209:Troponin C; D002118:Calcium