Open AccessModulation of the interaction between the two halves of troponin C by the other troponin subunits
Author(s) -
WANG ChihLueh Albert,
GERGELY John
Publication year - 1986
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1986.tb09383.x
Subject(s) - troponin c , troponin complex , troponin i , biophysics , chemistry , troponin , electron paramagnetic resonance , fluorescence , binding site , conformational change , crystallography , biochemistry , stereochemistry , nuclear magnetic resonance , biology , medicine , physics , quantum mechanics , myocardial infarction
The interactions between troponin subunits have been studied by intrinsic fluorescence and electron spin resonance (ESR) spectroscopy. The tryptophan fluorescence of troponin T (TnT) and troponin I (TnI) when complexed with troponin C (TnC) undergoes a Ca 2+ ‐dependent transition. The midpoints of such spectral changes occur at pCa ∼ 6, suggesting that the conformational change of TnT and Tnl is induced by Ca 2+ binding to the low‐affinity sites of TnC. When TnC is labelled at Cys‐98 with a maleimide spin probe (MSL), the spin signal is sensitive to Ca 2+ binding to both the high and the low‐affinity sites of TnC in the presence of either or both of the other two troponin subunits. Since Cys‐98 is located in the vicinity of one of the high‐affinity sites, these results are indicative of a long‐range interaction between the two halves of the TnC molecule. Our earlier kinetic studies [Wang, C.‐L. A., Leavis, P. C. & Gergely, J. (1983) J. Biol. Chem. 258 , 9175–9177] have shown such interactions in TnC alone. Since the ESR spectral change associated with metal binding to the low‐affinity sites is only observed when MSL‐TnC is complexed with TnT and/or TnI, this long‐range interaction within TnC appears to be mediated through the other troponin subunits.