Modulation of the interaction between the two halves of troponin C by the other troponin subunits.
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 Ca2+-dependent transition. The midpoints of such spectral changes occur at pCa approximately equal to 6, suggesting that the conformational change of TnT and TnI is induced by Ca2+ 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 Ca2+ 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.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D008670:Metals / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D014336:Troponin / Q000032:analysis*; D019209:Troponin C; D014364:Tryptophan
D008670:Metals; D014336:Troponin; D019209:Troponin C; D014364:Tryptophan; D002118:Calcium