Interaction of troponin I and troponin C: 19F NMR studies of the binding of the inhibitory troponin I peptide to turkey skeletal troponin C.
We have used 19F nuclear magnetic resonance spectroscopy to study the interaction of the inhibitory region of troponin (TnI) with apo- and calcium(II)-saturated turkey skeletal troponin C (TnC), using the synthetic TnI analogue N alpha-acetyl[19FPhe106]TnI(104-115)amide. Dissociation constants of Kd = (3.7 +/- 3.1) x 10(-5) M for the apo interaction and Kd = (4.8 +/- 1.8) x 10(-5) M for the calcium(II)-saturated interaction were obtained using a 1:1 binding model of peptide to protein. The 19F NMR chemical shifts for the F-phenylalanine of the bound peptide are different from the apo- and calcium-saturated protein, indicating a different environment for the bound peptide. The possibility of 2:1 binding of the peptide to Ca(II)-saturated TnC was tested by calculating the fit of the experimental titration data to a series of theoretical binding curves in which the dissociation constants for the two hypothetical binding sites were varied. We obtained the best fit for 0.056 mM less than or equal to Kd1 less than or equal to 0.071 mM and 0.5 mM less than or equal to Kd2 less than or equal to 2.0 mM. These results allow the possibility of a second peptide binding site on calcium(II)-saturated TnC with an affinity 10- to 20-fold weaker than that of the first site.
Campbell
A P
AP
Department of Biochemistry, University of Alberta, Edmonton, Canada.
Cachia
P J
PJ
Sykes
B D
BD
D000818:Animals; D002118:Calcium / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D014336:Troponin / Q000737:chemistry* / Q000378:metabolism; D019209:Troponin C; D019210:Troponin I; D014422:Turkeys
D014336:Troponin; D019209:Troponin C; D019210:Troponin I; D002118:Calcium