Effects of troponin I phosphorylation on conformational exchange in the regulatory domain of cardiac troponil C

Conformational exchange has been demonstrated within the regulatory domain of calcium-saturated cardiac troponin C when bound to the NH2-terminal doma in of cardiac troponin I-(1-80), and cardiac troponin I-(1-80)DD, having se rine residues 23 and 24 mutated to aspartate to mimic the phosphorylated fo rm of the protein. Binding of cardiac troponin I-(1-80) decreases conformat ional exchange for residues 29, 32, and 34. Comparison of average transvers e cross correlation rates show that both the NH2- and COOH-terminal domains of cardiac troponin C tumble with similar correlation times when bound to cardiac troponin I-(1-80). In contrast, the NH2- and COOH-terminal domains in free cardiac troponin C and cardiac troponin C bound cardiac troponin I- (1-80)DD tumble independently. These results suggest that the nonphosphoryl ated cardiac specific NH2 terminus of cardiac troponin I interacts with the NH2-terminal domain of cardiac troponin C.