Cardiac troponin I inhibitory peptide: location of interaction sites on troponin C

Cardiac troponin I(129-149) binds to the calcium saturated cardiac troponin C/troponin I(1-80) complex at two distinct sites. Binding of the first equ ivalent of troponin I(129-149) was found to primarily affect amide proton c hemical shifts in the regulatory domain, while the second equivalent pertur bed amide proton chemical shifts within the D/E linker region. Nitrogen-15 transverse relaxation rates showed that binding the first equivalent of inh ibitory peptide to the regulatory domain decreased conformational exchange in defunct calcium binding site I and that addition of the second equivalen t of inhibitory peptide decreased flexibility in the D/E linker region. No interactions between the inhibitory peptide and the C-domain of cardiac tro ponin C were detected by these methods demonstrating that the inhibitory pe ptide cannot displace cTnI(1-80) from the C-domain. (C) 2000 Federation of European Biochemical Societies.