Structural and functional studies on Troponin I and Troponin C interactions

Troponin I (TnI) peptides (TnI inhibitory peptide residues 104-115, Ip; TnI regulatory peptide resides 1-30, TnI1-30), recombinant Troponin C (TnC) an d Troponin I mutants were used to study the structural and functional relat ionship between TnI and TnC. Our results reveal that an intact central D/E helix in TnC is required to maintain the ability of TnC to release the TnI inhibition of the acto-S1-TMATPase activity. Ca2+-titration of the TnC-TnI1 -30 complex was monitored by circular dichroism. The results show that bind ing of TnI 1-30 to TnC caused a three-folded increase in Ca2+ affinity in t he high affinity sites (III and IV) of TnC. Gel electrophoresis and high pe rformance liquid chromatography (HPLC) studies demonstrate that the sequenc es of the N- and C-terminal regions of TnI interact in an anti-parellel fas hion with the corresponding N- and C-domain of TnC. Our results also indica te that the N- and C-terminal domains of TnI which flank the TnI inhibitory region (residues 104 to 115) play a vital role in modulating the Ca2+-sens itive release of the TnI inhibitory region by TnC within the muscle filamen t. A modified schematic diagram of the TnC/TnI interaction is proposed. J. Cell. Biochem. 83: 33-46, 2001. (C) 2001 Wiley-Liss, Inc.