The functional significance of the last 5 residues of the C-terminus of cardiac troponin I

The C-terminal region of cardiac troponin I (cTnI) is known to be important in cardiac function, as removal of the last 17 C-terminal residues of human cTnI has been associated with myocardial stunning. To investigate the C-terminal region of cTnl, three C-terminal deletion mutations in human cTnl were generated: Delta 1 (deletion of residue 210), Delta 3 (deletion of residues 208-210), and Delta 5 (deletion of residues 206-210). Mammalian two-hybrid studies showed that the interactions between cTnl mutants and cardiac troponin C (cTnC) or cardiac troponin T (cTnT) were impaired in Delta 3 and Delta 5 mutants when compared to wild-type cTnl. Troponin complexes containing 2-[4'-(iodoacetamido) anilinol naphthalene-6-sulfonic acid (IAANS) labeled cTnC showed that the troponin complex containing cTnI Delta 5 had a small increase in Ca2+ affinity (P < 0.05); while the cTnl Delta 1- and Delta 3 troponin complexes showed no difference in Ca2+ affinity when compared to wild-type troponin. In vitro motility assays showed that all truncation mutants had increased Ca2+ dependent motility relative to wild-type cTnI. These results suggest that the last 5 C-terminal residues of cTnI influence the binding of cTnl with cTnC and cTnT and affect the Ca2+ dependence of filament sliding, and demonstrate the importance of this region of cTnI. (C) 2016 Elsevier Inc. All rights reserved.