J Mol Cell Cardiol. 2026 Aug;217:29-39. doi: 10.1016/j.yjmcc.2026.05.008. Epub 2026 May 22.
ABSTRACT
Troponin T (TnT), the tropomyosin (Tm)-binding subunit of troponin, plays a central role in regulating striated muscle contractility. The recently identified Tm-binding site 3 in the highly conserved C-terminal end segment of TnT has a troponin I (TnI)-like inhibitory function. A restrictive proteolytic removal of the N-terminal hypervariable region (amino acids 1-71) of cardiac TnT (cTnT-ND) in vivo in adaptation to inotropy-afterload mismatch slows down ventricular end-systolic velocity to increase ejection time and stroke volume through a conformational modulation that enhances the function of Tm-binding site 3. Mutations in this segment of cTnT cause hyperactivation of cardiac muscle and hypertrophic cardiomyopathy (HCM). Here we characterized isolated C-terminal end 14 amino acids (275-288) peptide of cTnT (cTnT-C14) for interactions with Tm, F-actin, and F-actin-Tm thin filament using localized surface plasmon resonance (LSPR). Wild-type cTnT-C14 peptide showed saturable strong binding to Tm and F-actin in LSPR, which is significantly weakened by HCM mutation R278C, K280N or R286C. Contractility studies of permeabilized mouse cardiac muscle strips found that the HCM mutant peptides all lost the known Ca2+-desensitization function of wild-type cTnT-C14 peptide, correlating to the pathogenesis and pathophysiology of HCM. Treatment of cTnT-ND transgenic mouse cardiac muscle with the phenotype of lower than wild-type maximum force production with wild-type cTnT-C14 peptide did not produce additive effect, implicating that cTnT-C14 peptide and cTnT-ND both utilize the Tm-binding site 3 mechanism to reduce maximum activation while free cTnT-C14 peptide does not diminish the effect of cTnT-ND in native thin filament on increasing the overall sensitivity to Ca2+-activation. The functionality of cTnT-C14 in the form of free peptide presents a novel reagent for adjusting contractile kinetics of cardiac muscle and alleviating myofilament hyperactivation.
PMID:42173310 | PMC:PMC13334471 | DOI:10.1016/j.yjmcc.2026.05.008