Feng, H.-Z. | bioRxiv Science

bioRxiv2025

Thin Filament Interaction and Ca2+-Desensitization Effect of the C-Terminal End Peptide of Cardiac Troponin T Where Loss of Function Mutations Cause Hypertrophic Cardiomyopathy

BackgroundTroponin T (TnT) is the tropomyosin (Tm)-binding subunit of troponin with a central role in regulating cardiac 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. Conformational modulation by proteolytic removal of the N-terminal variable region of cardiac TnT (cTnT-ND) in adaptation to inotropy-afterload mismatch enhances the function of Tm-binding site 3 to adjust ventricular contractile kinetics and sustain stroke volume. Mutations in this segment of cTnT cause overactivation of cardiac muscle and hypertrophic cardiomyopathy (HCM). MethodsThe C-terminal end 14 amino acid peptide of cTnT (cTnT-C14) was analyzed for interactions with Tm, F-actin, and F-actin-Tm thin filament using localized surface plasmon resonance (LSPR). Wild-type and HCM mutant cTnT-C14 peptides were used to treat skinned cardiac muscle strips from wild-type and cTnT-ND transgenic mice to assess the effect on Ca{superscript 2}- activation of contraction. ResultscTnT-C14 peptide showed saturable binding to Tm and F-actin in LSPR with physiological affinity, which is significantly impaired by HCM mutation R278C, K280N or R286C. Treatment of wild-type mouse cardiac muscle strips with cTnT-C14 peptide produced a Ca2+- desensitization effect on myofilament activation, which was not seen with cTnT-ND mouse cardiac muscle strips implicating a prior utilization of the same mechanism. The HCM mutant peptides lost this function. ConclusionsThe findings demonstrate the function of the cTnT C-terminal end segment underlying the pathophysiology of the HCM mutations. Its preserved functionality in the form of free peptide presents a drug candidate for the treatment of heart failure.

physiology↗

bioRxiv2023

The Conserved C-terminal End Segment of Troponin T Is A New Tropomyosin-Binding Site Modulating the Kinetics of Cardiac Muscle

Evolved from duplication of a troponin I (TnI)-like ancestor gene, troponin T (TnT) and TnI are two subunits of the troponin complex that regulates the contraction and relaxation of striated muscles. Proteolytic deletion of the evolutionarily added N-terminal variable region of TnT in adaptation to acute myocardial stress restores a conformation like that of the C-terminal end segment of TnI, a tropomyosin (Tm)-binding and inhibitory structure, with an effect on reducing the contractile velocity of cardiac muscle to prolong ejection time and sustain the stroke volume. To investigate the underlying mechanism of this adaptive conditional function of TnT that is known to have two Tm-binding sites, our study localized a conformationally modulated new Tm-binding site in the highly conserved 14 amino acid C-terminal end segment of TnT. Localized surface plasmon resonance data showed that a hypertrophic cardiomyopathy mutation R278C within the C-terminal end segment of TnT alters the tropomyosin binding with direct responses to physiological concentrations of Ca2+. The functions are retained in the form of free peptide with an inhibitory regulatory effect on the contractile and relaxation kinetics of skinned cardiac muscle. In addition to revealing the underlying mechanisms of cTnT-ND adaptation and cardiac TnT C-terminal myopathic mutations, the new findings provide novel insights into the structure-function relationship of TnT in the kinetics of striated muscle contraction and relaxation with broad physiological and pathophysiological implications.

biochemistry↗