Role of the C-terminus mobile domain of cardiac troponin I in the regulation of thin filament activation in skinned papillary muscle strips

• Published in: Archives of biochemistry and biophysics Vol. 648; pp. 27 - 35
• Main Authors: Bohlooli Ghashghaee, Nazanin, Li, King-Lun, Solaro, R. John, Dong, Wen-Ji
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-06-2018
• Subjects: Cardiac troponin I; Cross-bridge; Förster resonance energy transfer (FRET); Length dependent activation; Mobile domain truncation; Troponin; cTnI; Length dependent activation; DTT; N-cTnC; Cross-bridge; cTnC; LDA; BDM; Förster resonance energy transfer (FRET); EGTA; Vanadate; BES; Troponin; Cardiac troponin I; HWHM; Mobile domain truncation; cTnI-MD; cTnT; SL; FRET; cTnI(WT)
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/j.abb.2018.04.014

The C-terminus mobile domain of cTnI (cTnI-MD) is a highly conserved region which stabilizes the actin-cTnI interaction during the diastole. Upon Ca2+-binding to cTnC, cTnI-MD participates in a regulatory switching that involves cTnI to switch from interacting with actin toward interacting with the Ca2+-regulatory domain of cTnC. Despite many studies targeting the cTnI-MD, the role of this region in the length-dependent activation of cardiac contractility is yet to be determined. The present study investigated the functional consequences of losing the entire cTnI-MD in cTnI(1–167) truncation mutant, as it was exchanged for endogenous cTnI in skinned rat papillary muscle fibers. The influence of cTnI-MD truncation on the extent of the N-domain of cTnC hydrophobic cleft opening and the steady-state force as a function of sarcomere length (SL), cross-bridge state, and [Ca2+] was assessed using the simultaneous in situ time-resolved FRET and force measurements at short (1.8 μm) and long (2.2 μm) SLs. Our results show the significant role of cTnI-MD in the length dependent thin filament activation and the coupling between thin and thick filament regulations affected by SL. Our results also suggest that cTnI-MD transmits the effects of SL change to the core of troponin complex.
•cTnI(1–167) perturbs the thin filament-based regulatory mechanisms of length dependent activation.•cTnI(1–167) uncouples the thin and thick filament-based regulations of length dependent activation.•cTnI(1–167) promotes the opening of the N-cTnC hydrophobic cleft at short SL.•cTnI(1–167) diminishes the sarcomere length-induced opening of N-cTnC.•The cTnI(1–167) effects on thin filament activation are more pronounced at short SL.