The intrinsically disordered carboxy-terminus of troponin-T binds to troponin-C to modulate myocardial force generation
Jamie R. Johnston, Maicon Landim-Vieira, Mayra A Marques, Guilherme A. P. de Oliveira, David Gonzalez-Martinez, Adolfo H. Moraes, Huan He, Anwar Iqbal, Yael Wilnai, Einat Birk, Nili Zucker, Jerson L. Silva, P Bryant Chase, Jose Renato Pinto
Journal of Biological Chemistry
Aberrant regulation of myocardial force production represents an early biomechanical defect associated with sarcomeric cardiomyopathies, but the molecular mechanisms remain poorly defined. Here, we evaluated the pathogenicity of a previously unreported sarcomeric gene variant identified in a pediatric patient with sporadic dilated cardiomyopathy and determined a molecular mechanism. Trio whole exome sequencing revealed a de novo missense variant in TNNC1 that encodes a p.Ile4Met substitution in the amino-terminal helix of cardiac troponin C (cTnC). Reconstitution of this human cTnC variant into permeabilized porcine cardiac muscle preparations significantly decreases the magnitude and rate of isometric force generation at physiological Ca2+-activation levels. Computational modeling suggests that this inhibitory effect can be explained by a decrease in the rates of cross-bridge attachment and detachment. For the first time, we show that cardiac troponin T (cTnT), in part through its intrinsically disordered carboxy-terminus, directly binds to wild-type cTnC and find that this cardiomyopathic variant displays tighter binding to cTnT. Steady-state fluorescence and nuclear magnetic resonance spectroscopy studies suggest that this variant propagates perturbations in cTnC structural dynamics to distal regions of the molecule. We propose that the intrinsically disordered carboxy-terminus of cTnT directly interacts with regulatory N-domain of cTnC to allosterically modulate Ca2+ activation of force, perhaps by controlling the troponin I switching mechanism of striated muscle contraction. Alterations in cTnC-cTnT binding may compromise contractile performance and trigger pathological remodeling of the myocardium.
Fluorescence, Protein structure, Chemical stability, Ligand binding, Biochemistry