Molecular basis of calcium-sensitizing and desensitizing mutations of the human cardiac troponin C regulatory domain: a multi-scale simulation study
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Updated: May 16, 2026
Assessment of Myofilament Ca2+ Sensitivity Underlying Cardiac Excitation-contraction Coupling
Published on: August 1, 2016
Peter Michael Kekenes-Huskey1, Steffen Lindert, James Andrew McCammon
1Department of Pharmacology, Center for Theoretical Biological Physics, National Computational Biomedical Resource and Howard Hughes Medical Institute, University of California San Diego, La Jolla, California, United States of America. pkekeneshuskey@ucsd.edu
Abstract:
Troponin C (TnC) is implicated in the initiation of myocyte contraction via binding of cytosolic Ca²⁺ and subsequent recognition of the Troponin I switch peptide. Mutations of the cardiac TnC N-terminal regulatory domain have been shown to alter both calcium binding and myofilament force generation. We have performed molecular dynamics simulations of engineered TnC variants that increase or decrease Ca²⁺ sensitivity, in order to understand the structural basis of their impact on TnC function. We will use the distinction for mutants that are associated with increased Ca²⁺ affinity and for those mutants with reduced affinity. Our studies demonstrate that for GOF mutants V44Q and L48Q, the structure of the physiologically-active site II Ca²⁺ binding site in the Ca²⁺-free (apo) state closely resembled the Ca²⁺-bound (holo) state. In contrast, site II is very labile for LOF mutants E40A and V79Q in the apo form and bears little resemblance with the holo conformation. We hypothesize that these phenomena contribute to the increased association rate, k(on), for the GOF mutants relative to LOF. Furthermore, we observe significant positive and negative positional correlations between helices in the GOF holo mutants that are not found in the LOF mutants. We anticipate these correlations may contribute either directly to Ca²⁺ affinity or indirectly through TnI association. Our observations based on the structure and dynamics of mutant TnC provide rationale for binding trends observed in GOF and LOF mutants and will guide the development of inotropic drugs that target TnC.
Insights
Mutations in cardiac Troponin C (TnC) alter calcium sensitivity and myocyte contraction. Molecular dynamics simulations reveal distinct structural changes in gain-of-function (GOF) and loss-of-function (LOF) TnC mutants, explaining altered calcium binding and guiding inotropic drug development.
Area of Science:
- Cardiovascular Physiology
- Molecular Biology
- Biophysics
Background:
- Cardiac Troponin C (TnC) regulates myocyte contraction by binding calcium (Ca²⁺) and interacting with Troponin I.
- Mutations in the TnC N-terminal regulatory domain can alter Ca²⁺ sensitivity and force generation.
- Understanding these structural changes is crucial for developing targeted therapies.
Purpose of the Study:
- To investigate the structural basis of altered Ca²⁺ sensitivity in engineered TnC variants using molecular dynamics (MD) simulations.
- To differentiate the structural dynamics between gain-of-function (GOF) and loss-of-function (LOF) TnC mutants.
- To provide a structural rationale for observed binding trends and guide the development of inotropic drugs.
Main Methods:
- Molecular dynamics (MD) simulations of engineered TnC variants with altered Ca²⁺ sensitivity.
- Analysis of Ca²⁺ binding site II conformation in both Ca²⁺-free (apo) and Ca²⁺-bound (holo) states.
- Examination of positional correlations between helices in different TnC mutant conformations.
Main Results:
- GOF mutants (V44Q, L48Q) exhibited a stable Ca²⁺-binding site II structure in the apo state, resembling the holo state.
- LOF mutants (E40A, V79Q) showed a labile apo site II conformation, differing significantly from the holo state.
- GOF holo mutants displayed unique inter-helical positional correlations absent in LOF mutants, potentially impacting Ca²⁺ affinity or TnI interaction.
Conclusions:
- The structural stability of the Ca²⁺-binding site in apo-TnC correlates with Ca²⁺ affinity and functional outcomes (GOF vs. LOF).
- Observed inter-helical dynamics in GOF mutants may directly influence Ca²⁺ binding or indirectly affect Troponin I association.
- These findings offer a structural framework for understanding TnC mutations and developing novel inotropic agents targeting TnC.
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