Key result
Disease-causing mutations of troponin, particularly the hypertrophic cardiomyopathy mutation Δ14 of TnT, eliminate the inactive-Ca2+-free state and shift the equilibrium to favor the active state.
Why the study?
Saturating Ca 2+ produces a mixture of inactive and active states of the contractile system, making study of individual regulatory states difficult.
Hypertrophic cardiomyopathy-causing mutations like Δ14-TnT reveal that the C-terminal region of Troponin T acts as a brake to limit calcium activation, providing insights into striated muscle regulation.
TnT brake disruption in HCM mutations may inform molecular models; leaves open targeted therapies pending clinical validation.
Striated muscle contraction is inhibited by the actin associated proteins tropomyosin, troponin T, troponin I and troponin C. Binding of Ca 2+ to troponin C relieves this inhibition by changing contacts among the regulatory components and ultimately repositioning tropomyosin on the actin filament creating a state that is permissive for contraction. Several lines of evidence suggest that there are three possible positions of tropomyosin on actin commonly called Blocked, Closed/Calcium and Open or Myosin states. These states are thought to correlate with different functional states of the contractile system: inactive-Ca 2+ -free, inactive-Ca 2+ -bound and active. The inactive-Ca 2+ -free state is highly occupied at low free Ca 2+ levels. However, saturating Ca 2+ produces a mixture of inactive and active states making study of the individual states difficult. Disease causing mutations of troponin, as well as phosphomimetic mutations change the stabilities of the states of the regulatory complex thus providing tools for studying individual states. Mutants of troponin are available to stabilize each of three structural states. Particular attention is given to the hypertrophic cardiomyopathy causing mutation, Δ14 of TnT, that is missing the last 14 C-terminal residues of cardiac troponin T. Removal of the basic residues in this region eliminates the inactive-Ca 2+ -free state. The major state occupied with Δ14 TnT at inactivating Ca 2+ levels resembles the inactive-Ca 2+ -bound state in function and in displacement of TnI from actin-tropomyosin. Addition of Ca 2+ , with Δ14TnT, shifts the equilibrium between the inactive-Ca 2+ -bound and the active state to favor that latter state. These mutants suggest a unique role for the C-terminal region of Troponin T as a brake to limit Ca 2+ activation.
No takes yet. Share an insight, caveat, or question.
Chalovich et al. (2022) conducted a review in Hypertrophic Cardiomyopathy. Troponin mutations (e.g., Δ14 TnT) vs. Wild type troponin was evaluated. Disease-causing mutations of troponin, particularly the hypertrophic cardiomyopathy mutation Δ14 of TnT, eliminate the inactive-Ca2+-free state and shift the equilibrium to favor the active state.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: