Structural and kinetic characterisation of cardiomyopathy associated mutations in troponin C

Cardiovascular diseases are the leading cause of illness and death worldwide. Many heart diseases are due to the impairment of cardiac regulatory mechanisms such as TnC Ca2+- mediated regulation of cardiac muscle contraction. To date a number of Troponin C mutations have been linked to several cardiomyopathies diseases. In this thesis, we aimed to investigate the following troponin C mutations Y5H, A8V, A31S, E59D, D75Y, C84Y, D145E, and I148V which have been shown to cause familial hypertrophic (HCM) and dilated (DCM) cardiomyopathies. We used various structural, biochemical and kinetic methods to assess the impact of these mutations on troponin function and structure. Transient kinetics were used to assess the effect of these mutations on the equilibrium distribution and kinetics of transitions between different thin filament regulatory states. Overall, TnC mutations had little impact on the secondary structure of TnC however HSQC experiments revealed both local and long range structural changes. Our data revealed that cTnC mutations affected various interactions between thin filament components including the interaction of troponin complex with tropomyosin and actin-tropomyosin More importantly all TnC mutations reduced the proportion of the thin filament in the blocked state and the rate constant of Ca2+ dissociation from thin filaments. These findings suggest that mutations in TnC have the potential to affect several allosteric transitions. Consequently, while changes in steps critical for muscle relaxation have been found, mutations in TnC have the potential to affect more than one step in the allosteric network of interactions involved in the regulation of muscle contraction.