Decreased ATPase Activity and Increased Calcium Sensitivity in Myofibrils with E180G α-Tropomyosin Missense Mutation
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Heart disease is a common affliction that affects the quality of life and is the leading cause of death in the US. Familial hypertrophic cardiomyopathy (FHC), which affects 1 in 5000 individuals, is caused by several mutations, some of which occur in α-tropomyosin. Tropomyosin (Tm) is an integral contractile protein of the sarcomere, which is the functional unit of the heart that regulates its contractions and therefore affects heart contractility when mutated. E180G is one such point mutation that improves systolic function while impairing diastolic function, which causes the heart to hypertrophy and can lead to sudden death because the ability of actin to bind to myosin is compromised. The E180G mutation increases actin filament velocity, calcium sensitivity, and Tm flexibility. This study, the first of its kind, focused on the ATPase activity and calcium sensitivity of cardiac myofibrils regulated by the α-tropomyosin E180G mutation as compared to non-transgenic (NTG)α-tropomyosin. ATPase assays were performed on myofibril samples prepared from mice hearts to quantify the number of contractions in a sarcomere, as approximately one ATP is split per contraction.