Key result
Low calcium blocks the rate-limiting first step of two-step myosin-actin binding via TmTnI.
Why the study?
The mechanisms of calcium-dependent regulation of myosin binding to actin involving tropomyosin and troponin interactions require further elucidation through kinetic data and modeling.
The study proposes a two-step model for myosin binding to actin that explains the calcium dependence of the reaction and predicts cooperative calcium binding to TnC.
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Extends flexible-chain model to kinetic data on thin-filament regulation; leaves open validation in intact cardiac muscle.
Geeves et al. (2011) studied this question. Calcium concentration was evaluated on Time course of myosin-S1 binding to actin-Tm-Tn filaments. Myosin binds to actin in two steps, with the first rate-limiting step blocked by TmTnI at low calcium, and a fast, reversible second step controlled by neighboring tropomyosin-troponin units.
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