Fig. 3

Structure and arrangement of cardiac thin filament proteins in the absence (off) and presence (on) of Ca²⁺. Shapes of the proteins are drawn primarily based on evidence from the work by Takeda et al. [15]. Upon Ca²⁺ binding to TnC, the C-terminus region of TnI dissociates from actin, allowing for Tm movement and, consequently, myosin binding to actin. Arrows indicate relative movements of Tm position in diastole and systole. C COOH terminus, N NH₂ terminus. The equilibrium between the “off” state and the “on” state is a function of [Ca²⁺]_i