MEDICAL PHYSIOLOGY

Detailed explanation-1: -Troponin plays a central role in the calcium-regulation of muscle contraction: Troponin is the sole calcium-binding component of thin filaments (actin-tropomyosin-troponin complex) of striated muscles.

Detailed explanation-2: -The muscle protein troponin-C (TnC) contains four calcium-binding sites arranged as a pair of two-site domains. In the absence of calcium the C-terminal domain, containing calcium-binding sites III and IV, is mostly unfolded.

Detailed explanation-3: -Each heartbeat is triggered by a pulse of intracellular calcium ions which bind to troponin on the actin-containing thin filaments of heart muscle cells, initiating a change in filament structure that allows myosin to bind and generate force.

Detailed explanation-4: -Troponin I (TnI), the inhibitory subunit, binds actin in the relaxed state, thereby preventing muscle contraction by inhibiting the ATPase activity of actomyosin. Troponin T (TnT) is involved in the attachment of the troponin complex to the thin filament, binding tropomyosin and actin.

Detailed explanation-5: -Troponin C (TnC; 18 kDa) is the calcium-binding component of the contractile apparatus and upon binding intracellular Ca2 + ions induces a conformational change in the troponin–tropomyosin complex, reducing TnI inhibition of the actinomysin ATPase and allowing muscle contraction to occur [18].