Human Cardiac Troponin I

The contraction of skeletal and cardiac muscle (striated muscle) is enabled when calcium ions bind to troponin, which causes a conformational change and pulls the tropomyosin off the myosin-binding sites on the actin filaments. The uncovering of the binding sites allows the myosin heads to bind the actin, forming a cross-bridge. Once ATP hydrolysis occurs, the power stroke needed for a muscle contraction pulls the actin and myosin filaments closer to the M line, shortening the sarcomere. Troponin is a trimeric complex of three proteins (I, T, and C), each with a different function that allows troponin to perform its role relating to muscle contraction.

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Function

Each of the protein subunits has an individualized function related to troponin’s role in muscle contraction. Troponin I (TnI) binds to the actin filament, inhibiting the ATPase activity from the actin-myosin binding.^[3] Troponin T (TnT) attaches to tropomyosin, anchoring it to the actin and forming the Tn-tropomyosin complex.^[3] Troponin C (TnC) binds to calcium ions, inducing the conformational changes in TnI and uncovering the myosin-binding sites blocked by the tropomyosin.^[3] Through this process, cross-bridge cycling occurs so that a power stroke can activate the muscle contraction.

Disease

Relevance

Structural highlights

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