April 27, 2017
Troponin, which is also known as the Troponin complex, is a combination of 3 proteins namely Troponin C, Troponin I, and Troponin T which are required for muscle contraction of skeletal muscles and cardiac muscles. However it does not play any role in smooth muscles. However, the difference between the 2 muscles is that Troponin C in skeletal muscle has 4 four calcium ion-binding sites, while in cardiac muscle there are only 3 calcium ion-binding sites.
Physiology- the muscle contraction in cardiac muscles and skeletal muscles depends on the concentration of calcium ions in the intracellular matrix. When there is increase in calcium ion concentration, the muscle contracts and when the concentration falls, the muscles relax. Troponin is bound to muscle protein tropomyosin and is located in the grooves between the actin filaments of muscle tissue. Under resting condition, tropomyosin blocks the active sites on actin and prevents formation of myosin cross bridge required for contraction. When the muscle is stimulated, calcium channels open and calcium ions are released into the sarcoplasm. Calcium binds to Troponin and changes its configuration due to which the active sites on myosin are exposed. Then actin myosin cross bridge is formed and muscle contraction occurs.
The functions of different subunits of Troponin are -Troponin C attaches itself to calcium ions to bring about a conformational change in TnI; Troponin T attaches to tropomyosin and interlocks to create Troponin-tropomyosin complex; Troponin I binds to actin and holds the Troponin-tropomyosin complex in place