Troponin

Troponin is a complex of three regulatory proteins (troponin C, troponin I, and troponin T) that is integral to muscle contraction in skeletal muscle and cardiac muscle, but not smooth muscle. Bundles of filaments, made up of myosin and actin, create these muscle contractions. It is a component of thin filaments (along with actin and tropomyosin).

Structure

Troponin is attached to the protein tropomyosin and lies within the groove between actin filaments in muscle tissue. In a relaxed muscle, tropomyosin blocks the attachment site for the myosin crossbridge, thus preventing contraction. When the muscle cell is stimulated to contract by an action potential, calcium channels open in the sarcoplasmic reticulum and release calcium into the sarcoplasm. Some of this calcium attaches to troponin, which causes it to change shape, exposing binding sites for myosin (active sites) on the actin filaments.

Function

Troponin is found in both skeletal muscle and cardiac muscle, but the specific versions of troponin differ between types of muscle. The troponin complex is integral for muscle contraction. It is made up of three subunits: troponin I, troponin T, and troponin C. Each subunit serves a unique function.

Clinical significance

Troponin levels in the blood can become elevated if an event such as a heart attack causes damage to the heart muscle. Because of this, troponin tests are used to diagnose heart attacks and other conditions that damage the heart muscle.

See also

• Myosin
• Actin
• Tropomyosin
• Muscle contraction
• Heart attack

References

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