troponin C

Troponin C is a part of the troponin complex.

The calcium binds to the troponin C present on the actin-containing thin filaments of the myofibrils.

This gene encodes an intracellular calcium-binding protein belonging to the troponin C superfamily.

The first group is the largest and includes the most well-known members of the family such as calmodulin, troponin C and S100B.

Levosimendan exerts its positive inotropic effect by increasing calcium sensitivity of myocytes by binding to cardiac troponin C in a calcium-dependent manner.

Calcium ions bind to troponin C, causing a conformational change in the troponin-tropomyosin complex, and thus allowing myosin head binding sites on F-Actin to be exposed.

This stretches the muscle fibers, increasing the affinity of troponin C to Ca ions causing a greater number of cross-bridges to form within the muscle fibers.

However the RYRs are opened, either through mechanical-gating or CICR, Ca is released from the SR and is able to bind to troponin C on the actin filaments.

Troponin is a complex of three regulatory proteins (troponin C, troponin I and troponin T) that is integral to muscle contraction in skeletal and cardiac muscle, but not smooth muscle.

The stretching of the muscle fibres increases the affinity of troponin C for calcium, causing a greater number of cross-bridges to form within the muscle fibres; this increases the contractile force of the cardiac muscle.

Similarly, gain of function of Na+ and Ca2+ channels results in delayed repolarization, and Ca2+ overload causing increased Ca2+ binding to cardiac troponin C, more actin-myosin interactions and causing an increased contractility, respectively(3).

Under normal circumstances, the tropomyosin sterically obstructs binding sites for myosin on the thin filament; once calcium binds to the troponin C and causes an allosteric change in the troponin protein, troponin T allows tropomyosin to move, unblocking the binding sites.

Upon binding to Ca, this motif may undergo conformational changes that enable Ca-regulated functions as seen in Ca effectors such as calmodulin (CaM) and troponin C (TnC) and Ca buffers such as calreticulin and calbindin D9k.