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Troponin is a component of thin filaments (along with actin and tropomyosin), and is the protein complex to which calcium binds to trigger the production of muscular force. Troponin has three subunits, TnC, TnI, and TnT, each playing a role in force regulation. [citation needed].
Troponin C is a protein which is part of the troponin complex. It contains four calcium-binding EF hands , although different isoforms may have fewer than four functional calcium-binding subdomains. It is a component of thin filaments , along with actin and tropomyosin .
Troponin I is a cardiac and skeletal muscle protein family. It is a part of the troponin protein complex, where it binds to actin in thin myofilaments to hold the actin-tropomyosin complex in place. Troponin I prevents myosin from binding to actin in relaxed muscle. When calcium binds to the troponin C, it causes conformational changes which ...
The calcium sensitizer, levosimendan, is purported to bind to troponin C, but only weak or inconsistent binding has been detected, [57] [58] [59] precluding any structure determination. In contrast, levosimendan inhibits type 3 phosphodiesterase with nanomolar affinity, [ 60 ] so its biological target is controversial.
Figure 1: Calcium binding to troponin, exposes sites on the actin filaments, to which myosin binds. Using ATP, myosin moves the actin along. The myosin releases the actin, resets itself and binds to another actin binding site. The increase in Ca 2+, produced by CICR, now does two things.
Troponin (Tn), is a key protein complex in the regulation of striated muscle contraction, composed of three subunits. The TnI subunit inhibits actomyosin ATPase , the TnT subunit binds tropomyosin and TnC, while the TnC subunit binds calcium and overcomes the inhibitory action of the troponin complex on actin thin filaments .
Caldesmon binds to actin, tropomyosin, calmodulin, and myosin, of which its interactions with actin are most important. The binding of caldesmon is strongly influenced by tropomyosin. Caldesmon is an inhibitor of actinomyosin ATPase and motility, and both actin binding and caldesmon inhibition are greatly enhanced in the presence of tropomyosin.
Cardiac muscle troponin T (cTnT) is a protein that in humans is encoded by the TNNT2 gene. [5] [6] Cardiac TnT is the tropomyosin-binding subunit of the troponin complex, which is located on the thin filament of striated muscles and regulates muscle contraction in response to alterations in intracellular calcium ion concentration.