What happens when calcium binds to troponin C?

The binding of calcium ions to troponin C triggers vertebrate striated (skeletal or cardiac) muscle contraction through a series of interactions involving the regulatory proteins including tropomyosin and troponin that regulate the interaction between actin and myosin (1) that ultimately generates force by sliding (2.

Does calcium change the shape of troponin?

When calcium binds to troponin, the troponin changes shape, removing tropomyosin from the binding sites.

What is the purpose of calcium binding to troponin?

Upon binding calcium, troponin moves tropomyosin away from the myosin-binding sites on actin (bottom), effectively unblocking it.

What happens when Ca binding causes a change in the conformation of troponin?

Ca2+ binding to the regulatory site(s) of TnC triggers a series of conformational changes in the troponin (Tn) complex, allows tropomyosin to move along the actin filaments and allows actin to interact with myosin to produce force [1].

How does calcium unbind from troponin?

Unbinding of calcium from TN-C induces a conformational change in the troponin complex leading, once again, to TN-I inhibition of the actin binding site. At the end of the cycle, a new ATP binds to the myosin head, displacing the ADP, and the initial sarcomere length is restored.

Which is the motif that binds ca2+ in the protein troponin C?

Troponin C has four Ca2+-binding sites, termed sites I, II, III, and VI from the N-terminus, each of which consists of a Ca2+-coordinating loop rich in acidic residues flanked with two α-helical segments (E-F-hand motif).

What changes shape upon binding with calcium ions?

The calcium ions bind to the troponin, changing the shape of the troponin-tropomyosin complex such that the actin binding sites are uncovered. As soon as myosin binds to actin, the cocked head of myosin releases sliding the actin fiber.

How do calcium ions affect troponin?

The calcium that enters the heart cell through the calcium ion channel activates the ryanodine receptor to release enough calcium from the sarcoplasmic reticulum to initiate heart muscle contraction. This is done by binding to another structure, named troponin, inside the heart muscle cell.

Does troponin C bind to actin?

Troponin C, also known as TN-C or TnC, is a protein that resides in the troponin complex on actin thin filaments of striated muscle (cardiac, fast-twitch skeletal, or slow-twitch skeletal) and is responsible for binding calcium to activate muscle contraction.

What does calcium bind to in muscle contraction?

(1) Calcium binds to troponin C, causing the conformational shift in tropomyosin that reveals myosin-binding sites on actin.