What is the effect of the troponin complex when Ca2+ binds to it?

When calcium ions (Ca2+) bind to the troponin complex, a significant change occurs in the structure of the troponin-tropomyosin complex. The troponin complex consists of three proteins: troponin C, troponin I, and troponin T. When calcium binds to troponin C, it induces a conformational change in the whole troponin complex, which in turn causes tropomyosin to shift position on the actin filament.

This movement of tropomyosin is crucial because it exposes the myosin binding sites on the actin filaments, allowing for cross-bridge formation between myosin heads and actin filaments. This process is fundamental to the mechanism of muscle contraction, as the myosin heads can now interact with actin to produce force and shorten the muscle fiber. Therefore, the binding of Ca2+ to the troponin complex enables the interaction necessary for muscle contraction by revealing the binding sites on actin.