Ca2+ and conformational changes

Elevated Ca2+ concentration causes a conformational change in two accessory proteins, tropomyosin (TM) and the troponin (TN) complex. In the absence of Ca2+ tropomyosin, which is a rope like protein, covers up the binding site for myosin on the actin filament. In the presence of Ca2+ the myosin binding site is exposed. Troponin complex is composed of 3 molecules, TH-T, TN-I and TN-C. TN-C is the calcium binding subunit of the complex. Association of Ca2+ to TN-C causes a conformational change which ultimately results in a conformational change in tropomyosin.