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. Troponin C is encoded by the TNNC1 gene in humans for both cardiac and slow skeletal muscle. The structural domain of cTnC (cCTnC) is anchored to troponin I and T, forming the so-called IT arm, made up of cTnC93-161, cTnI41-135 and cTnT235-286 (in the cardiac complex). cCTnC binds to helical cTnI41-60 via its large hydrophobic patch, stabilizing the Ca2+-bound open conformation of cCTnC and enhancing its affinity for Ca2+ (from Kd = 40 nM to Kd = 3 nM). cTnT235-286 forms a helical coiled coil with cTnI88-135 that binds to the opposite face of cCTnC. The IT arm is anchored to tropomyosin via adjacent segments of cTnT, so it is believed to move as a unit along with tropomyosin throughout the cardiac cycle. In the low calcium environment present during diastole (~100 nM), tropomyosin is anchored into the "blocked" position along the actin thin filament through the binding of the troponin I inhibitory (cTnI128-147) and C-terminal (cTnI160-209) regions. This prevents actin-myosin cross-bridging and effectively shuts off muscle contraction.