Troponin C type 1

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.

Structure

Cardiac troponin C (cTnC) is a 161-amino acid protein organized into two domains: the regulatory N-terminal domain (cNTnC, residues 1-86), the structural C-terminal domain (cCTnC, residues 93-161), and a flexible linker connecting the two domains (residues 87-92). Each domain contains two EF-hands, Ca²⁺-binding helix-loop-helix motifs exemplified by proteins like parvalbumin. and calmodulin. In cCTnC the two EF-hand motifs constitute two high affinity Ca²⁺-binding sites. that are occupied at all physiologically relevant calcium concentrations. In contrast, only the second EF-hand in cNTnC binds Ca²⁺ with low affinity, while the first EF-hand Ca²⁺-binding site is defunct.