Troponin C, fast skeletal muscle (TNNC2)

Troponin C, fast skeletal muscle (TNNC2), is the calcium-binding component of the troponin complex specific to fast-twitch skeletal muscle fibers[2][3][4]. It functions as the primary **calcium sensor** that regulates striated muscle contraction by binding Ca2+ and transmitting conformational changes that relieve inhibition of actin-myosin interaction[1][2][5]. TNNC2 is composed of four EF-hand domains, of which two N-terminal sites are regulatory (binding Ca2+) and two C-terminal sites are structural (often binding Mg2+ in the resting state)[1]. Upon calcium binding, TNNC2 promotes the displacement of tropomyosin on actin filaments, allowing myosin head attachment and muscle contraction[1][2]. Pathogenic variants can cause rare congenital myopathies, but TNNC2 is most widely recognized for its essential physiological role in rapid skeletal muscle force generation[3][4]. While the fast skeletal isoform is not a routine therapeutic target, its homologs in cardiac tissue (cardiac troponin C) are key clinical biomarkers and drug targets[1]. Drugs such as bepridil interact with troponin C to sensitize Ca2+ binding in cardiac muscle, and similar approaches have been proposed for skeletal isoforms but remain experimental[1]. The troponin C, fast skeletal muscle gene is found on chromosome 20 in humans[3][4].

Other names

Troponin C2, fast skeletal typeTNNC2Troponin C, skeletal muscleFAP85CFAP85CMYO15CMYP15MYONRI

Calcium sensitization (stabilizing Ca2+-bound conformation to enhance muscle contraction); Modulation of troponin complex activity on the thin filament