Human cardiac-specific troponin I (TnI) is an integral inhibitory protein of cardiac muscle which exists as a complex with troponin C (TnC) and troponin T (TnT). The TnT subunit of troponin binds to tropomyosin to form a troponin-tropomyosin complex, anchored in place by the binding of TnI to actin, within muscle thin filaments. Structural change resulting from the binding of calcium to specific sites on the regulatory TnC subunit, releases the inhibitory region of TnI from actin, enabling the attachment of the molecular motor protein myosin, allowing for muscle contraction and hence movement.