Figure 2.
Regulation of thin filaments. The thin filament proteins tropomyosin and troponin regulate the contraction of striated muscle. Tropomyosin is an elongated, coiled-coil molecule that binds to the surface of the thin actin filament. Troponin comprises three subunits—troponin T (TnT), which binds to tropomyosin; troponin I (TnI), which binds to both actin and tropomyosin; and troponin C (TnC), which confers Ca2+ sensitivity to the system. The relative position of these proteins on the actin filament is schematized.