1. Actin: This is the primary protein in the thin filament. Actin monomers polymerize to form long chains called F-actin, which twist together to form a double helix.
2. Tropomyosin: This protein wraps around the actin filament and blocks the myosin-binding sites on actin when the muscle is relaxed.
3. Troponin: This protein complex sits on the tropomyosin molecule and has three subunits:
* Troponin T: binds to tropomyosin
* Troponin I: inhibits the interaction between actin and myosin
* Troponin C: binds to calcium ions.
These three molecules work together to regulate muscle contraction. When calcium binds to troponin C, it causes a conformational change in troponin, which moves tropomyosin away from the myosin-binding sites on actin. This allows myosin to bind to actin and initiate the sliding filament mechanism of muscle contraction.
