Which proteins are responsible for muscle contraction?

Muscle contraction is primarily facilitated by two types of proteins known as actin and myosin. Actin is a thin filament that provides a track for the movement of myosin, which is a thick filament that has the ability to pull on actin filaments. This interaction between actin and myosin is fundamental for muscle contraction, occurring through a mechanism known as the sliding filament theory. When a muscle is stimulated to contract, myosin heads bind to actin filaments, creating cross-bridges; then, through a series of conformational changes powered by ATP, the myosin pulls the actin filaments closer together, resulting in muscle shortening and contraction.

Other proteins like troponin and tropomyosin also play crucial roles in regulating muscle contraction; however, they do not actively contract the muscle themselves. Instead, they help control the interaction between actin and myosin by regulating access to the binding sites on actin. Collagen and elastin are structural proteins found in connective tissues and are not involved in muscle contraction. Similarly, keratin and fibrin serve different functions, such as forming hair and nails or blood clotting, rather than participating directly in the muscle contraction process. Therefore, actin and myosin are the primary