Which protein is primarily involved in the sliding filament model of muscle contraction?

The sliding filament model of muscle contraction centers on the interaction between two primary proteins: actin and myosin. Myosin is the motor protein responsible for generating force during muscle contraction. When a muscle fiber is activated, myosin heads bind to specific sites on the actin filaments to form cross-bridges. This interaction leads to the myosin heads pulling the actin filaments closer together, resulting in the shortening of the muscle fiber.

The sarcomere, which is the fundamental unit of muscle contraction, is composed of organized filaments of actin and myosin. As the myosin heads move—powered by ATP hydrolysis—they effectively "slide" the actin filaments toward the center of the sarcomere. This sliding action is what ultimately leads to muscle contraction according to the sliding filament model. Therefore, myosin plays a crucial role as the active motor component that facilitates this process.

While actin provides the filaments that slide, and proteins like tropomyosin and troponin regulate the interaction between actin and myosin, it is myosin that directly powers the contraction through its ability to bind to actin and perform mechanical work. Thus, myosin is primarily involved in the sliding filament model of muscle contraction.