Which motor protein is primarily responsible for muscle contraction?

Muscle contraction is primarily facilitated by myosin, a type of motor protein. Myosin interacts with actin filaments within muscle cells, forming cross-bridges that allow myosin to pull on the actin, resulting in contraction. This process is a crucial component of the sliding filament model, which explains how muscles contract.

Myosin heads bind to specific sites on the actin filaments, undergo conformational changes powered by ATP hydrolysis, and effectively 'walk' along the filaments, pulling them closer together. This action is fundamental to muscle movement, whether in skeletal muscle, cardiac muscle, or smooth muscle.

Other proteins, such as kinesin and dynein, are involved in intracellular transport along microtubules but do not play a direct role in muscle contraction. While actin is also critical to muscle function, as it serves as the structural framework for the interaction with myosin, it is the myosin protein that directly drives the contraction mechanism.