The main protein found in muscle tissue is myosin. Myosin works in conjunction with another protein called actin to facilitate muscle contraction. Together, these proteins form myofibrils, which are the basic units of muscle fibers. When a muscle is stimulated to contract, the interaction between actin and myosin filaments allows the muscle to shorten, thus producing movement. This mechanism is vital for various bodily functions, including locomotion and maintaining posture. The myosin protein is also involved in the energy conversion process, using ATP (adenosine triphosphate) to fuel contractions.