The answer is myosin. Myosin are contractile protein the makes up thick filament. The molecule consists of a tail and two myosin heads which bind to myosin binding sites on actin molecules of thin filaments during muscle contraction. Actin on the other hand are contractile proteins that are the main component of thin filament. Each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction.
