Myosin was first isolated from mammalian skeletal muscle tissue. Myosin is motor protein and actin filaments are tracks, along which myosin show movement. Myosis have different major classes. Myosins have two classes. Each class has its own specialization functions. Interaction of myosin with actin show a special form of movement called as “contraction”.
Myosin I and Myosin II, are most abundant proteins, present in nearly all eukaryotic cells. All myosins are composed of one or two identical heavy chains and a variety of low molecular weight (light) Chains. The each heavy chain has three structurally and functionally differs domains. A globular head domain is present at N-termines, contains actin and ATP binding sites. The head hydrolyzes ATP. By the energy of hydrolyzed ATP myosin filaments walk towards the end of an actin filament. The head is followed by a -helical reck region. Which associates with light chains and show regulation of the activity of the head domain. The tail domain has the binding sites which allow the molecules to polymerize into bipolar filaments and determine the specific activities of a particular myosin. The tail-tail interactions forms large bipolar filaments, that contains several myosin heads.
Many other types of myosin I, III, IV, XIV are also found in non-muscle cells. Myosins may be involved in a variety of other kinds of cell movements and vesicles transport, Phagocytosis, extension of pseudopodia in amoeba cell locomotion etc.