Actin is a globular protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins.
Actin is the monomeric subunit of microfilaments, one of the three major components of the cytoskeleton, and of thin filaments, which are part of the contractile apparatus in muscle cells. Thus, actin participates in many important cellular functions, including muscle contraction, cell motility, cell division and cytokinesis, vesicle and organelle movement, cell signaling, and the establishment and maintenance of cell junctions and cell shape.
Actin has four main functions in cells : 1)to form the most dynamic one of the three subclasses of the cytoskeleton, which gives mechanical support to cells, and hardwires the cytoplasm with the surroundings to support signal transduction. 2) to allow cell motility. 3) in muscle cells to be the scaffold on which myosin proteins generate force to support muscle contraction. 4) in non-muscle cells it functions as a track for cargo transport myosins, non-conventional myosins, such as myosin V and VI. Non-conventional myosins transport cargo, such as vesicles and organelles, in a directed fashion, using ATP hydrolysis, at a rate much faster than diffusion.