Arp2/3 complex

Arp2/3 complex is a seven-subunit protein complex that plays a major role in the regulation of the actin cytoskeleton. It is a major component of the actin cytoskeleton and is found in most actin cytoskeleton-containing eukaryotic cells.Two of its subunits, the Actin-Related Proteins ARP2 and ARP3, closely resemble the structure of monomeric actin and serve as nucleation sites for new actin filaments. The complex binds to the sides of existing ('mother') filaments and initiates growth of a new ('daughter') filament at a distinctive 70 degree angle from the mother. Branched actin networks are created as a result of this nucleation of new filaments. The regulation of rearrangements of the actin cytoskeleton is important for processes like cell locomotion, phagocytosis, and intracellular motility of lipid vesicles. Arp2/3 complex is a seven-subunit protein complex that plays a major role in the regulation of the actin cytoskeleton. It is a major component of the actin cytoskeleton and is found in most actin cytoskeleton-containing eukaryotic cells.Two of its subunits, the Actin-Related Proteins ARP2 and ARP3, closely resemble the structure of monomeric actin and serve as nucleation sites for new actin filaments. The complex binds to the sides of existing ('mother') filaments and initiates growth of a new ('daughter') filament at a distinctive 70 degree angle from the mother. Branched actin networks are created as a result of this nucleation of new filaments. The regulation of rearrangements of the actin cytoskeleton is important for processes like cell locomotion, phagocytosis, and intracellular motility of lipid vesicles. The Arp2/3 complex was named after it was identified in 1994 by affinity chromatography from Acanthamoeba castellanii, though it had been previously isolated in 1989 in a search for proteins that bind to actin filaments in Drosophila melanogaster embryos. It is found in most eukaryotic organisms, but absent from a number of Chromalveolates and plants. Many actin-related molecules create a free barbed end for polymerization by uncapping or severing pre-existing filaments and using these as actin nucleation cores. However, the Arp2/3 complex stimulates actin polymerization by creating a new nucleation core. Actin nucleation is an initial step in the formation of an actin filament. The nucleation core activity of Arp2/3 is activated by members of the Wiskott-Aldrich syndrome family protein (WASP, N-WASP, WAVE, and WASH proteins). The V domain of a WASP protein interacts with actin monomers while the CA region associates with the Arp2/3 complex to create a nucleation core. However, de novo nucleation followed by polymerization is not sufficient to form integrated actin networks, since these newly synthesized polymers would not be associated with pre-existing filaments. Thus, the Arp2/3 complex binds to pre-existing filaments so that the new filaments can grow on the old ones and form a functional actin cytoskeleton. Capping proteins limit actin polymerization to the region activated by the Arp2/3 complex, and the elongated filament ends are recapped to prevent depolymerization and thus conserve the actin filament.