Inverted Formin 2 (INF2)

Actin filaments grow only when actin monomers have access to the fast-growing barbed end of the filament. The geometry of the filament network depends on the actions of the ARP2/3 complex and members of the formin family, such as INF2. The ARP2/3 complex binds to the sides of preexisting filaments and nucleates filaments whose barbed ends are quickly blocked by capping proteins, producing brush-like structures, such as those found at the leading edges of crawling cells. In contrast, formins bind to the barbed ends of growing filaments and protect them from capping, creating long filaments that can be cross-linked into bundles, such as those found in actin cables of yeast. Interaction of formins with actin barbed ends occurs through the formin homology-2 (FH2) domain.