Function
Cofilin is a ubiquitous actin-binding factor required for the reorganization of actin filaments. ADF/Cofilin family members bind G-actin monomers and depolymerize actin filaments through two mechanisms: severing and increasing the off-rate for actin monomers from the pointed end. "Older" ADP/ADP-Pi actin filaments free of tropomyosin and proper pH are required for cofilin to function effectively. In the presence of readily available ATP-G-actin cofilin speeds-up actin polymerization via its actin-severing activity (providing free barbed ends for further polymerization and nucleation by the Arp2/3 complex). As a long-lasting in vivo effect, cofilin recycles older ADP-F-actin, helping cell to maintain ATP-G-actin pool for sustained motility. pH, phosphorylation and phosphoinositides regulate cofilin’s binding and associating activity with actin
The Arp2/3 complex and cofilin work together to reorganize the actin filaments in the cytoskeleton. Arp 2/3, an actin binding proteins complex, binds to the side of ATP-F-actin near the growing barbed end of the filament, causing nucleation of a new F-actin branch, while cofilin-driven depolymerization takes place after dissociating from the Arp2/3 complex. They also work together to reorganize microtubules in order to traffic more proteins by vesicle to continue the growth of filaments.
Cofilin also binds with other proteins such as myosin, tropomyosin, α-actinin, gelsolin and scruin. These proteins compete with cofilin for actin binding. Сofilin also play role in innate immune response.
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