ADF/Cofilin family

[1] This dynamic instability is central to actin's role in muscle contraction, cell motility and transcription regulation.

Binding by both cofilin and ADF (destrin) causes the crossover length of the filament to be reduced.

[12] "Older" ADP/ADP-Pi actin filaments free of tropomyosin and proper pH are required for cofilin to function effectively.

[13] As a long-lasting in vivo effect, cofilin recycles older ADP-F-actin, helping cell to maintain ATP-G-actin pool for sustained motility.

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,[13] while cofilin-driven depolymerization takes place after dissociating from the Arp2/3 complex.

[12] In particular, ADF/cofilin promotes disassembly of the filament at the rear of the brush in Xenopus laevis lamellipodia, a protrusion from fibroblast cells characterized by actin networks.

[14] F-actin (filamentous actin) is stabilized when it is bound to ATP due to the presence of a serine on the second subunit of actin that is able to form hydrogen bonds to the last phosphate group in ATP and a nearby histidine attached to the main loop.

When ATP is hydrolyzed to ADP, the serine can no longer form a hydrogen bond to ADP due to the loss of the inorganic phosphate which causes the serine side chain to twist, causing a conformational change in the second subunit.

[2] Actin depolymerization factor is regulated by the phosphorylation of a serine on the C terminus by LIM kinases.

[18] F-actin binds the protein Tropomyosin and actin depolymerizing factor competitively and mutually exclusively.