Fig. 6: Working model for regulation of actin dynamics by twinfilin, formin, and CP.

Barbed-end outcomes would depend upon whether barbed ends were free or formin-bound. a Free barbed ends (B) would rapidly get capped by CP (C), followed by CP’s dissociation by twinfilin (T). This would leave twinfilin alone at the filament end, causing its depolymerization. At the same time, cofilin would bind the sides of the aging filament and synergize with cyclase-associated protein (CAP) to initiate the filament’s pointed-end depolymerization. The simultaneous depolymerization at the two ends would result in the complete disassembly of the filament into monomers. b Formin (F) bound barbed ends would get paused by CP to form BFC complexes. Twinfilin’s binding to BFC complexes would cause CP’s dissociation and renewal of formin-based filament elongation. As a result, the filament would appear to a treadmill, i.e., continue elongating at the barbed end while at the same time being disassembled at the pointed end by CAP-cofilin synergy. “B” denotes barbed end, “F” denotes formin, “C” denotes CP, and “T” denotes twinfilin.