Fraction of colocalized cofilin clusters leading to two-filament bundle fragmentation. Related to Fig. 5. At 100 nM cofilin, a fraction of colocalized cluster regions on two-filament bundles that have not yet led to the fragmentation of the bundle, versus time (n = 36 events). The dashed line shows the best fit by a computed curve (with k_init,2 = 8 × k_init,SF, see Materials and methods), using a chi-square minimization procedure, yielding a cofilin cluster severing rate k_sev,2 = 2.7 × 10⁻³ s⁻¹ (±0.8, SD), close to the one observed on single filaments (see Fig. S10).