Fig. 2
Sliding on immobilized myosin 1b increases F-actin depolymerization. a Representative kymographs of stabilized F-actin (top) or polymerizing F-actin with 0.6 µM G-actin (bottom), on uncoated glass or sliding on glass coated with Myo1b (2 mM and 0.2 mM ATP (see Supplementary Movies 2 and 3) or MyoII (see Supplementary Movie 6). The sliding distance ΔX and the elongation ΔL of the filaments are indicated by white arrows. Actin fluorescence intensity is represented according to the Fire LUT of Image J. Scale bar, 5μm. 1 image/10 s. b Dot plot representation of the sliding velocities vf of stabilized (top) and polymerizing actin filaments (0.6 µM G-actin) (bottom) on immobilized Myo1b (8000 molecules/μm2) at 2 mM (blue) or 0.2 mM (gray) ATP or sliding on MyoII at 2 mM ATP (orange). The number of analyzed filaments and the mean-values ± s.e.m. are indicated. c Filament elongation ΔL (normalized by the length of the actin subunit (su) equal to 2.7 nm) versus time for filaments shown in A (bottom) in the absence of myosins and in the presence of MyoII or Myo1b at two ATP concentrations. The polymerization rate at the barbed end vp (in su/s) is deduced from the slope. d vp as a function of G-actin concentration Cm for the different conditions. The fits correspond to \(v_p = k_{on}C_m - k_{off}\), with kon the rate of association of G-actin and koff the rate of dissociation. \(C_{c + }\) is the critical concentration for polymerization. Inset: koff for the different conditions. Error bars represent s.e.m. (n > 25). Source data are provided as a Source Data file. e Model for the role of Myo1b motor on the dissociation (depolymerization) rate koff. The filament, sliding at velocity vf, experiences a force Fmot at the barbed end while the motor is attached, thus impacting koff, but not the association (polymerization) rate kon
