Fig. 1

Assessing the number of HMMs available for actin interaction from rigor rupture events. a Schematics of the protocol: (1) formation of rigor bonds between the HMM array (blue) by the optical fibre (grey) and the actin filament (red) attached to the trapped bead (dark grey) via gelsolin (yellow); (2) optical fibre moved away from the actin filament in the direction (z) orthogonal to the actin–myosin interface. b Records of the nanopositioner movement (black, ΔZ velocity 25 nm s⁻¹) and force with different [HMM] (colours refer to different concentrations as indicated in c; green: 25 µg ml⁻¹; violet: 38 µg ml⁻¹; red: 50 µg ml⁻¹; blue: 100 µg ml⁻¹). The small vertical bars indicate the rupture events (force drop <2.5 pN, complete in <50 ms and not rapidly reversed), the last of which corresponds to complete detachment of the actin filament. c Relation between the number of ruptures per interaction and [HMM] (mean ± SD, n = 14)