Fig. 4.

Myosin-5B velocity and run length and detachment rate from actin are force sensitive. Force dependence of myosin-5B average velocity (a), run length (b), and detachment rate (c). Detachment rate is calculated as k = 1/<τ>, where <τ> is the average run duration. In all panels, assistive forces are negative, resistive forces are positive. Red squares are the unloaded velocity (a), run length (b), and detachment rate (c) measured with the single-molecule motility assay (n = 30). Cyan curves in b and c are fits of the exponential model equations $L=L_0^{\pm }\exp \left(-\frac{F\cdot d_L^{\pm }}{k_{\mathrm{B}}\cdot T}\right)$ and $k=k_0^{\pm }\exp \left(\frac{F\cdot d_k^{\pm }}{k_{\mathrm{B}}\cdot T}\right)$to the data, where F is the absolute value of the force, k_B the Boltzmann constant, T the temperature, and + or − superscripts indicate free parameters under positive or negative force, respectively. Fitted parameters are L₀⁻ = 148 ± 12 nm, L₀⁺ = 890 ± 120 nm, d_L⁻ = 1.9 ± 0.3 nm, d_L⁺ = 6.3 ± 0.6 nm and k₀⁻ = 2.3 ± 0.4 s⁻¹, k₀⁺ = 0.64 ± 0.09 s⁻¹, d_k⁻ = 1.9 ± 0.5 nm, d_k⁺ = 4.2 ± 0.4 nm. Fisher f-test applied to run length and detachment rate data under positive and negative force gave p value = 2E−5 and 6E−3, respectively, indicating significant difference of myosin-5B mechanosensitivity with force direction. [ATP] = 100 µM. n = 756. Error bars (a, b), s.e.m. (c), s.e.m. obtained from error propagation σ_k = σ_τ < τ > ⁻². Box plots of run length and detachment rate box plot are shown as Supplementary Fig. 1a, b