Fig. 5
From: Dissecting myosin-5B mechanosensitivity and calcium regulation at the single molecule level
The ratio of forward to backward steps determines myosin-5B run length and velocity under resistive load. a Force dependence of the average step size. Box plot in Supplementary Fig. 1c. b Step size distributions at ±1.2 pN (left panel) and ±2.4 pN (right panel). For resistive forces close to the stall force (+2.4 pN), the distributions of forward (>0) and backward (<0) steps become nearly symmetric. c Force dependence of the average forward (black squares) and backward (cyan squares) step size. d Force dependence of the ratio of forward to backward steps. The dotted cyan line is the fit of the exponential model equation \(R = R_0^ + {\mathrm{exp}}\left( { - \frac{{F \cdot d_{\rm{fwd/bwd}}^ + }}{{{{k}}_{\mathrm{B}} \cdot {{T}}}}} \right)\) to data for positive forces below the stall force, which gives R0+ = 54 ± 8 and dfwd/bwd+ = 8.2 ± 0.6 nm. e Force dependence of forward (black squares) and backward (cyan squares) stepping rates. Exponential fits \(k_{f,b} = k_{0f,b}^ \pm {\mathrm{exp}}\left( {\frac{{{{F}} \cdot {{d}}_{f,b}^ \pm }}{{{{k}}_{\mathrm{B}} \cdot {{T}}}}} \right)\) of forward (f) and backward (b) stepping rates for positive (+) and negative (−) forces gave: \(k_{0f}^ +\) = 6.5 ± 0.6 s−1, \(d_f^ +\) = 2.2 ± 0.3 nm; \(k_{0b}^ +\) = 10 ± 2 s−1, \(d_b^ +\) = 2.0 ± 0.4 nm. \(k_{0f}^ -\) = 14.6 ± 0.8 s−1, \({\mathrm{d}}_f^ -\) = 0.05 ± 0.15 nm; \(k_{0b}^ -\) = 54.1 ± 17.5 s−1; \(d_b^ -\) = 2.4 ± 0.9 nm. Error bars, s.e.m., nfwd = 2729, nbwd = 689. [ATP] = 100 μM. Red squares and dotted lines in a–c and e are, respectively, the unloaded step size and stepping rate measured with the single molecule motility assay at [ATP] = 100 μM (n = 42)
