Fig. P1.
Stepping dynamics of full-length myosin Va (FL-myoV) and a constitutively active heavy meromyosin Va (HMM-myoV). (A) The average velocity (Vavg) and the velocity for periods of fast processive movement (Vfast) versus ionic strength for two FL-myoV splice variants (circles and squares), and Vavg for HMM-myoV (triangles). The FL-myoV Vavg was slower than the Vavg of HMM-myoV at all KCl concentrations (p ≤ 0.05). (B)–(C) Representative displacement vs. time traces for dual-labeled HMM-myoV (B) and the brain splice variant, FLB-myoV (C) at 100 mM KCl. (B) HMM-myoV exhibits almost exclusively hand-over-hand stepping. (C) FLB-myoV has a mixture of hand-over-hand (60%) and altered gating (33%) steps where the motor took ≥2 steps before the heads switched roles (highlighted by dashed box). FLB-myoV also took occasional backsteps, identified by an arrow. (D) Distributions of interhead distances for the HMM-myoV (red bars; Gaussian fit: 34 ± 2 nm) and the FLB-myoV (gray bars).