Figure 5.

(a) Gallery of HMM heads attached to actin during sliding, but with different orientation from those in Figure 4a. Though the global configuration of the particles is the same as that of thiol-crosslinked one, the lever-arm portions are visible and the plane including upper and lower 50 KDa subdomains in these particles is oriented almost perpendicular to the main axis of actin-filament, similarly to that under rigor condition. Since actin contacts through two paired-sites are established in this orientation, simple extension of the lever-arm from this state might readily and smoothly lead to rigor-configuration (i.e., the power-stroke); (b) A particle in rigor configuration. (N.B.: Though the statistical analyses are still left as the matter for future study, tentative ratio of particles in “weakly-bound configuration” vs. “primed configuration” vs. “Vi configuration” among actin-bound myosin heads during sliding might be very roughly 6:3:1). Refer to [33] for further arguments. Scale bars exhibit 10 nm.