Sensitivity of small myosin II ensembles from different isoforms to mechanical load and ATP concentration

Abstract

Based on a detailed crossbridge model for individual myosin II motors, we systematically study the influence of mechanical load and ATP concentration on small myosin II ensembles made from different isoforms. For skeletal and smooth muscle myosin II, which are often used in actomyosin gels that reconstitute cell contractility, fast forward movement is restricted to a small region of phase space with low mechanical load and high ATP concentration, which is also characterized by frequent ensemble detachment. At high load, these ensembles are stalled or move backwards, but forward motion can be restored by decreasing ATP concentration. In contrast, small ensembles of non-muscle myosin II isoforms, which are found in the cytoskeleton of non-muscle cells, are hardly affected by ATP concentration due to the slow kinetics of the bound states. For all isoforms, the thermodynamic efficiency of ensemble movement increases with decreasing ATP concentration, but this effect is weaker for the non-muscle myosin II isoforms.

Myosin II filament dynamics in actin networks revealed with interferometric scattering microscopy

“…The correlation between run length and dwell time is stronger than at 100 µM ATP with most myosin II filaments exhibiting persistent motion for up to 6 s (Pearson coefficient 0.57) and a loss of this correlation at longer dwell times (Pearson coefficient -0.18) ( Fig 3H). We emphasize that the myosin II filament motion is more persistent and faster at 10 µM ATP as compared to 100 µM ATP in agreement with recent theoretical studies (15,23). These results suggest that increased processivity and dwell time with decreasing ATP concentrations provides a molecular mechanism underlying the transition from a remodeling to a contractile acto-myosin network.…”

“…Our approach allowed us to determine that a change in myosin II filament dwell times from τ1,100µM ATP = 1.23 s to τ1,10µM ATP = 3.7 s switches the acto-myosin network from a remodeling to a contractile state, and that myosin II filaments move faster and more processively at 10 µM ATP. This effect of ATP concentration on myosin II filaments under load provides evidence for predictions made by theoretical studies (15,23). Our observations indicate that the control of myosin dwell times could provide an ideal way for a biological system to switch between a remodeling or fluid-like network state to a contractile or solid-like state.…”

“…short interactions on the order of τoff1 (1.23 s at 100 μM ATP and 3.7 s at 10 μM ATP) and the other with long interactions on the order of τoff2 (12.6 s at 100 μM ATP and 11.9 s at 10 μM ATP). Compared to the dwell time of a single myosin head domain of 25-40 ms, the observed dwell times are much longer and probably represent the concerted binding of multiple myosin head domains of the same filament (15,27). It remains to be elucidated what the nature of the two dwell time populations is.…”

“…Despite exhaustive experimental and theoretical analysis on the molecular and macroscopic level, the processes that lead from a remodeling, fluid-like acto-myosin network at high ATP concentrations to a contractile, solid-like network at low ATP concentrations remain poorly understood.Experimental approaches to studying myosin motor properties focuses largely on in vitro motility assays and optical tweezer studies, which have been used to probe the dynamics of single head domains. Recent advances in the theoretical understanding of myosin filament dynamics, which arise from multiple, interacting myosin head domains, indicate that small changes in the single head duty ratio in combination with the cooperative effects between the head domains can lead to a switch between nonprocessive and processive behavior of myosin II filaments (12)(13)(14)(15). Corresponding experimental studies, however, are still missing.…”

Polarity sorting drives remodeling of actin-myosin networks

“…properties and the formation of much smaller bipolar filament ensembles of only 10-20 motors 302 (Erdmann et al, 2016). Clearly, in future it will be interesting to study if end-dwelling is also observed for 303 non-muscle myosin.…”