The Kinetics of Mechanically Coupled Myosins Exhibit Group Size-Dependent Regimes

Abstract

Naturally occurring groups of muscle myosin behave differently from individual myosins or small groups commonly assayed in vitro. Here, we investigate the emergence of myosin group behavior with increasing myosin group size. Assuming the number of myosin binding sites (N) is proportional to actin length (L) (N = L/35.5 nm), we resolve in vitro motility of actin propelled by skeletal muscle myosin for L = 0.2-3 μm. Three distinct regimes were found: L < 0.3 μm, sliding arrest; 0.3 μm ≤ L ≤ 1 μm, alternation between arrest and continuous sliding; L > 1 μm, continuous sliding. We theoretically investigated the myosin group kinetics with mechanical coupling via actin. We find rapid actin sliding steps driven by power-stroke cascades supported by postpower-stroke myosins, and phases without actin sliding caused by prepower-stroke myosin buildup. The three regimes are explained: N = 8, rare cascades; N = 15, cascade bursts; N = 35, continuous cascading. Two saddle-node bifurcations occur for increasing N (mono → bi → mono-stability), with steady states corresponding to arrest and continuous cascading. The experimentally measured dependence of actin sliding statistics on L and myosin concentration is correctly predicted.

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

“…Outside the cellular context, properties of the main isoforms of myosin II motors (skeletal muscle, smooth muscle, non-muscle A and B) can be studied in motility assays [8][9][10] and actomyosin gels [11][12][13][14][15]. In the latter case, one often works with myosin II minifilaments from skeletal or smooth muscle, because they are easier to prepare and to control than those from non-muscle myosin II.…”

Phosphate and ADP Differently Inhibit Coordinated Smooth Muscle Myosin Groups

“…4 C). Our recent model for skeletal muscle myosin showed that Post myosins are required for a rapid progression of Pre myosins through the main power stroke (8). We hypothesized that, similarly, a stabilization of smooth muscle myosins in the Post state should lead to a more persistent stepping from the Pre to the Post state, and thus more persistent mechanochemical activity.…”

“…We simulated myosin group kinetics by adapting our recently developed mathematical model of the in vitro propulsion of actin filaments (8) to include the effect of P i and ADP on individual smooth muscle myosin kinetics (Fig. 4).…”

“…In a recent in vitro motility study of skeletal muscle myosin groups of~5-50 motors, we used our newly developed analysis software to detect formerly unknown qualitative regimes in the coordinated mechanochemistry of myosin groups (7,8). These regimes depended on myosin group size ( Fig.…”

Simultaneous nano-tracking of multiple motor proteins via spectral discrimination of quantum dots

“…We believe that this measurement scheme would be useful for understanding the cooperativity of multiple motor proteins working in close proximity. While the current study only employed isolated molecules of processive linear motors for demonstration, the developed microscopy is also applicable to other subjects involving linear motor proteins, including cooperative transport of a single cargo by multiple linear motors [43][44][45] and cooperativity among multiple myosin-II heads on a thick filament of muscle [46,47]. Aside from linear motor proteins, measurement of multiple proteins in a rotatory motor system [31,32] and molecular complexes of membrane proteins [20,33] could also be potential applications.…”