Study Reveals How ATP Concentration Controls Myosin-Driven Remodeling of Actin Networks
Researchers used reconstituted actomyosin networks and a technique called mean back relaxation (MBR) to quantify how ATP-driven myosin II activity pushes cytoskeletal networks out of thermal equilibrium. The study found that nonequilibrium activity peaks at intermediate ATP concentrations (0.2–0.5 mM) and declines at higher concentrations, suggesting a trade-off between network stiffening and active remodeling. These findings establish MBR as a sensitive tool for detecting active matter behavior in biological systems, with implications for understanding how cells regulate cytoskeletal mechanics.
Using purified components to build minimal actomyosin networks in vitro, researchers combined passive microrheology with mean back relaxation (MBR) analysis to isolate and quantify the nonequilibrium fluctuations driven by ATP-dependent myosin II activity. The study revealed that active, out-of-equilibrium behavior is strongest at intermediate ATP concentrations (0.2–0.5 mM) and diminishes at higher ATP levels, pointing to a fundamental trade-off between ATP-dependent network stiffening and myosin-driven structural remodeling. Although single-bead displacement distributions appeared roughly Gaussian, pooled data showed apparent heavy tails that were traced primarily to bead-to-bead heterogeneity rather than frequent large active bursts. MBR distinguished time-irreversible dynamics by separating passive restoring relaxation from persistent active motion, revealing nonequilibrium signatures that other methods missed. A minimal active Langevin simulation reproduced the MBR observations, supporting a model in which rare myosin-driven cage rearrangements are sufficient to generate detectable nonequilibrium behavior. The work provides a quantitative, bottom-up framework for studying how ATP concentration tunes cytoskeletal activity, which is difficult to isolate in living cells.
What's missing
The study is a preprint and has not yet undergone peer review. The reconstituted system uses purified components and lacks the full complexity of the cellular cytoskeleton, including regulatory proteins, membrane interactions, and spatial organization; how well these findings translate to in vivo conditions remains an open question. The mechanism by which higher ATP concentrations suppress nonequilibrium activity relative to the intermediate optimum is not fully explained.
What different sources said
- bioRxivCenter
Myosin activity drives entangled actin networks out-of-equilibrium - a quantitative approach
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