Cooperativity of myosin II motors in the non-regulated and regulated thin filaments investigated with high-speed AFM
Bibliographic record
Abstract
Abstract Skeletal myosins II are non-processive molecular motors, that work in ensembles to produce muscle contraction while binding to the actin filament. Although the molecular properties of myosin II are well known, there is still debate about the collective work of the motors: is there cooperativity between myosin motors while binding to the actin filaments? In this study, we used high-speed AFM to evaluate this issue. We observed that the initial binding of small arrays of myosin heads to the non-regulated actin filaments did not affect the cooperative probability of subsequent bindings to neighboring sites and did not lead to an increase in the fractional occupancy of the actin binding sites. These results suggest that myosin motors are independent force generators when connected in small arrays, and that the binding of one myosin does not alter the kinetics of other myosins. In contrast, the probability of binding of myosin heads to regulated thin filaments under activating conditions (at high Ca 2+ concentration and with 2 μM ATP) was increased with the initial binding of one myosin, leading to a larger occupancy of neighboring available binding sites. The result suggests that myosin cooperativity is defined by the activation status of the thin filaments. eLife digest Muscle contraction is the result of large ensembles of the molecular motor myosin II working in coordination while attached to actin. Myosin II produces the power stroke, responsible for force generation. In this paper, we used High-Speed Atomic Force Microscopy (HS-AFM) to determine the potential cooperativity between myosin motors bound to non-regulated and regulated thin filaments. Based on the direct visualization of myosin-actin interaction, probability of myosin binding, and the myosin fractional occupancy of binding sites along non-regulated and regulated actin filaments, our results show no cooperative effects over ∼100 nm of the actin filament length. In contrast, there is myosin cooperativity within the activated thin filament, that induces a high affinity of myosin heads to the filaments. Our results support the independent behaviour of myosin heads while attached to actin filaments, but a cooperative behavior when attached to regulated thin filaments.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".