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Movement and force produced by a single myosin head
J E Molloy1, J E Burns, J Kendrick-Jones
1Department of Biology, University of York, UK.
Abstract:
Muscle contraction is driven by the cyclical interaction of myosin with actin, coupled to the breakdown of ATP. Studies of the interaction of filamentous myosin and of a double-headed proteolytic fragment, heavy meromyosin (HMM), with actin have demonstrated discrete mechanical events, arising from stochastic interaction of single myosin molecules with actin. Here we show, using an optical-tweezers transducer, that a single myosin subfragment-1 (S1), which is a single myosin head, can act as an independent generator of force and movement. Our analysis accounts for the broad distribution of displacement amplitudes observed, and indicates that the underlying movement (working stroke) produced by a single acto-S1 interaction is approximately 4 nm, considerably shorter than previous estimates but consistent with structural data. We measure the average force generated by S1 or HMM to be at least 1.7 pN under isometric conditions.
Insights
A single myosin head (S1) generates force and movement during muscle contraction. This study reveals the working stroke is approximately 4 nm, shorter than previously thought, with forces of at least 1.7 pN.
Area of Science:
- Muscle physiology
- Molecular motor mechanics
- Biophysics
Background:
- Muscle contraction relies on myosin-actin interactions and ATP hydrolysis.
- Previous studies used filamentous myosin and heavy meromyosin (HMM) to investigate these interactions.
- Discrete mechanical events were observed, attributed to stochastic single myosin molecule interactions.
Purpose of the Study:
- To determine if a single myosin subfragment-1 (S1), a single myosin head, can independently generate force and movement.
- To quantify the mechanical properties of single acto-S1 interactions.
- To reconcile observed displacement amplitudes with structural data.
Main Methods:
- Utilized an optical-tweezers transducer to measure the force and displacement generated by single myosin S1 molecules.
- Analyzed the stochastic interactions between single myosin S1 heads and actin filaments.
- Measured isometric force generation under controlled conditions.
Main Results:
- Demonstrated that a single myosin S1 head acts as an independent generator of force and movement.
- Quantified the underlying movement (working stroke) of a single acto-S1 interaction at approximately 4 nm.
- Measured an average force of at least 1.7 pN generated by S1 or HMM under isometric conditions.
Conclusions:
- Single myosin heads are capable of generating force and movement independently.
- The working stroke of a single myosin head is approximately 4 nm, aligning with structural data.
- This research provides new insights into the fundamental mechanics of muscle contraction at the single-molecule level.