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Changes in myosin S1 orientation and force induced by a temperature increase
Peter J Griffiths1, Maria A Bagni, Barbara Colombini
1Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze, Viale G.B. Morgagni 63, I-50132 Florence, Italy. pjg@physiol.ox.ac.uk
Summary
Increased muscle temperature enhances myosin force generation by altering myosin subfragment 1 (S1) tail domain orientation. This structural change, observed via X-ray diffraction, suggests the tail domain plays a significant role in muscle force production.
Area of Science:
- Muscle physiology
- Biophysics
- Structural biology
Background:
- Myosin-based motility relies on myosin subfragment 1 (S1) angular displacement relative to actin.
- Elevated temperatures increase S1 force, suggesting altered S1 tail domain dynamics.
Purpose of the Study:
- To investigate the structural basis for temperature-induced force increase in myosin S1.
- To define the orientation of S1 relative to the myofilament axis using time-resolved X-ray diffraction.
Main Methods:
- Time-resolved X-ray diffraction was employed to measure M3 meridional reflection intensity.
- Sinusoidal length oscillations were used to probe structural changes during force generation.
- Intensity changes were analyzed at varying temperatures (4 to 22°C).
Main Results:
- M3 intensity changes showed sinusoidal patterns at low temperatures, becoming distorted at higher temperatures.
- A double intensity peak emerged at maximum shortening with increasing temperature.
- Simulations indicated a mean tail displacement of 0.73 nm toward the perpendicular.
Conclusions:
- Findings support a model where myosin S1 tail domain rotation contributes to force generation.
- Increased temperature shifts S1 tail orientation towards a more perpendicular projection.
- At least 62% of crossbridge compliance is attributed to the myosin S1 tail domain.