Calcium regulates scallop muscle by changing myosin flexibility |
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Authors: | Vian Azzu David Yadin Hitesh Patel Franca Fraternali Peter D Chantler Justin E Molloy |
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Institution: | (1) Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, NW7 1AA London, UK;(2) Unit of Molecular and Cellular Biology, Royal Veterinary College, Royal College Street, NW1 0TU London, UK |
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Abstract: | Muscle myosins are molecular motors that convert the chemical free energy available from ATP hydrolysis into mechanical displacement
of actin filaments, bringing about muscle contraction. Myosin cross-bridges exert force on actin filaments during a cycle
of attached and detached states that are coupled to each round of ATP hydrolysis. Contraction and ATPase activity of the striated
adductor muscle of scallop is controlled by calcium ion binding to myosin. This mechanism of the so-called “thick filament
regulation” is quite different to vertebrate striated muscle which is switched on and off via “thin filament regulation” whereby
calcium ions bind to regulatory proteins associated with the actin filaments. We have used an optically based single molecule
technique to measure the angular disposition adopted by the two myosin heads whilst bound to actin in the presence and absence
of calcium ions. This has allowed us to directly observe the movement of individual myosin heads in aqueous solution at room
temperature in real time. We address the issue of how scallop striated muscle myosin might be regulated by calcium and have
interpreted our results in terms of the structures of smooth muscle myosin that also exhibit thick filament regulation.
This paper is not being submitted elsewhere and the authors have no competing financial interests |
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