title: Calcium regulates scallop muscle by changing myosin flexibility.
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.
authors.affiliation: Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, NW7 1AA, London, UK.
authors.forename: Vian
authors.initials: V
authors.lastname: Azzu
authors.forename: David
authors.initials: D
authors.lastname: Yadin
authors.forename: Hitesh
authors.initials: H
authors.lastname: Patel
authors.forename: Franca
authors.initials: F
authors.lastname: Fraternali
authors.forename: Peter D
authors.initials: PD
authors.lastname: Chantler
authors.forename: Justin E
authors.initials: JE
authors.lastname: Molloy
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000648:ultrastructure; D000818:Animals; D002118:Calcium / Q000737:chemistry; D002413:Cations, Divalent; D003432:Cross-Linking Reagents / Q000737:chemistry; D005453:Fluorescence; D008958:Models, Molecular; D009038:Motion; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000502:physiology; D015879:Myosin Subfragments / Q000737:chemistry; D009218:Myosins / Q000737:chemistry* / Q000648:ultrastructure; D049897:Pectinidae / Q000737:chemistry* / Q000502:physiology
chemical_list: D000199:Actins; D002413:Cations, Divalent; D003432:Cross-Linking Reagents; D015879:Myosin Subfragments; D009218:Myosins; D002118:Calcium