title: Structural dynamics of troponin during activation of skeletal muscle.
abstract: Time-resolved changes in the conformation of troponin in the thin filaments of skeletal muscle were followed during activation in situ by photolysis of caged calcium using bifunctional fluorescent probes in the regulatory and the coiled-coil (IT arm) domains of troponin. Three sequential steps in the activation mechanism were identified. The fastest step (1,100 s(-1)) matches the rate of Ca(2+) binding to the regulatory domain but also dominates the motion of the IT arm. The second step (120 s(-1)) coincides with the azimuthal motion of tropomyosin around the thin filament. The third step (15 s(-1)) was shown by three independent approaches to track myosin head binding to the thin filament, but is absent in the regulatory head. The results lead to a four-state structural kinetic model that describes the molecular mechanism of muscle activation in the thin filament-myosin head complex under physiological conditions.
authors.affiliation: Randall Division of Cell and Molecular Biophysics, King's College London, London SE1 1UL, United Kingdom.
authors.forename: Luca
authors.initials: L
authors.lastname: Fusi
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Brunello
authors.forename: Ivanka R
authors.initials: IR
authors.lastname: Sevrieva
authors.forename: Yin-Biao
authors.initials: YB
authors.lastname: Sun
authors.forename: Malcolm
authors.initials: M
authors.lastname: Irving
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D005456:Fluorescent Dyes; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D019209:Troponin C / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005456:Fluorescent Dyes; D019209:Troponin C; D002118:Calcium
keywords: excitation–contraction coupling; muscle regulation; muscle signaling