title: Interaction sites of tropomyosin in muscle thin filament as identified by site-directed spin-labeling.
abstract: To identify interaction sites we measured the rotational motion of a spin label covalently bound to the side chain of a cysteine genetically incorporated into rabbit skeletal muscle tropomyosin (Tm) at positions 13, 36, 146, 160, 174, 190, 209, 230, 271, and 279. Upon the addition of F-actin, the mobility of all the spin labels, especially at position 13, 271, or 279, of Tm was inhibited significantly. Slow spin-label motion at the C-terminus (at the 230th and 271st residues) was observed upon addition of troponin. The binding of myosin-head S1 fragments without troponin immobilized Tm residues at 146, 160, 190, 209, 230, 271, and 279, suggesting that these residues are involved in a direct interaction between Tm and actin in its open state. As immobilization occurred at substoichiometric amounts of S1 binding to actin (a 1:7 molar ratio), the structural changes induced by S1 binding to one actin subunit must have propagated and influenced interaction sites over seven actin subunits.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Ueda
authors.forename: Chieko
authors.initials: C
authors.lastname: Kimura-Sakiyama
authors.forename: Tomoki
authors.initials: T
authors.lastname: Aihara
authors.forename: Masao
authors.initials: M
authors.lastname: Miki
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Arata
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D000818:Animals; D003497:Cyclic N-Oxides / Q000737:chemistry / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D008698:Mesylates / Q000737:chemistry / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits; D012399:Rotation; D013113:Spin Labels; D013997:Time Factors; D014335:Tropomyosin / Q000378:metabolism*; D014336:Troponin / Q000378:metabolism
chemical_list: D000199:Actins; D003497:Cyclic N-Oxides; D004220:Disulfides; D008698:Mesylates; D013113:Spin Labels; D014335:Tropomyosin; D014336:Troponin; C017480:4-maleimido-2,2,6,6-tetramethylpiperidinooxyl; C074502:methanethiosulfonate