title: Modulation of the effects of tropomyosin on actin and myosin conformational changes by troponin and Ca2+.
abstract: The molecular mechanisms by which troponin (TN)-tropomyosin (TM) regulates the myosin ATPase cycle were investigated using fluorescent probes specifically bound to Cys36 of TM, Cys707 of myosin subfragment-1, and Cys374 of actin incorporated into ghost muscle fibers. Intermediate states of actomyosin were simulated by using nucleotides and non-hydrolysable ATP analogs. Multistep changes in mobility and spatial arrangement of SH1 helix of myosin motor domain and actin subdomain-1 during the ATPase cycle were observed. Each intermediate state of actomyosin induced a definite conformational state and specific position of TM strands on the surface of thin filament. TM increased the amplitude of myosin SH1 helix and actin subdomain-1 movements at transition from weak- to strong-binding states shifting to the center of thin filament at strong-binding and to the periphery of thin filament at weak-binding states. TN modulated those movements in a capital ES, Cyrillicsmall a, Cyrillic(2+)-dependent manner. At high-Ca(2+), TN enhanced the effect of TM on SH1 helix and subdomain-1 movements by transferring TM further to the center of thin filament at strong-binding states. In contrast, at low-Ca(2+), TN inhibited the effect of TM movements, "freezing" actin structure in "OFF" state and TM in the position typical for weak-binding states, resulting in disturbing the interplay of actin and myosin.
authors.affiliation: Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, St. Petersburg 194064, Russia. boroviko@mail.cytspb.rsii.ru
authors.forename: Yurii S
authors.initials: YS
authors.lastname: Borovikov
authors.forename: Olga E
authors.initials: OE
authors.lastname: Karpicheva
authors.forename: Stanislava V
authors.initials: SV
authors.lastname: Avrova
authors.forename: Charles S
authors.initials: CS
authors.lastname: Redwood
mesh_terms: D000199:Actins / Q000737:chemistry*; D000818:Animals; D002118:Calcium / Q000737:chemistry*; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D009218:Myosins / Q000737:chemistry*; D011487:Protein Conformation; D011817:Rabbits; D014335:Tropomyosin / Q000737:chemistry*
chemical_list: D000199:Actins; D005456:Fluorescent Dyes; D014335:Tropomyosin; D009218:Myosins; D002118:Calcium