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    Mini-thin filaments regulated by troponin-tropomyosin

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    Authors
    Gong, Huiyu
    Hatch, Victoria
    Ali, Laith
    Lehman, William
    Craig, Roger W.
    Tobacman, Larry S.
    UMass Chan Affiliations
    Department of Cell Biology
    Document Type
    Journal Article
    Publication Date
    2005-01-13
    Keywords
    Actins
    Allosteric Regulation
    Animals
    Ca(2+) Mg(2+)-ATPase
    Calcium
    Cattle
    Gelsolin
    Macromolecular Substances
    Microfilaments
    Microscopy, Electron
    Muscle, Skeletal
    Myosin Subfragments
    Particle Size
    Protein Binding
    Tropomyosin
    Troponin
    Cell Biology
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    Link to Full Text
    http://dx.doi.org/10.1073/pnas.0407225102
    Abstract
    Striated muscle thin filaments contain hundreds of actin monomers and scores of troponins and tropomyosins. To study the cooperative mechanism of thin filaments, "mini-thin filaments" were generated by isolating particles nearly matching the minimal structural repeat of thin filaments: a double helix of actin subunits with each strand approximately seven actins long and spanned by a troponin-tropomyosin complex. One end of the particles was capped by a gelsolin (segment 1-3)-TnT fusion protein (substituting for normal TnT), and the other end was capped by tropomodulin. EM showed that the particles were 46 +/- 9 nm long, with a knob-like mass attributable to gelsolin at one end. Average actin, tropomyosin, and gelsolin-troponin composition indicated one troponin-tropomyosin attached to each strand of the two-stranded actin filament. The minifilaments thus nearly represent single regulatory units of thin filaments. The myosin S1 MgATPase rate stimulated by the minifilaments was Ca2+-sensitive, indicating that single regulatory length particles are sufficient for regulation. Ca2+ bound cooperatively to cardiac TnC in conventional thin filaments but noncooperatively to cardiac TnC in minifilaments in the absence of myosin. This suggests that thin filament Ca2+-binding cooperativity reflects indirect troponin-troponin interactions along the long axis of conventional filaments, which do not occur in minifilaments. Despite noncooperative Ca2+ binding to minifilaments in the absence of myosin, Ca2+ cooperatively activated the myosin S1-particle ATPase rate. Two-stranded single regulatory units therefore may be sufficient for myosin-mediated Ca2+-binding cooperativity. Functional mini-thin filaments are well suited for biochemical and structural analysis of thin-filament regulation.
    Source
    Proc Natl Acad Sci U S A. 2005 Jan 18;102(3):656-61. Epub 2005 Jan 11. Link to article on publisher's site
    DOI
    10.1073/pnas.0407225102
    Permanent Link to this Item
    http://hdl.handle.net/20.500.14038/27665
    PubMed ID
    15644437
    Related Resources
    Link to Article in PubMed
    ae974a485f413a2113503eed53cd6c53
    10.1073/pnas.0407225102
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