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    Myosin Va becomes a low duty ratio motor in the inhibited form

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    Authors
    Sato, Osamu
    Li, Xiang-Dong
    Ikebe, Mitsuo
    UMass Chan Affiliations
    Department of Physiology
    Document Type
    Journal Article
    Publication Date
    2007-03-17
    Keywords
    Actins
    Adenosine Diphosphate
    Adenosine Triphosphate
    Animals
    Calcium
    Egtazic Acid
    Enzyme Activation
    Humans
    Hydrolysis
    Kinetics
    Mice
    Myosin Heavy Chains
    Myosin Type V
    Protein Binding
    *Protein Folding
    Recombinant Proteins
    Life Sciences
    Medicine and Health Sciences
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    Link to Full Text
    http://dx.doi.org/10.1074/jbc.M610766200
    Abstract
    Vertebrate myosin Va is a typical processive motor with high duty ratio. Recent studies have revealed that the actin-activated ATPase activity of the full-length myosin Va (M5aFull) is inhibited at a low [Ca(2+)], which is due to the formation of a folded conformation of M5aFull. To clarify the underlying inhibitory mechanism, we analyzed the actin-activated ATP hydrolysis mechanism of the M5aFull at the inhibited and the activated states, respectively. Marked differences were found in the hydrolysis, P(i) release, and ADP release steps between the activated and the inhibited states. The kinetic constants of these steps of the activated state were similar to those of the unregulated S1 construct, in which the rate-limiting step was the ADP release step. On the other hand, the P(i) release rate from acto-M5aFull was decreased in EGTA by >1,000-fold, which makes this step the rate-limiting step for the actin-activated ATP hydrolysis cycle of M5aFull. The ADP off rate from acto-M5aFull was decreased by approximately 10-fold, and the equilibrium between the prehydrolysis state and the post hydrolysis state was shifted toward the former state in the inhibited state of M5aFull. Because of these changes, M5aFull spends a majority of the ATP hydrolysis cycling time in the weak actin binding state. The present results indicate that M5aFull molecules at a low [Ca(2+)] is inhibited as a cargo transporter not only due to the decrease in the cross-bridge cycling rate but also due to the decrease in the duty ratio thus being dissociated from actin.
    Source
    J Biol Chem. 2007 May 4;282(18):13228-39. Epub 2007 Mar 14. Link to article on publisher's site
    DOI
    10.1074/jbc.M610766200
    Permanent Link to this Item
    http://hdl.handle.net/20.500.14038/38408
    PubMed ID
    17363376
    Related Resources
    Link to Article in PubMed
    ae974a485f413a2113503eed53cd6c53
    10.1074/jbc.M610766200
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