The Structural Basis of Myosin V Processive Movement as Revealed by Electron Cryomicroscopy

Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, United States
Molecular Cell (Impact Factor: 14.02). 10/2005; 19(5):595-605. DOI: 10.1016/j.molcel.2005.07.015
Source: PubMed


The processive motor myosin V has a relatively high affinity for actin in the presence of ATP and, thus, offers the unique opportunity to visualize some of the weaker, hitherto inaccessible, actin bound states of the ATPase cycle. Here, electron cryomicroscopy together with computer-based docking of crystal structures into three-dimensional (3D) reconstructions provide the atomic models of myosin V in both weak and strong actin bound states. One structure shows that ATP binding opens the long cleft dividing the actin binding region of the motor domain, thus destroying the strong binding actomyosin interface while rearranging loop 2 as a tether. Nucleotide analogs showed a second new state in which the lever arm points upward, in a prepower-stroke configuration (lever arm up) bound to actin before phosphate release. Our findings reveal how the structural elements of myosin V work together to allow myosin V to step along actin for multiple ATPase cycles without dissociating.

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    • "They found a tight one-to-one coupling of nucleotide utilization for each step in the single molecule fluorescence assay and found that the leading head had little tendency to release nucleotide as long as the trail head was attached. This is consistent with load dependence effectively gating the kinetics of the two heads to aid in the processive movement, as has been suggested in the earlier single molecule mechanical experiments (Veigel et al., 2001). "
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    • "Evidence suggests that the answer may be that strong binding to actin stiffens the head. 3-D reconstructions of actin filaments saturated with myosin heads from various sources [32] [46] [47] [48] consistently show strong features in the levers, and a lack of contact between them, out to high radius from the actin, implying that the lever maintains a rather fixed geometric relationship to the actin helix, i.e. it is not flexing at the MD-lever junction. NMR studies of myosin heads found over 20% of mobile structure and all this became immobile upon binding actin [49]. "
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