Penn Medicine
   
 

Yale Goldman, M.D., Ph.D.

Sun, Y., Sato, O., Ruhnow, F., Arsenault, M.E., Ikebe, M. and Goldman, Y.E.

Single Molecule Stepping and Structural Dynamics of Myosin X.

Nat. Struct. and Mol. Biol. In Press, 2010

Myosin X is an unconventional myosin with puzzling motility properties. We studied the motility of myosin X using single molecule fluorescence techniques – polTIRF, FIONA, and Parallax to measure rotation angles and 3-dimensional (3D) position of the molecule during its walk. Myosin X monomers induced to dimerize by clustering on actin filaments or by adding a strong coiledcoil forming sequence from the myosin V tail are both processive. It was found that Myosin X
steps processively in a hand-over-hand manner following a left-handed helical path along both single actin filaments and bundles made with fascin. Its step size and velocity are smaller on actin bundles than individual filaments, suggesting myosin X often steps onto neighboring filaments in a bundle. The data suggest that a previously postulated single a-helical domain mechanically extends the 3-IQ motif lever arm and either the neck-tail hinge or the tail is flexible. These structural features, in conjunction with the membrane and microtubule binding domains, enable myosin X to perform multiple functions on varied actin structures in cells.

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