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.