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Myosin VI Walks “Wiggly” on Actin Filaments

Yujie Sun, John F. Beausang, W. Harry (Trey) Schroeder III, Yale E. Goldman (University of Pennsylvania)

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Myosin VI is a puzzle because it moves “backwards” (towards the pointed or (-) end) on the actin filament and because it is too small to span its 30-36 nm stride. We measured the tilting motions of calmodulin bound to the single exchangeable binding (IQ) site and found chaotic and surprisingly large azimuthal motions.

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The ß (axial angle) value for the leading head (larger angle peak in the pink histogram above) has a wider distribution than ß for the trailing head. This may indicate the lever arm is uncoupled, or that the searching range of actin monomers is large. The a angles (green) are distributed over their allowable scope. The ‘wiggly’ motion of myosin VI enables it to hit actin monomers 4, 6, 7, 9, 11 and 15, accounting for its known variable step size. The broad range of angles and steps is likely to indicate an unfolded portion of the proximal tail domain.

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