Abstract
Myosins are motor proteins in cells. They move along actin by changing shape after making stereospecific interactions with the actin subunits1. As these are arranged helically, a succession of steps will follow a helical path. However, if the myosin heads are long enough to span the actin helical repeat (∼36 nm), linear motion is possible. Muscle myosin (myosin II) heads are about 16 nm long2, which is insufficient to span the repeat3. Myosin V, however, has heads of about 31 nm that could span 36 nm (refs 4, 5) and thus allow single two-headed molecules to transport cargo by walking straight5. Here we use electron microscopy to show that while working, myosin V spans the helical repeat. The heads are mostly 13 actin subunits apart, with values of 11 or 15 also found. Typically the structure is polar and one head is curved, the other straighter. Single particle processing reveals the polarity of the underlying actin filament, showing that the curved head is the leading one. The shape of the leading head may correspond to the beginning of the working stroke of the motor. We also observe molecules attached by one head in this conformation.
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Acknowledgements
We thank C. Veigel, H. White and S. Schmitz for discussions and E. Harvey for technical assistance supported by BBSRC (to J.T. and P.J.K.) and NIH (to J.T. and H. White).
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Walker, M., Burgess, S., Sellers, J. et al. Two-headed binding of a processive myosin to F-actin. Nature 405, 804–807 (2000). https://doi.org/10.1038/35015592
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DOI: https://doi.org/10.1038/35015592
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