Biophys. J. The Phospholipid Sphingolipid People
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Biophysical Journal 86:3804-3810 (2004)
© 2004 The Biophysical Society

Unconstrained Steps of Myosin VI Appear Longest among Known Molecular Motors

M. Yusuf Ali * {dagger}, Kazuaki Homma {ddagger}, Atsuko Hikikoshi Iwane §, Kengo Adachi *, Hiroyasu Itoh ¶ ||, Kazuhiko Kinosita, Jr. *, Toshio Yanagida § and Mitsuo Ikebe {ddagger}

* Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Higashiyama 5-1, Myodaiji, Okazaki 444-8787, Japan; {dagger} Department of Physics, Faculty of Physical Sciences, Shahjalal University of Science and Technology, Sylhet-3114, Bangladesh; {ddagger} Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655-0127, USA; § Department of Physiology and Biosignaling, Graduate School of Medicine, Osaka University, Yamadaoka 2-2, Suita 565-0871, Japan; Tsukuba Research Laboratory, Hamamatsu Photonics KK, Tokodai, Tsukuba 300-2635, Japan; and || Core Research for Evolutional Science and Technology "Creation and Application of Soft Nano-Machine, the Hyperfunctional Molecular Machine" Team 13*, Tokodai, Tsukuba 300-2635, Japan

Correspondence: Address reprint requests to Kazuhiko Kinosita Jr., Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Higashiyama 5-1, Myodaiji, Okazaki 444-8787, Japan. Tel.: 81-564-59-5230; Fax: 81-59-564-5234; E-mail: kazuhiko@ims.ac.jp.

Myosin VI is a two-headed molecular motor that moves along an actin filament in the direction opposite to most other myosins. Previously, a single myosin VI molecule has been shown to proceed with steps that are large compared to its neck size: either it walks by somehow extending its neck or one head slides along actin for a long distance before the other head lands. To inquire into these and other possible mechanism of motility, we suspended an actin filament between two plastic beads, and let a single myosin VI molecule carrying a bead duplex move along the actin. This configuration, unlike previous studies, allows unconstrained rotation of myosin VI around the right-handed double helix of actin. Myosin VI moved almost straight or as a right-handed spiral with a pitch of several micrometers, indicating that the molecule walks with strides slightly longer than the actin helical repeat of 36 nm. The large steps without much rotation suggest kinesin-type walking with extended and flexible necks, but how to move forward with flexible necks, even under a backward load, is not clear. As an answer, we propose that a conformational change in the lifted head would facilitate landing on a forward, rather than backward, site. This mechanism may underlie stepping of all two-headed molecular motors including kinesin and myosin V.






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Copyright © 2004 by the Biophysical Society.