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  • The EMBO Journal (2003) 22, 1263 - 1272
  • doi:10.1093/emboj/cdg130

Higher plant myosin XI moves processively on actin with 35 nm steps at high velocity

Motoki Tominaga1, Hiroaki Kojima1, Etsuo Yokota2, Hidefumi Orii2, Rinna Nakamori1, Eisaku Katayama3,4, Michael Anson5, Teruo Shimmen2 and Kazuhiro Oiwa1

  1. Kansai Advanced Research Center, Communications Research Laboratory, Kobe 651-2492, Japan
  2. Department of Life Science, Graduate School and Faculty of Science, Himeji Institute of Technology, Harima Science Park City, Hyogo 678-1297, Japan
  3. Division of Biomolecular Imaging, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo 108-8639, Japan
  4. PRESTO, Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012 Japan
  5. Division of Physical Biochemistry, National Institute for Medical Research, Mill Hill, London NW7 1AA, UK

Correspondence to:

Kazuhiro Oiwa, E-mail: oiwa@crl.go.jp

Received 17 October 2002; Accepted 27 January 2003; Revised 21 January 2003

High velocity cytoplasmic streaming is found in various plant cells from algae to angiosperms. We characterized mechanical and enzymatic properties of a higher plant myosin purified from tobacco bright yellow-2 cells, responsible for cytoplasmic streaming, having a 175 kDa heavy chain and calmodulin light chains. Sequence analysis shows it to be a class XI myosin and a dimer with six IQ motifs in the light chain-binding domains of each heavy chain. Electron microscopy confirmed these predictions. We measured its ATPase characteristics, in vitro motility and, using optical trap nanometry, forces and movement developed by individual myosin XI molecules. Single myosin XI molecules move processively along actin with 35 nm steps at 7 mum/s, the fastest known processive motion. Processivity was confirmed by actin landing rate assays. Mean maximal force was approx0.5 pN, smaller than for myosin IIs. Dwell time analysis of beads carrying single myosin XI molecules fitted the ATPase kinetics, with ADP release being rate limiting. These results indicate that myosin XI is highly specialized for generation of fast processive movement with concomitantly low forces.

  • Keywords:

    • in vitro motility,
    • myosin XI,
    • optical trap,
    • processivity,
    • single molecule