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Plant and Cell Physiology Advance Access originally published online on May 15, 2007
Plant and Cell Physiology 2007 48(6):886-891; doi:10.1093/pcp/pcm054
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© The Author 2007. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Short Communication

Enzymatic Activity and Motility of Recombinant Arabidopsis Myosin XI, MYA1

You Hachikubo1, Kohji Ito1, John Schiefelbein2, Dietmar J. Manstein3 and Keiichi Yamamoto1,*

1Department of Biology, Chiba University, Inageku, Chiba, 263-8522 Japan
2Department of Molecular, Cellular, and Developmental Biology, University of Michigan, MI, USA
3Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany

*Corresponding author: E-mail, yamamoto{at}bio.s.chiba-u.ac.jp; Fax, +81-43-290-2809.


  Abstract

We expressed recombinant Arabidopsis myosin XI (MYA1), in which the motor domain of MYA1 was connected to an artificial lever arm composed of triple helical repeats of Dictyostelium {alpha}-actinin, in order to understand its motor activity and intracellular function. The Vmax and Kactin of the actin-activated Mg2+ ATPase activity of the recombinant MYA1 were 50.7 Pi head–1 s–1 and 30.2 µM, respectively, at 25°C. The recombinant MYA1 could translocate actin filament at the maximum velocity of 1.8 µm s–1 at 25°C in the in vitro motility assay. The value corresponded to a motility of 3.2 µm s–1 for native MYA1 if we consider the difference in the lever arm length, and this value was very close to the velocity of cytoplasmic streaming in Arabidopsis hypocotyl epidermal cells. The extent of inhibition by ADP of the motility of MYA1 was similar to that of the well-known processive motor, myosin V, suggesting that MYA1 is a processive motor. The dissociation rate of the actin–MYA1-ADP complex induced by ATP (73.5 s–1) and the Vmax value of the actin-activated Mg2+ ATPase activity revealed that MYA1 stays in the actin-bound state for about 70% of its mechanochemical cycle time. This high ratio of actin-bound states is also a characteristic of processive motors. Our results strongly suggest that MYA1 is a processive motor and involved in vesicle transport and/or cytoplasmic streaming.

Keywords: Arabidopsis - ATPase - Motility - MYA1 - Myosin - Processivity

Abbreviations: BSA, bovine serum albumin; DTT, dithiothreitol; eYFP, enhanced yellow fluorescent protein; 2ME, 2-mercaptoethanol.

(Received March 27, 2007; Accepted May 6, 2007)
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