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Plant and Cell Physiology Advance Access published online on May 15, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm059
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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 e-mail: journals.permissions@oxfordjournals.org

The AtMAP65-1 cross-bridge between microtubules is formed by one dimer

Hua Li1, Tonglin Mao1, Ziding Zhang and Ming Yuan*

State Key Laboratory of Plant Physiology and Biochemistry; Department of Plant Sciences, College of Biological Sciences, China Agricultural University, Beijing 100094, China

Corresponding author: Ming Yuan. Department of Plant Sciences, College of Biological Sciences, China Agricultural University, Beijing 100094, China. Telephone: 8610-62733436, FAX: 8610-62733491, E-mail: mingyuan{at}cau.edu.cn


  Abstract

The microtubule-associated protein, AtMAP65-1 from Arabidopsis thaliana dimerizes and forms 25-nm cross-bridges between microtubules but the exact mechanism is unknown. Here, we used the predicted three-dimensional structure of AtMAP65-1 as a basis for analyzing the actual cross-bridging in detail. Fold-recognition predicts that AtMAP65-1 contains four coiled-coil domains and a flexible extended loop. The length of these coiled-coil domains is about 25-nm, suggesting that one molecule could span the gap, hence forming an anti-parallel overlapping dimer instead of an end-to-end dimer. We then tested this model by using truncations of AtMAP65-1. EDC cross-linking analysis indicated that the N-terminus of the rod domain of AtMAP65-1 (amino acids 1-339) binds to the C-terminus of the rod domain (amino acids 340-494) and also participated in connecting the two anti-parallel proteins in the cross-bridge. Nevertheless, microtubules can still form bundles in the presence of AtMAP65-1 340-587 (amino acids 340-587) or AtMAP65-1 1-494 (amino acids 1-494). Comparing the cold stability of microtubule bundles induced by full length AtMAP65-1 against that of AtMAP65-1 340-587 or AtMAP65-1 1-494, we conclude that AtMAP65-1 495-587 acts as a flexible extended loop, playing a crucial role in binding to and stabilizing microtubules in the AtMAP65-1 cross-bridge.

Keywords: AtMAP65-1 - Arabidopsis thaliana - Bundles - Cross-bridge - Microtubules

1These authors have contributed equally to this paper and are considered joint first authors.


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[Abstract] [Full Text] [PDF]


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