Journal Article

The AtMAP65-1 Cross-Bridge Between Microtubules is Formed by One Dimer

Hua Li, Tonglin Mao, Ziding Zhang and Ming Yuan

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 48, issue 6, pages 866-874
Published in print June 2007 | ISSN: 0032-0781
Published online June 2007 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcm059
The AtMAP65-1 Cross-Bridge Between Microtubules is Formed by One Dimer

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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 antiparallel overlapping dimer instead of an end-to-end dimer. We then tested this model by using truncations of AtMAP65-1. EDC {[3-(dimethylamino) propyl] carbodiimide} 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 participates in connecting the two antiparallel 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 with 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: Arabidopsis thaliana; AtMAP65-1; Bundles; Cross-bridge; Microtubules

Journal Article.  4623 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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