The AtMAP65-1 cross-bridge between microtubules is formed by one dimer |
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Authors: | Li Hua Mao Tonglin Zhang Ziding Yuan Ming |
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Institution: | State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100094, PR China. |
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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 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. |
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Keywords: | Arabidopsis thaliana - AtMAP65-1 - Bundles - Cross-bridge - Microtubules |
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