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Molecular architecture of axonemal microtubule doublets revealed by cryo-electron tomography

Nature volume 442, pages 475478 (27 July 2006) | Download Citation

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Abstract

The axoneme, which forms the core of eukaryotic flagella and cilia, is one of the largest macromolecular machines, with a structure that is largely conserved from protists to mammals1. Microtubule doublets are structural components of axonemes that contain a number of proteins besides tubulin, and are usually found in arrays of nine doublets arranged around two singlet microtubules. Coordinated sliding of adjacent doublets, which involves a host of other proteins in the axoneme, produces periodic beating movements of the axoneme. We have obtained a three-dimensional density map of intact microtubule doublets using cryo-electron tomography and image averaging. Our map, with a resolution of about 3 nm, provides insights into locations of particular proteins within the doublets and the structural features of the doublets that define their mechanical properties. We identify likely candidates for several of these non-tubulin components of the doublets. This work offers insight on how tubulin protofilaments and accessory proteins attach together to form the doublets and provides a structural basis for understanding doublet function in axonemes.

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Acknowledgements

We thank A. Killilea for sea urchin collection, K. Gull for discussions on protofilament numbering, H. Li, B. Rockel and D. Typke for discussions and help with image processing, B. Heymann and C. Yang for discussions and help with BSOFT library usage, and R. Glaeser and M. Auer for suggestions and encouragement. This work is supported by NIH grants and by the US Department of Energy.

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  1. Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Haixin Sui
    •  & Kenneth H. Downing

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Corresponding author

Correspondence to Kenneth H. Downing.

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    Supplementary Notes

    This file contains Supplementary Figures 1–3, Supplementary Methods and additional references.

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https://doi.org/10.1038/nature04816

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