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Conformational changes in the Arp2/3 complex leading to actin nucleation

Nature Structural & Molecular Biology volume 12, pages 2631 (2005) | Download Citation

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Abstract

The two actin-related subunits of the Arp2/3 complex, Arp2 and Arp3, are proposed to form a pseudo actin dimer that nucleates actin polymerization. However, in the crystal structure of the inactive complex, they are too far apart to form such a nucleus. Here, we show using EM that yeast and bovine Arp2/3 complexes exist in a distribution among open, intermediate and closed conformations. The crystal structure docks well into the open conformation. The activator WASp binds at the cleft between Arp2 and Arp3, and all WASp-bound complexes are closed. The inhibitor coronin binds near the p35 subunit, and all coronin-bound complexes are open. Activating and loss-of-function mutations in the p35 subunit skew conformational distribution in opposite directions, closed and open, respectively. We conclude that WASp stabilizes p35-dependent closure of the complex, holding Arp2 and Arp3 closer together to nucleate an actin filament.

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Acknowledgements

We are grateful to D. Sousa and M. Rigney for helping with image processing, and to H. Higgs for suggesting the bovine Arp2/3 complex experiments and generously providing those purified proteins. We thank H. Balcer, F. Chang, D. DeRosier, M. Eck and D. Pellman for scientific discussions and comments on the manuscript. H.R. was supported by the Swiss National Science Foundation. N.G. and B.G. were supported by the US National Institutes of Health. B.G. was also supported by a Pew Scholars Award and the American Cancer Society.

Author information

Author notes

    • Avital A Rodal
    •  & Olga Sokolova

    These authors contributed equally to this work.

Affiliations

  1. Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts, 02454, USA.

    • Avital A Rodal
    • , Deborah B Robins
    • , Karen M Daugherty
    •  & Bruce L Goode
  2. Howard Hughes Medical Institute and Department of Biochemistry, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts, 02454, USA.

    • Olga Sokolova
    •  & Nikolaus Grigorieff
  3. Biozentrum, Department of Cell Biology, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.

    • Simon Hippenmeyer
  4. Department of Biochemistry, University of Geneva, Sciences II, 30 Quai E. Ansermet, CH-1211 Geneva, Switzerland.

    • Howard Riezman

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The authors declare no competing financial interests.

Corresponding author

Correspondence to Bruce L Goode.

Supplementary information

PDF files

  1. 1.

    Supplementary Fig. 1

    Difference maps between WASp-bound and open, intermediate, and closed structures.

  2. 2.

    Supplementary Fig. 2

    Location of mutations in Arc35-5 and Arc35-6.

  3. 3.

    Supplementary Fig. 3

    Response of Arc35-6 to WASp activation.

  4. 4.

    Supplementary Fig. 4

    Arp2/3 preparations contain no contaminating WASp.

  5. 5.

    Supplementary Fig. 5

    Electron micrograph of a field of Arp2/3 complexes.

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DOI

https://doi.org/10.1038/nsmb870

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