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

Nature Structural & Molecular Biology volume 12, pages 26–31 (2005)Cite this article

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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Figure 1: Three different conformations of wild-type Arp2/3 complex.
Figure 2: Activated (WASp-bound) Arp2/3 complex is in the closed conformation and inactive (coronin-bound) Arp2/3 complex is in the open conformation.
Figure 3: Bovine Arp2/3 complex is suppressed for spontaneous activity and is skewed toward the open conformation.
Figure 4: Actin nucleation activities of mutant and wild-type Arp2/3 complexes.
Figure 5: Conformational states of the Arp2/3 complex.

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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.

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Author notes

  1. Avital A Rodal and Olga Sokolova: These authors contributed equally to this work.

Authors and Affiliations

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

    Olga Sokolova & Nikolaus Grigorieff

  3. Department of Cell Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland

    Simon Hippenmeyer

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

    Howard Riezman

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Correspondence to Bruce L Goode.

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Supplementary information

Supplementary Fig. 1

Difference maps between WASp-bound and open, intermediate, and closed structures. (PDF 182 kb)

Supplementary Fig. 2

Location of mutations in Arc35-5 and Arc35-6. (PDF 812 kb)

Supplementary Fig. 3

Response of Arc35-6 to WASp activation. (PDF 406 kb)

Supplementary Fig. 4

Arp2/3 preparations contain no contaminating WASp. (PDF 191 kb)

Supplementary Fig. 5

Electron micrograph of a field of Arp2/3 complexes. (PDF 1021 kb)

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Rodal, A., Sokolova, O., Robins, D. et al. Conformational changes in the Arp2/3 complex leading to actin nucleation. Nat Struct Mol Biol 12, 26–31 (2005). https://doi.org/10.1038/nsmb870

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