Nature Structural & Molecular Biology
12, 26 - 31 (2004)
Published online: 12 December 2004; | doi:10.1038/nsmb870
Conformational changes in the Arp2/3 complex leading to actin nucleationAvital A Rodal1, 5, Olga Sokolova2, 5, Deborah B Robins1, Karen M Daugherty1, Simon Hippenmeyer3, Howard Riezman4, Nikolaus Grigorieff2
& Bruce L Goode11
Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts, 02454, USA. 2
Howard Hughes Medical Institute and Department of Biochemistry, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts, 02454, USA. 3
Biozentrum, Department of Cell Biology, University of Basel, Klingelbergstrasse 70, CH-4056
Basel, Switzerland.
4
Department of Biochemistry, University of Geneva, Sciences II, 30 Quai E. Ansermet, CH-1211
Geneva, Switzerland. 5
These authors contributed equally to this work.
Correspondence should be addressed to Bruce L Goode goode@brandeis.edu.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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