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The Arp2/3 complex branches filament barbed ends: functional antagonism with capping proteins

Abstract

The Arp2/3 complex is an essential regulator of actin polymerization in response to signalling and generates a dendritic array of filaments in lamellipodia. Here we show that the activated Arp2/3 complex interacts with the barbed ends of filaments to initiate barbed-end branching. Barbed-end branching by Arp2/3 quantitatively accounts for polymerization kinetics and for the length correlation of the branches of filaments observed by electron microscopy. Filament branching is visualized at the surface of Listeria in a reconstituted motility assay. The functional antagonism between the Arp2/3 complex and capping proteins is essential in the maintenance of the steady state of actin assembly and actin-based motility.

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Figure 1: WA-activated Arp2/3 stimulates actin polymerization in an autocatalytic manner.
Figure 2: WA-activated Arp2/3 stimulates actin polymerization by interacting with barbed filament ends.
Figure 3: Branched filaments in solutions of actin polymerizing in the presence of WA-activated Arp2/3.
Figure 4: Evidence of barbed-end branching in bacterial actin-based motility.
Figure 5: Functional antagonism between capping proteins and Arp2/3 regulates the critical concentration.
Figure 6: Model for barbed-end branching of actin filaments by WA-activated Arp2/3.

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Acknowledgements

This work was funded in part by the Association pour la Recherche contre le Cancer (ARC), the Association Française contre les Myopathies (AFM) and the Ligue Nationale Française contre le Cancer, and by a grant from the Human Frontier in Science programme organization.

Correspondence and requests for materials should be addressed to M-F.C.

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Correspondence to Marie-France Carlier.

Supplementary information

Movie 1

Evidence of barbed-end branching in bacterial actin-based motility. (MOV 106 kb)

pActin-based motility of Listeria was observed in reconstituted motility medium modified by replacement of capping protein with gelsolin at a gelsolin/actin ratio of 1:500 (8 mM F-actin, 16 µM gelsolin). This time-lapse recording shows branched actin filaments continuing to grow immediately behind the bacterium at a 70° angle to the actin-tail axis.

Movie 2 (MOV 4247 kb)

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Pantaloni, D., Boujemaa, R., Didry, D. et al. The Arp2/3 complex branches filament barbed ends: functional antagonism with capping proteins. Nat Cell Biol 2, 385–391 (2000). https://doi.org/10.1038/35017011

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