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| Subject Categories:
Cell & Tissue Architecture
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The EMBO Journal
(2006) 25, 1184–1195, doi:10.1038/sj.emboj.7601019 Published online 2 March 2006
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| Mammalian twinfilin sequesters ADP-G-actin and caps filament barbed ends: implications in motility |
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Emmanuèle Helfer1, 3, Elisa M Nevalainen2, 3, Perttu Naumanen2, Stéphane Romero1, Dominique Didry1, Dominique Pantaloni1, Pekka Lappalainen2 and Marie-France Carlier1
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1 Cytoskeleton Dynamics and Motility, LEBS, CNRS, Gif-sur-Yvette, France
2 Institute of Biotechnology, University of Helsinki, Finland
To whom correspondence should be addressed
Marie-France Carlier, Dynamique du Cytosquelette, LEBS, CNRS, Gif-sur-Yvette F-91198, France. Tel.: +33 1 69 82 34 65; Fax: +33 1 69 82 341 29; E-mail: carlier@lebs.cnrs-gif.fr Pekka Lappalainen, Institute of Biotechnology, University of Helsinki, Finland. Tel.: +358 9 191 59499; E-mail: Pelappal@operoni.helsinki.fi
3 These authors equally contributed to the work
Received 30 June 2005; Accepted 2 February 2006; Published online 2 March 2006.
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| Abstract |
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| Twinfilins are conserved actin-binding proteins composed of two actin depolymerizing factor homology (ADF-H) domains. Twinfilins are involved in diverse morphological and motile processes, but their mechanism of action has not been elucidated. Here, we show that mammalian twinfilin both sequesters ADP-G-actin and caps filament barbed ends with preferential affinity for ADP-bound ends. Twinfilin replaces capping protein and promotes motility of N-WASP functionalized beads in a biomimetic motility assay, indicating that the capping activity supports twinfilin's function in motility. Consistently, in vivo twinfilin localizes to actin tails of propelling endosomes. The ADP-actin-sequestering activity cooperates with the filament capping activity of twinfilin to finely regulate motility due to processive filament assembly catalyzed by formin-functionalized beads. The isolated ADF-H domains do not cap barbed ends nor promote motility, but sequester ADP-actin, the C-terminal domain showing the highest affinity. A structural model for binding of twinfilin to barbed ends is proposed based on the similar foldings of twinfilin ADF-H domains and gelsolin segments. |
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| Keywords: actin, ADF homology domains, capping proteins, motility, twinfilin |
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