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J. Biol. Chem., Vol. 282, Issue 11, 8435-8445, March 16, 2007

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How ATP Hydrolysis Controls Filament Assembly from Profilin-Actin

IMPLICATION FOR FORMIN PROCESSIVITY^*

Stéphane Romero¹, Dominique Didry, Eric Larquet, Nicolas Boisset, Dominique Pantaloni, and Marie-France Carlier²

From the Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette, and the Institut de Minéralogie et de Physique de la Matière Condensée, Université Pierre et Marie Curie, 75252 Paris, France

Formins catalyze rapid filament growth from profilin-actin, by remaining processively bound to the elongating barbed end. The sequence of elementary reactions that describe filament assembly from profilin-actin at either free or formin-bound barbed ends is not fully understood. Specifically, the identity of the transitory complexes between profilin and actin terminal subunits is not known; and whether ATP hydrolysis is directly or indirectly coupled to profilin-actin assembly is not clear. We have analyzed the effect of profilin on actin assembly at free and FH1-FH2-bound barbed ends in the presence of ADP and non-hydrolyzable CrATP. Profilin blocked filament growth by capping the barbed ends in ADP and CrATP/ADP-P_i states, with a higher affinity when formin is bound. We confirm that, in contrast, profilin accelerates depolymerization of ADP-F-actin, more efficiently when FH1-FH2 is bound to barbed ends. To reconcile these data with effective barbed end assembly from profilin-MgATP-actin, the nature of nucleotide bound to both terminal and subterminal subunits must be considered. All data are accounted for quantitatively by a model in which a barbed end whose two terminal subunits consist of profilin-ATP-actin cannot grow until ATP has been hydrolyzed and P_i released from the penultimate subunit, thus promoting the release of profilin and allowing further elongation. Formin does not change the activity of profilin but simply uses it for its processive walk at barbed ends. Finally, if profilin release from actin is prevented by a chemical cross-link, formin processivity is abolished.

Received for publication, October 20, 2006 , and in revised form, January 3, 2007.

^* This work was supported in part by European Commission for NoE "3D-EM" contract LSHG-CT-2004-502828 and Region Ile-de-France for convention SESAME 2000 E1435 supporting the JEOL 2100F installed at Institut de Minéralogie et de Physique de la Matière Condensée, UMR 7590 CNRS-UPMC. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1-S4.

¹ Supported by a fellowship from the Ligue Nationale contre le Cancer.

² Supported in part by the Ligue Nationale contre le Cancer (équipe labelisée) and by Human Frontiers in Science Program (HFSP) Research Grant RGP0072/2003-C. To whom correspondence should be addressed. Tel.: 33-1-69-82-34-65; Fax: 33-1-69-82-34-78; E-mail: carlier{at}lebs.cnrs-gif.fr.

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