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© The Rockefeller University Press, 0021-9525/1997//1307 $5.00
The Journal of Cell Biology, Volume 136, Number 6, , 1997 1307-1322

Article

Actin Depolymerizing Factor (ADF/Cofilin) Enhances the Rate of Filament Turnover: Implication in Actin-based Motility



Marie-France Carlier*, Valérie Laurent*, Jérôme Santolini*, Ronald Melki*, Dominique Didry*, Gui-Xian Xia{ddagger}, Yan Hong{ddagger}, Nam-Hai Chua§, and Dominique Pantaloni*

* Dynamique du Cytosquelette, Laboratoire d'Enzymologie et Biochimie Structurales, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette Cedex, France; {ddagger} Laboratory of Plant Cell Biology, Institute of Molecular Agrobiology, National University of Singapore, Singapore 118240; and § Laboratory of Plant Molecular Biology, Rockefeller University, New York 10021

Actin-binding proteins of the actin depolymerizing factor (ADF)/cofilin family are thought to control actin-based motile processes. ADF1 from Arabidopsis thaliana appears to be a good model that is functionally similar to other members of the family. The function of ADF in actin dynamics has been examined using a combination of physical–chemical methods and actin-based motility assays, under physiological ionic conditions and at pH 7.8. ADF binds the ADPbound forms of G- or F-actin with an affinity two orders of magnitude higher than the ATP- or ADP-Pi– bound forms. A major property of ADF is its ability to enhance the in vitro turnover rate (treadmilling) of actin filaments to a value comparable to that observed in vivo in motile lamellipodia. ADF increases the rate of propulsion of Listeria monocytogenes in highly diluted, ADF-limited platelet extracts and shortens the actin tails. These effects are mediated by the participation of ADF in actin filament assembly, which results in a change in the kinetic parameters at the two ends of the actin filament. The kinetic effects of ADF are end specific and cannot be accounted for by filament severing. The main functionally relevant effect is a 25-fold increase in the rate of actin dissociation from the pointed ends, while the rate of dissociation from the barbed ends is unchanged. This large increase in the rate-limiting step of the monomer-polymer cycle at steady state is responsible for the increase in the rate of actin-based motile processes. In conclusion, the function of ADF is not to sequester G-actin. ADF uses ATP hydrolysis in actin assembly to enhance filament dynamics.

Abbreviations used in this paper: ADF, actin depolymerizing factor; NBD, 7-chloro-4-nitrobenzeno-2-oxa-1,3-diazole; Tβ4, thymosin β4.

This work was funded in part by the Association pour la Recherche contre le Cancer (ARC), the Association Française contre les Myopathies (AFM), the EC (grant No. CHRX-CT94-0652), the Ligue Nationale Française contre le Cancer, and a grant from the National Science and Technology Board, Singapore.

Address all correspondence to M.-F. Carlier, LEBS, CNRS, Gif-surYvette 91198, France. Tel.: 33-1-69 82 34 65. Fax: 33-1-69 82 31 29. E-mail: carlier{at}lebs.cnrs-gif.fr


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