Kinetic analysis of the interaction of actin-depolymerizing factor (ADF)/cofilin with G- and F-actins. Comparison of plant and human ADFs and effect of phosphorylation.
The thermodynamics and kinetics of actin interaction with Arabidopsis thaliana actin-depolymerizing factor (ADF)1, human ADF, and S6D mutant ADF1 protein mimicking phosphorylated (inactive) ADF are examined comparatively. ADFs interact with ADP.G-actin in rapid equilibrium (k+ = 155 microM-1.s-1 and k- = 16 s-1 at 4 degreesC under physiological ionic conditions). The kinetics of interaction of plant and human ADFs with F-actin are slower and exhibit kinetic cooperativity, consistent with a scheme in which the initial binding of ADF to two adjacent subunits of the filament nucleates a structural change that propagates along the filament, allowing faster binding of ADF in a "zipper" mode. ADF binds in a non-cooperative faster process to gelsolin-capped filaments or to subtilisin-cleaved F-actin, which are structurally different from standard filaments (Orlova, A., Prochniewicz, E., and Egelman, E. H. (1995) J. Mol. Biol. 245, 598-607). In contrast, the binding of phalloidin to F-actin cooperatively inhibits its interaction with ADF. The ADF-facilitated nucleation of ADP.actin self-assembly indicates that ADF stabilizes lateral interactions in the filament. Plant and human ADFs cause only partial depolymerization of F-actin at pH 8, consistent with identical functions in enhancing F-actin dynamics. Phosphorylation does not affect ADF activity per se, but decreases its affinity for actin by 20-fold.
Dynamique du Cytosquelette, Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, 91198 Gif-sur-Yvette, France.
F
F
Ressad
D
D
Didry
G X
GX
Xia
Y
Y
Hong
N H
NH
Chua
D
D
Pantaloni
M F
MF
Carlier
D051339:Actin Depolymerizing Factors; D000199:Actins / Q000378:metabolism*; D000818:Animals; D017360:Arabidopsis / Q000378:metabolism*; D001704:Biopolymers; D006801:Humans; D007700:Kinetics; D008840:Microfilament Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011817:Rabbits; D013050:Spectrometry, Fluorescence
D051339:Actin Depolymerizing Factors; D000199:Actins; D001704:Biopolymers; D008840:Microfilament Proteins