Mechanism of Interaction of Acanthamoeba Actophorin (ADF/Cofilin) with Actin Filaments

We characterized the interaction ofAcanthamoeba actophorin, a member of ADF/cofilin family, with filaments of amoeba and rabbit skeletal muscle actin. The affinity is about 10 times higher for muscle actin filaments (Kd = 0.5 μm) than amoeba actin filaments (Kd = 5 μm) even though the affinity for m...

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Bibliographic Details
Published in:The Journal of biological chemistry 1999-05, Vol.274 (22), p.15538-15546
Main Authors: Blanchoin, Laurent, Pollard, Thomas D.
Format: Article
Language:English
Subjects:
Acanthamoeba
Acanthamoeba - metabolism
Actin Depolymerizing Factors
Actins - metabolism
Animals
Beryllium - pharmacology
Fluorescence Polarization
Fluorides - pharmacology
Kinetics
Microfilament Proteins - metabolism
Muscle, Skeletal - metabolism
Phosphates - metabolism
Protein Binding - drug effects
Protozoan Proteins - metabolism
Pyrenes
Rabbits
Rhodamines
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Summary:We characterized the interaction ofAcanthamoeba actophorin, a member of ADF/cofilin family, with filaments of amoeba and rabbit skeletal muscle actin. The affinity is about 10 times higher for muscle actin filaments (Kd = 0.5 μm) than amoeba actin filaments (Kd = 5 μm) even though the affinity for muscle and amoeba Mg-ADP-actin monomers (Kd = 0.1 μm) is the same (Blanchoin, L., and Pollard, T. D. (1998) J. Biol. Chem. 273, 25106–25111). Actophorin binds slowly (k+ = 0.03 μm−1 s−1) to and dissociates from amoeba actin filaments in a simple bimolecular reaction, but binding to muscle actin filaments is cooperative. Actophorin severs filaments in a concentration-dependent fashion. Phosphate or BeF3 bound to ADP-actin filaments inhibit actophorin binding. Actophorin increases the rate of phosphate release from actin filaments more than 10-fold. The time course of the interaction of actophorin with filaments measured by quenching of the fluorescence of pyrenyl-actin or fluorescence anisotropy of rhodamine-actophorin is complicated, because severing, depolymerization, and repolymerization follows binding. The 50-fold higher affinity of actophorin for Mg-ADP-actin monomers (Kd = 0.1 μm) than ADP-actin filaments provides the thermodynamic basis for driving disassembly of filaments that have hydrolyzed ATP and dissociated γ-phosphate.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.274.22.15538