Cofilin dissociates Arp2/3 complex and branches from actin filaments.
BACKGROUND
Actin-based cellular motility requires spatially and temporally coordinated remodeling of a network of branched actin filaments. This study investigates how cofilin and Arp2/3 complex, two main players in the dendritic nucleation model, interact to produce sharp spatial transitions between densely branched filaments and long, unbranched filaments.


RESULTS
We found that cofilin binding reduces both the affinity of actin filaments for Arp2/3 complex and the stability of branches. We used fluorescence spectroscopy to measure the kinetics of cofilin association with filaments and the resulting dissociation of Arp2/3 complex and TIRF microscopy to visualize filament severing and the loss of actin filament branches. Cofilin severs filaments optimally when few actin subunits are occupied but dissociates branches rapidly only at higher occupancies. Effective debranching is nevertheless achieved, as a result of cooperative binding and reduced affinity of Arp2/3 complex for the filament, at cofilin concentrations below those required for direct competition.


CONCLUSIONS
Cofilin rapidly dissociates Arp2/3 complex and branches by direct competition for binding sites on the actin filament and by propagation of structural changes in the actin filament that reduce affinity for Arp2/3 complex.
Department of Molecular Cellular, Yale University, PO Box 208103, New Haven, CT 06520-8103, USA.
Chikio
C
Chan
Christopher C
CC
Beltzner
Thomas D
TD
Pollard
D051339:Actin Depolymerizing Factors / Q000235:genetics / Q000378:metabolism*; D051376:Actin-Related Protein 2-3 Complex / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure; D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D002465:Cell Movement / Q000502:physiology; D002645:Chickens; D011485:Protein Binding; D012568:Schizosaccharomyces / Q000166:cytology / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*
D051339:Actin Depolymerizing Factors; D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D029702:Schizosaccharomyces pombe Proteins; D000244:Adenosine Diphosphate