The structural basis of actin filament branching by the Arp2/3 complex.
The actin-related protein 2/3 (Arp2/3) complex mediates the formation of branched actin filaments at the leading edge of motile cells and in the comet tails moving certain intracellular pathogens. Crystal structures of the Arp2/3 complex are available, but the architecture of the junction formed by the Arp2/3 complex at the base of the branch was not known. In this study, we use electron tomography to reconstruct the branch junction with sufficient resolution to show how the Arp2/3 complex interacts with the mother filament. Our analysis reveals conformational changes in both the mother filament and Arp2/3 complex upon branch formation. The Arp2 and Arp3 subunits reorganize into a dimer, providing a short-pitch template for elongation of the daughter filament. Two subunits of the mother filament undergo conformational changes that increase stability of the branch. These data provide a rationale for why branch formation requires cooperative interactions among the Arp2/3 complex, nucleation-promoting factors, an actin monomer, and the mother filament.
Rouiller
Isabelle
I
Burnham Institute for Medical Research, La Jolla, CA 92037, USA.
Xu
Xiao-Ping
XP
Amann
Kurt J
KJ
Egile
Coumaran
C
Nickell
Stephan
S
Nicastro
Daniela
D
Li
Rong
R
Pollard
Thomas D
TD
Volkmann
Niels
N
Hanein
Dorit
D
D048248:Acanthamoeba castellanii; D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure*; D051376:Actin-Related Protein 2-3 Complex / Q000737:chemistry* / Q000648:ultrastructure*; D000818:Animals; D002417:Cattle; D003198:Computer Simulation; D003599:Cytoskeleton / Q000737:chemistry* / Q000648:ultrastructure*; D019281:Dimerization; D046911:Macromolecular Substances / Q000737:chemistry; D008958:Models, Molecular; D011485:Protein Binding / Q000502:physiology; D020836:Protein Structure, Quaternary / Q000502:physiology; D011817:Rabbits; D012441:Saccharomyces cerevisiae; D014057:Tomography, X-Ray Computed
D051376:Actin-Related Protein 2-3 Complex; D046911:Macromolecular Substances