Three-color single molecule imaging shows WASP detachment from Arp2/3 complex triggers actin filament branch formation

Three-color single molecule imaging shows WASP detachment from Arp2/3 complex triggers actin filament branch formation

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During cell locomotion and endocytosis, membrane-tethered WASP proteins stimulate actin filament nucleation by the Arp2/3 complex.This process generates highly branched arrays of filaments that grow toward the membrane to which they are tethered, a conflict that seemingly would restrict filament growth.Using three-color single-molecule imaging in vitro we revealed pentair hose how the dynamic associations of Arp2/3 complex with mother filament and WASP are temporally coordinated with initiation of daughter filament growth.We found that WASP proteins dissociated from filament-bound Arp2/3 complex prior to new filament growth.Further, mutations that accelerated release of WASP from filament-bound Arp2/3 complex proportionally accelerated branch formation.

These data suggest that while WASP here promotes formation of pre-nucleation complexes, filament growth cannot occur until it is triggered by WASP release.This provides a mechanism by which membrane-bound WASP proteins can stimulate network growth without restraining it.