Decoupling the coupling: surface attachment in actin-based motility.

Actin filament polymerization provides the driving force for several kinds of actin-based motility, propelling loads such as the plasma membrane at the leading edge of a crawling cell, an endosomal vesicle, or an intracellular bacterial pathogen. In these systems, branched filament networks continuously grow while simultaneously remaining attached to the load. Previous experiments have suggested an important role in both actin filament nucleation and filament attachment for a family of proteins called nucleation-promoting factors (NPFs) that stimulate actin branch formation and nucleation by the Arp2/3 complex. A recent report demonstrates that N-WASP, an NPF, uses distinct domains to mediate nucleation and attachment during motility. The surprising details of the biochemical mechanism necessitate reconsideration of the biophysical models proposed for actin-based motility.