Motility of ActA protein-coated microspheres driven by actin polymerization

Actin polymerization is required for the generation of motile force at the leading edge of both lamellipodia and filopodia and also at the surface of motile intracellular bacterial pathogens such as Listeria monocytogenes. Local catalysis of actin filament polymerization is accomplished in L. monocytogenes by the bacterial protein ActA. Polystyrene beads coated with purified ActA protein can undergo directional movement in an actin-rich cytoplasmic extract. Thus, the actin polymerization-based motility generated by ActA can be used to move nonbiological cargo, as has been demonstrated for classical motor molecules such as kinesin and myosin. Initiation of unidirectional movement of a symmetrically coated particle is a function of bead size and surface protein density. Small beads (