Pivotal role of VASP in Arp2/3 complex-mediated actin nucleation, actin branch-formation, and Listeria monocytogenes motility

The Listeria monocytogenes ActA protein mediates actin-based motility by re cruiting and stimulating the Arp2/3 complex. In vitro, the actin monomer-bi nding region of ActA is critical for stimulating Arp2/3-dependent actin nuc leation; however, this region is dispensable for actin-based motility in ce lls. Here, we provide genetic and biochemical evidence that vasodilator-sti mulated phosphoprotein (VASP) recruitment by ActA can bypass defects in act in monomer-binding. Furthermore, purified VASP enhances the actin-nucleatin g activity of wild-type ActA and the Arp2/3 complex while also reducing the frequency of actin branch formation. These data suggest that ActA stimulat es the Arp2/3 complex by both VASP-dependent and -independent mechanisms th at generate distinct populations of actin filaments in the comet tails of L . monocytogenes. The ability of VASP to contribute to actin filament nuclea tion and to regulate actin filament architecture highlights the central rol e of VASP in actin-based motility.