INVOLVEMENT OF PROFILIN IN THE ACTIN-BASED MOTILITY OF L-MONOCYTOGENES IN CELLS AND IN CELL-FREE-EXTRACTS

Within hours of Listeria monocytogenes infection, host cell actin fila ments form a dense cloud around the intracytoplasmic bacteria and then rearrange to form a polarized comet tail that is associated with movi ng bacteria. We have devised a cell-free extract system capable of fai thfully reconstituting L. monocytogenes motility, and we have used thi s system to demonstrate that profilin, a host actin monomer-binding pr otein, is necessary for bacterial actin-based motility. We find that e xtracts from which profilin has been depleted do not support comet tai l formation or bacterial motility. In extracts and host cells, profili n is localized to the back half of the surface of motile L. monocytoge nes, the site of actin filament assembly in the tail. This association is not observed with L. monocytogenes mutants that do not express the ActA protein, a bacterial gene product necessary for motility and vir ulence. Profilin also fails to bind L. monocytogenes grown outside of host cytoplasm, suggesting that at least one other host cell factor is required for this association.