Identification of a bacterial factor required for actin-based motility ofBurkholderia pseudomallei.

Burkholderia pseudomalleiis a Gram-negative facultative intracellular pathogen that enters and escapes from eukaryotic cells using the power of actin polymerization. We have identified a bacterial protein (BimA) that is required for the ability ofB. pseudomalleito induce the formation of actin tails. BimA contains proline-rich motifs and WH2-like domains and shares limited homology at the C-terminus with theYersiniaautosecreted adhesin YadA. BimA is located at the pole of the bacterial cell at which actin polymerization occurs and mutation ofbimAabolished actin-based motility of the pathogen in J774.2 cells. Transient expression of BimA in HeLa cells resulted in F-actin clustering reminiscent of that seen on WASP overexpression. Antibody-mediated clustering of a CD32 chimera in which the cytoplasmic domain was replaced with BimA resulted in localization of the chimera to the tips of F-actin enriched membrane protrusions. We report that purified truncated BimA protein binds monomeric actin in a concentration-dependent manner in cosedimentation assays and that BimA stimulates actin polymerizationin vitroin a manner independent of the cellular Arp2/3 complex. [ABSTRACT FROM AUTHOR]