Rickettsia Sca2 Recruits Two Actin Subunits for Nucleation but Lacks WH2 Domains

The Rickettsia ∼1,800 amino acid autotransporter protein Sca2 promotes actin polymerization on the surface of the bacterium to drive its movement using an actin comet tail mechanism. Sca2 mimics eukaryotic formins in that it promotes both actin filament nucleation and elongation and competes with capping protein to generate filaments that are long and unbranched. However, despite these functional similarities, Sca2 is structurally unrelated to eukaryotic formins and achieves these functions through an entirely different mechanism.

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