A Rickettsia WASP-like protein activates the Arp2/3 complex and mediates actin-based motility

Area of Science:

• Microbiology
• Cell Biology
• Pathogen-Host Interactions

Background:

• Spotted fever group Rickettsia are intracellular bacteria that manipulate host cell actin for movement and spread.
• Unlike other pathogens like Listeria monocytogenes, Rickettsia form unbranched actin tails through an unknown mechanism.

Purpose of the Study:

• To investigate the mechanism by which Rickettsia generate actin tails for motility.
• To identify the specific bacterial factors involved in Rickettsia actin-based motility.

Main Methods:

• Gene identification and characterization of Rickettsia proteins with similarity to WASP family activators (RickA).
• In vitro assays using purified RickA to assess Arp2/3 complex activation and actin nucleation.
• Microscopic bead motility assays in cell extracts to observe actin tail formation.

Main Results:

• Identified RickA proteins in Rickettsia species, homologous to WASP family Arp2/3 complex activators.
• Rickettsia rickettsii RickA activated the Arp2/3 complex, promoting actin nucleation and Y-branched filament formation, similar to other WASP proteins.
• RickA-coated beads exhibited motility in cell extracts, generating Y-branched actin tails.

Conclusions:

• Rickettsia utilize an Arp2/3 complex-dependent actin nucleation mechanism for motility, similar to other bacterial pathogens.
• The observed Y-branched actin networks likely undergo reorganization by additional Rickettsia or host factors into unbranched arrays for efficient cell-to-cell spread.