Sca2 Autotransporter

The C-terminal β-barrel domain inserts into the bacterial outer membrane, which anchors Sca2 while presenting its passenger domain on the surface. This arrangement places the actin-interacting region where it can contact the host cytoplasm after invasion. Its membrane anchoring and surface exposure therefore connect bacterial secretion with manipulation of the host cytoskeleton.

The exposed passenger domain acts in a formin-like manner, promoting the formation of polarized actin filaments. Polarization gives filament assembly a directional organization rather than producing an undirected network. That spatial control is central to generating the organized force needed for bacterial movement through the host-cell cytoplasm.

Polarized actin assembly produces an actin comet tail behind the intracellular bacterium. The tail provides a directional basis for propulsion, allowing the bacterium to move through the host cytoplasm instead of remaining localized. This mechanism links a specific cytoskeletal organization to both intracellular motility and the ability to reach neighboring cells.

Sca2 links two functional stages of infection: its C-terminal β-barrel supports surface display through a type V secretion system, while its passenger domain influences host actin. Surface presentation enables cytoskeletal interaction, and the resulting movement supports intracellular dissemination. This makes Sca2 a useful example of how secretion machinery can contribute directly to virulence.

A useful sequence is surface display, host-actin engagement, polarized filament assembly, comet-tail formation, intracellular propulsion, and cell-to-cell spread. Examining these linked events helps distinguish the structural role of the β-barrel from the cytoskeletal role of the passenger domain. It also connects molecular activity with the broader outcome of pathogen dissemination.

Sca2 provides a focused model for examining how a bacterial surface protein redirects host-cell actin to support infection. Its activity connects bacterial architecture, actin-filament organization, intracellular movement, and spread between cells. Studying this system can therefore clarify both bacterial motility and the mechanisms by which pathogens exploit host cytoskeletal processes.