Complementary activities of SseJ and SifA regulate dynamics of the Salmonella typhimurium vacuolar membrane

Area of Science:

• Microbiology
• Cell Biology
• Infectious Diseases

Background:

• Salmonella typhimurium utilizes the Salmonella pathogenicity island 2 (SPI-2) type III secretion system (TTSS) to facilitate intracellular replication.
• The TTSS translocates effector proteins, such as SifA, which are essential for maintaining the Salmonella-containing vacuole (SCV) membrane integrity and forming Salmonella-induced filaments (Sifs).

Purpose of the Study:

• To investigate the roles of putative SPI-2 effector genes (sifB, srfJ, sseJ, sseI) in Salmonella typhimurium virulence.
• To elucidate the function of the SseJ effector protein in SCV dynamics and host cell interaction.

Main Methods:

• Generating and analyzing S. typhimurium mutant strains (sifB, srfJ, sseJ, sseI, sifA sseJ double mutant) for virulence defects in mice.
• Expressing SseJ in HeLa cells to observe its effect on vacuolar structures and Sif formation.
• Immunofluorescence microscopy to examine the localization of SseJ and its association with SCVs and Sifs.

Main Results:

• A mutation in sseJ caused mild attenuation of S. typhimurium systemic virulence in mice.
• Expression of SseJ in host cells induced globular membranous compartments (GMCs) and inhibited Sif formation.
• SseJ associated with Sifs and SCV membranes, and its activity was dependent on a predicted acyltransferase/lipase active site.
• The sifA sseJ double mutant, unlike the sifA mutant, retained its vacuolar membrane, indicating SseJ's role in SCV membrane breakdown.

Conclusions:

• SseJ is a novel SPI-2 effector that plays a significant role in Salmonella virulence and SCV membrane dynamics.
• The combined action of SseJ and SifA is critical for regulating the dynamics of the SCV membrane within infected host cells.