Legionella pneumophila Effector LpdA Is a Palmitoylated Phospholipase D Virulence Factor

Area of Science:

• Microbiology
• Cell Biology
• Biochemistry

Background:

• Legionella pneumophila causes severe pneumonia by hijacking host cells.
• Its Dot/Icm type IV secretion system (T4SS) delivers over 300 effectors.
• These effectors manipulate host cell signaling and membrane trafficking to create a replication niche.

Purpose of the Study:

• To characterize the LpdA effector, a phospholipase D involved in Legionella-containing vacuole (LCV) biogenesis.
• To investigate LpdA's subcellular localization, substrate specificity, and function in host cells.
• To determine LpdA's role in L. pneumophila virulence during infection.

Main Methods:

• Expressing LpdA in HeLa cells to determine subcellular localization and targeting motifs.
• Performing in vitro substrate specificity assays for LpdA.
• Analyzing the impact of LpdA on host cell membranes, including phosphatidylinositol phosphate (PIP) association and Golgi integrity.
• Assessing the replication of an L. pneumophila ΔlpdA mutant in a murine lung infection model.

Main Results:

• Ectopically expressed LpdA localized to the plasma membrane and Rab4/Rab14 vesicles, dependent on a S-palmitoylated C-terminal motif.
• LpdA hydrolyzed phosphatidylinositol phosphates and phosphatidylglycerol to phosphatidic acid (PA) in vitro and in cells.
• LpdA expression led to PA generation at cellular membranes and Golgi fragmentation, without affecting PIP probe association.
• An L. pneumophila ΔlpdA mutant showed reduced replication in murine lungs.

Conclusions:

• LpdA is a Legionella T4SS effector that modifies host cell membranes by generating phosphatidic acid.
• LpdA contributes to L. pneumophila virulence in vivo, likely through its effects on membrane trafficking and organelle structure.
• Targeting host lipid metabolism is a key strategy for L. pneumophila pathogenesis.