Major project results are: Size exclusion chromatography and cross-linking with paraformaldehyde shows that Strep-PlaB forms homodimers. - Analytical ultracentrifugation shows that Strep-PlaB forms homodimers and homotetramers. - SAXS analysis confirms formation of PlaB tetramers and shows that the C-terminal 15 amino acids are not essential for oligomerization. - Monomeric but not tetrameric PlaB represents active phospholipase A. - The entire C-terminal 15 amino acid region of PlaB is essential for lipolytic and hemolytic activities but not for oligomerization. - Alanine mutagenesis showed that every polar amino acid within the 15 C-terminal amino acids is important for enzyme activity. - PlaB catalytic activity contributes to efficient intracellular replication of L. pneumophila in RAW 264.7 mouse macrophages. - PlaB is most prominently found during stationary growth phase PlaB is located in the bacterial outer membrane and faces outside of bacterium. - PlaB is not exported to the bacterial surface by the known L. pneumophila secretion systems. - N- and C-terminal regions of PlaB contribute to the efficiency of surface presentation.