The manifold phospholipases A of Legionella pneumophila – Identification, export, regulation, and their link to bacterial virulence

The intracellular lung pathogen Legionella pneumophila expresses secreted and cell-associated phospholipase A (PLA) and lysophospholipase A (LPLA) activities belonging to at least three enzyme families. The first family consists of three secreted PLA and LPLA activities displaying the amino acid signature motif ‘GDSL’; PlaA, PlaC and PlaD. The second group contains the cell-associated and very potent PLA/LPLA, PlaB. The third group, the patatin-like proteins, comprises 11 members. One patatin-like protein, PatA/VipD, shows LPLA and PLA activities and interferes with vesicular trafficking when expressed in yeast and therefore is possibly involved in the intracellular infection process. Likewise, members of the first two phospholipase families have roles in bacterial virulence because phospholipases are important virulence factors that have been shown to promote bacterial survival, spread and host cell modification/damage. The GDSL enzyme PlaA detoxifies cytolytic lysophospholipids, and PlaB shows contact-dependent haemolytic activity. PlaC acylates cholesterol, a lipid present in eukaryotic hosts but not in the bacterium. Many of the L. pneumophila PLAs are exported by the type II Lsp or the type IVB Dot/Icm secretion systems involved in virulence factor export. Moreover, the regulation of lipolytic activities depends on the transcriptional regulators LetA/S and RpoS, inducing the expression of virulence traits, and on posttranscriptional activators like the zinc metalloprotease ProA.