Phospholipases A of Legionella pneumophila: Virulence Factors by Diversity?

Abstract

Legionella pneumophila possesses several virulence mediating factors; for example, it has two protein export systems: the type II (Lsp) and the type IVB (Dot/Icm) secretion systems. Both systems transport effector molecules, including lipolytic proteins such as phospholipases. L. pneumophila possesses two major phospholipase activities, phospholipase A (PLA) and lysophospholipase A (LPLA), both capable of hydrolyzing phospholipids and generating the reaction products: free fatty acids (PLA and LPLA), cytotoxic lysophospholipids (via the action of PLA), and water-soluble phosphodiesters, like glycerophosphorylcholine (via the subsequent action of LPLA on lysophospholipids). Patatins are a group of plant storage glycoproteins that show lipid acyl hydrolase activity. One of the corresponding proteins, PatA, was found to be an LPLA when expressed in Escherichia coli. The patA to patK genes of L. pneumophila have been determined to be expressed during bacterial growth in laboratory media. Furthermore, by the construction of knockout mutants, it was shown that patA contributes to secreted bacterial PLA and LPLA activities and is essential for intracellular replication of L. pneumophila, during both amoeba and macrophage infection, which implies an important role for lipolytic enzymes with respect to the pathogenic behavior of the bacterium. The high number of lipolytic enzymes present in L. pneumophila implies that lipids may be an important source of nutrients for the bacterium, and/or lipid hydrolysis is an essential step in bacterial establishment, especially within the host cell.