title: Phospholipase PlaB of Legionella pneumophila represents a novel lipase family: protein residues essential for lipolytic activity, substrate specificity, and hemolysis.
abstract: Legionella pneumophila possesses several phospholipases capable of host cell manipulation and lung damage. Recently, we discovered that the major cell-associated hemolytic phospholipase A (PlaB) shares no homology to described phospholipases and is dispensable for intracellular replication in vitro. Nevertheless, here we show that PlaB is the major lipolytic activity in L. pneumophila cell infections and that PlaB utilizes a typical catalytic triad of Ser-Asp-His for effective hydrolysis of phospholipid substrates. Crucial residues were found to be located within the N-terminal half of the protein, and amino acids embedding these active sites were unique for PlaB and homologs. We further showed that catalytic activity toward phosphatidylcholine but not phosphatidylglycerol is directly linked to hemolytic potential of PlaB. Although the function of the prolonged PlaB C terminus remains to be elucidated, it is essential for lipolysis, since the removal of 15 amino acids already abolishes enzyme activity. Additionally, we determined that PlaB preferentially hydrolyzes long-chain fatty acid substrates containing 12 or more carbon atoms. Since phospholipases play an important role as bacterial virulence factors, we examined cell-associated enzymatic activities among L. pneumophila clinical isolates and non-pneumophila species. All tested clinical isolates showed comparable activities, whereas of the non-pneumophila species, only Legionella gormanii and Legionella spiritensis possessed lipolytic activities similar to those of L. pneumophila and comprised plaB-like genes. Interestingly, phosphatidylcholine-specific phospholipase A activity and hemolytic potential were more pronounced in L. pneumophila. Therefore, hydrolysis of the eukaryotic membrane constituent phosphatidylcholine triggered by PlaB could be an important virulence tool for Legionella pathogenicity.
authors.affiliation: Division of Bacterial Infections, FG11, Robert Koch-Institut, Burgstrasse 37, Wernigerode 38855, Germany.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Bender
authors.forename: Kerstin
authors.initials: K
authors.lastname: Rydzewski
authors.forename: Markus
authors.initials: M
authors.lastname: Broich
authors.forename: Eva
authors.initials: E
authors.lastname: Schunder
authors.forename: Klaus
authors.initials: K
authors.lastname: Heuner
authors.forename: Antje
authors.initials: A
authors.lastname: Flieger
mesh_terms: D000595:Amino Acid Sequence; D055162:Biocatalysis; D020134:Catalytic Domain; D005227:Fatty Acids / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006461:Hemolysis; D006801:Humans; D006868:Hydrolysis; D016952:Legionella pneumophila / Q000201:enzymology* / Q000378:metabolism; D007877:Legionnaires' Disease / Q000378:metabolism; D008066:Lipolysis; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D010741:Phospholipases A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013379:Substrate Specificity; D020298:U937 Cells
chemical_list: D005227:Fatty Acids; D010713:Phosphatidylcholines; D010741:Phospholipases A