The Legionella Autoinducer Synthase LqsA Produces an α-Hydroxyketone Signaling Molecule

Abstract

The opportunistic pathogen Legionella pneumophila replicates in human lung macrophages and in free-living amoebae. To accommodate the transfer between host cells, L. pneumophila switches from a replicative to a transmissive phase. L. pneumophila harbors a gene cluster homologous to the Vibrio cholerae cqsAS quorum sensing system, encoding a putative autoinducer synthase (lqsA) and a sensor kinase (lqsS), which flank a response regulator (lqsR). LqsR is an element of the L. pneumophila virulence regulatory network, which promotes pathogen-host cell interactions and inhibits entry into the replicative growth phase. Here, we show that lqsA functionally complements a V. cholerae cqsA autoinducer synthase deletion mutant and, upon expression in L. pneumophila or Escherichia coli, produces the diffusible signaling molecule LAI-1 (Legionella autoinducer-1). LAI-1 is distinct from CAI-1 (Cholerae autoinducer-1) and was identified as 3-hydroxypentadecan-4-one using liquid chromatography coupled to high resolution tandem mass spectrometry. The activity of both LqsA and CqsA was abolished upon mutation of a conserved lysine, and covalent binding of the cofactor pyridoxal 5-phosphate to this lysine was confirmed by mass spectrometry. Thus, LqsA and CqsA belong to a family of pyridoxal 5-phosphate-dependent autoinducer synthases, which produce the ␣-hydroxyketone signaling molecules LAI-1 and CAI-1.

Molecular Pathogenesis of Infections Caused byLegionella pneumophila

“…The response regulator LqsR contributes to virulence processes such as phagocytosis and the formation of the LCV by relaying signals from the adjacent sensor kinase LqsS (334,335). Neighboring this system is an autoinducer synthase, LqsA, which was recently shown to synthesize 3-hydroxypentadecan-4-one, the small Legionella autoinducer 1 (LAI1) (313). Although an lqsA mutant of L. pneumophila showed only a modest decrease in phagocytosis compared to the wild-type strain, the overexpression of LqsA in an lqsR or lqsS mutant background restored the more severe uptake defects of these mutants, suggesting that LqsA does have a role in modulating virulence, possibly …”

Synergistic Contribution of theLegionella pneumophila lqsGenes to Pathogen-Host Interactions

“…In Escherichia coli, the hdeD gene is localized on an acid fitness island and involved in acid resistance (38,39). LqsA was recently characterized as a pyridoxal 5Ј-phosphate-dependent enzyme producing the diffusible signaling molecule 3-hydroxy-pentadecan-4-one (68). The clustering and orientation of the lqsA-lqsR-lqsS genes are conserved among different bacterial species (70), suggesting a functional relationship among the individual genes.…”

Unstable Reaction Intermediates and Hysteresis during the Catalytic Cycle of 5-Aminolevulinate Synthase

“…ALAS belongs to the ␣-oxoamine synthase family of PLP-dependent enzymes, whose members catalyze a condensation between a small amino acid and an acyl-CoA thioester (1,(5)(6)(7)(8)(9). ALAS is a homodimer with its active site located at the dimeric interface (10).…”