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Molecular mechanism of elongation factor 1A inhibition by a Legionella pneumophila glycosyltransferase.

ABSTRACT: Legionnaires' disease is caused by a lethal colonization of alveolar macrophages with the Gram-negative bacterium Legionella pneumophila. LpGT (L. pneumophila glucosyltransferase; also known as Lgt1) has recently been identified as a virulence factor, shutting down protein synthesis in the human cell by specific glucosylation of EF1A (elongation factor 1A), using an unknown mode of substrate recognition and a retaining mechanism for glycosyl transfer. We have determined the crystal structure of LpGT in complex with substrates, revealing a GT-A fold with two unusual protruding domains. Through structure-guided mutagenesis of LpGT, several residues essential for binding of the UDP-glucose-donor and EF1A-acceptor substrates were identified, which also affected L. pneumophila virulence as demonstrated by microinjection studies. Together, these results suggested that a positively charged EF1A loop binds to a negatively charged conserved groove on the LpGT structure, and that two asparagine residues are essential for catalysis. Furthermore, we showed that two further L. pneumophila glycosyltransferases possessed the conserved UDP-glucose-binding sites and EF1A-binding grooves, and are, like LpGT, translocated into the macrophage through the Icm/Dot (intracellular multiplication/defect in organelle trafficking) system.

SUBMITTER: Hurtado-Guerrero R

PROVIDER: S-EPMC3518269 | biostudies-literature | 2010 Feb

REPOSITORIES: biostudies-literature

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Molecular mechanism of elongation factor 1A inhibition by a Legionella pneumophila glycosyltransferase.

Hurtado-Guerrero Ramon R Zusman Tal T Pathak Shalini S Ibrahim Adel F M AF Shepherd Sharon S Prescott Alan A Segal Gil G van Aalten Daan M F DM

The Biochemical journal 20100224 3

Legionnaires' disease is caused by a lethal colonization of alveolar macrophages with the Gram-negative bacterium Legionella pneumophila. LpGT (L. pneumophila glucosyltransferase; also known as Lgt1) has recently been identified as a virulence factor, shutting down protein synthesis in the human cell by specific glucosylation of EF1A (elongation factor 1A), using an unknown mode of substrate recognition and a retaining mechanism for glycosyl transfer. We have determined the crystal structure of ...[more]

PMID: 20030628

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Project description:Several novel Legionella pneumophila virulence genes were previously discovered by use of signature-tagged mutagenesis (P. H. Edelstein, M. A. Edelstein, F. Higa, and S. Falkow, Proc. Natl. Acad. Sci. 96:8190-8195, 1999). One of these mutants appeared to be defective in multiplication in guinea pig lungs and spleens, yet it multiplies normally in guinea pig alveolar macrophages. Here we report further characterization of the mutated gene and its protein and the virulence role of the gene. The complete sequence of the gene, now called lvgA, is 627 bp long, and its protein product is approximately 27 kDa in size. lvgA was present in all 50 strains of L. pneumophila tested. No significant nucleic acid or protein homology was found in the GenBank database for the gene, nor were any distinctive motifs discovered in a search of other databases. The expression of both DotA and IcmX in the lvgA mutant was normal. Subcellular fractionation studies localized LvgA to the outer membrane fraction, and protease digestion studies suggested that at least some of the protein is surface expressed. No change in bacterial lipopolysaccharide composition or reactivity to serogroup-specific antisera was detected in the mutant. Growth competition studies with alveolar macrophages showed that the mutant was outcompeted by its parent 3-fold in 24 h and 24-fold in 48 h, in contrast to what was observed with the null phenotype in parallel testing with alveolar macrophages or with the A549 alveolar epithelial cell line. This macrophage defect of the mutant bacterium was due to slower growth, as the mutant invaded alveolar macrophages normally. Electron microscopy showed that the mutant bacterium resided in a ribosome-studded phagosome in alveolar macrophages, with no distinction from its parent. The lvgA mutant was outcompeted by its parent about sixfold in guinea pig lungs and spleens; prolonged observation of infected animals showed no late-onset virulence of the mutant. Transcomplementation of the mutant restored the parental phenotype in guinea pigs. The lvgA mutant was twofold more susceptible to killing by human beta-defensin 2 but not to killing by other cationic peptides, serum complement, or polymorphonuclear neutrophils. lvgA is a novel virulence gene that is responsible for pleiotropic functions involving both extracellular and intracellular bacterial resistance mechanisms.

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Molecular mechanism of elongation factor 1A inhibition by a Legionella pneumophila glycosyltransferase.

Publications

Molecular mechanism of elongation factor 1A inhibition by a Legionella pneumophila glycosyltransferase.

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