An Outer Membrane Enzyme Encoded by Salmonella typhimurium lpxR That Removes the 3′-Acyloxyacyl Moiety of Lipid A

• Published in: The Journal of biological chemistry 2006-08, Vol.281 (31), p.21974-21987
• Main Authors: Reynolds, C. Michael, Ribeiro, Anthony A., McGrath, Sara C., Cotter, Robert J., Raetz, Christian R.H., Trent, M. Stephen
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Carboxylic Ester Hydrolases - genetics; Carboxylic Ester Hydrolases - metabolism; Escherichia coli; Gene Library; Helicobacter pylori; Lipid A - metabolism; Mass Spectrometry; Membrane Proteins - genetics; Membrane Proteins - metabolism; Molecular Sequence Data; Protein Sorting Signals; Salmonella typhimurium; Salmonella typhimurium - enzymology; Vibrio cholerae; Yersinia enterocolitica
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M603527200

The Salmonella and related bacteria modify the structure of the lipid A portion of their lipopolysaccharide in response to environmental stimuli. Some lipid A modifications are required for virulence and resistance to cationic antimicrobial peptides. We now demonstrate that membranes of Salmonella typhimurium contain a novel hydrolase that removes the 3′-acyloxyacyl residue of lipid A in the presence of 5 mm Ca2+. We have identified the gene encoding the S. typhimurium lipid A 3′-O-deacylase, designated lpxR, by screening an ordered S. typhimurium genomic DNA library, harbored in Escherichia coli K-12, for expression of Ca2+-dependent 3′-O-deacylase activity in membranes. LpxR is synthesized with an N-terminal type I signal peptide and is localized to the outer membrane. Mass spectrometry was used to confirm the position of lipid A deacylation in vitro and the release of the intact 3′-acyloxyacyl group. Heterologous expression of lpxR in the E. coli K-12 W3110, which lacks lpxR, resulted in production of significant amounts of 3′-O-deacylated lipid A in growing cultures. Orthologues of LpxR are present in the genomes of E. coli 0157:H7, Yersinia enterocolitica, Helicobacter pylori, and Vibrio cholerae. The function of LpxR is unknown, but it could play a role in pathogenesis because it might modulate the cytokine response of an infected animal.