An outer membrane enzyme encoded by Salmonella typhimurium lpxR that removes the 3'-acyloxyacyl moiety of lipid A.
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 O157: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.
Reynolds
C Michael
CM
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710.
Ribeiro
Anthony A
AA
Duke NMR Spectroscopy Center and Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710.
McGrath
Sara C
SC
Middle Atlantic Mass Spectrometry Laboratory, Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Cotter
Robert J
RJ
Middle Atlantic Mass Spectrometry Laboratory, Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Raetz
Christian R H
CRH
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710. Electronic address: raetz@biochem.duke.edu.
Trent
M Stephen
MS
Department of Microbiology, J. H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614. Electronic address: trentms@mail.etsu.edu.
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism*; D015723:Gene Library; D008050:Lipid A / Q000378:metabolism*; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals; D012486:Salmonella typhimurium / Q000201:enzymology*
D001426:Bacterial Proteins; D008050:Lipid A; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D002265:Carboxylic Ester Hydrolases; C513984:LpxR protein, Salmonella typhimurium; C048964:acyloxyacyl hydrolase