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Lipopolysaccharide (LPS) is one of the main constituents of the Gram-negative bacterial outer membrane. It usually consists of a highly variable O-antigen, a less variable core oligosaccharide, and a highly conserved lipid moiety, designated lipid A. Several bacteria are capable of modifying their lipid A architecture in response to external stimuli. The outer membrane-localized lipid A 3-O-deacylase, encoded by the pagL gene of Salmonella enterica serovar Typhimurium, removes the fatty acyl chain from the 3 position of lipid A. Although a similar activity was reported in some other Gram-negative bacteria, the corresponding genes could not be identified. Here, we describe the presence of pagL homologs in a variety of Gram-negative bacteria. Although the overall sequence similarity is rather low, a conserved domain could be distinguished in the C-terminal region. The activity of the Pseudomonas aeruginosa and Bordetella bronchiseptica pagL homologs was confirmed upon expression in Escherichia coli, which resulted in the removal of an R-3-hydroxymyristoyl group from lipid A. Upon deacylation by PagL, E. coli lipid A underwent another modification, which was the result of the activity of the endogenous palmitoyl transferase PagP. Furthermore, we identified a conserved histidine-serine couple as active site residues, suggesting a catalytic mechanism similar to serine hydrolases. The biological function of PagL remains unclear. However, because PagL homologs were found in both pathogenic and nonpathogenic species, PagL-mediated deacylation of lipid A probably does not have a dedicated role in pathogenicity.

Lipopolysaccharide, Pseudomonas aeruginosa, Escherichia coli, lipid A, Salmonella enterica, gram negative bacteria, Bordetella bronchiseptica

NCBI PubMed ID: 15611102
Publication DOI: 10.1074/jbc.M414235200
Journal NLM ID: 2985121R
Publisher: Baltimore, MD: American Society for Biochemistry and Molecular Biology
Correspondence: j.j.g.geurtsen

bio.uu.nl
Institutions: Department of Molecular Microbiology, Utrecht University, Padualaan 8, Utrecht 3584 CH, The Netherlands, Netherlands Vaccine Institute, P. O. Box 457, Bilthoven 3720 AL, The Netherlands, Laboratory of Immunotherapy, University Medical Center, P. O. Box 85090, Utrecht 3508 AB, The Netherlands, Laboratory of Organic-Analytical Chemistry, National Institute of Public Health and the Environment, P. O. Box 1, Bilthoven 3720 BA, The Netherlands
Methods: PCR, GC-MS, DNA techniques, ESI-MS, genetic methods, tricine-SDS-PAGE, immunoblotting