title: Relaxed acyl chain specificity of Bordetella UDP-N-acetylglucosamine acyltransferases.
abstract: Lipid A (endotoxin) is a major structural component of Gram-negative outer membranes. It also serves as the hydrophobic anchor of lipopolysaccharide and is a potent activator of the innate immune response. Lipid A molecules from the genus Bordetella are reported to exhibit unusual structural asymmetry with respect to the acyl chains at the 3- and 3'-positions. These acyl chains are attached by UDP-N-acetylglucosamine acyltransferase (LpxA). To determine the origin of the acyl variability, the single lpxA ortholog present in each of the genomes of Bordetella bronchiseptica (lpxA(Br)), Bordetella parapertussis (lpxA(Pa)), and Bordetella pertussis (lpxA(Pe)) was cloned and expressed in Escherichia coli. In contrast to all LpxA proteins studied to date, LpxA(Br) and LpxA(Pe) display relaxed acyl chain length specificity in vitro, utilizing C(10)OH-ACP, C(12)OH-ACP, and C(14)OH-ACP at similar rates. Furthermore, hybrid lipid A molecules synthesized at 42 degrees C by an E. coli lpxA mutant complemented with lpxA(Pe) contain C(10)OH, C(12)OH, and C(14)OH at both the 3- and 3'-positions, as determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In contrast, LpxA from B. parapertussis did not display relaxed specificity but was selective for C(10)OH-ACP. This study provides an enzymatic explanation for some of the unusual acyl chain variations found in Bordetella lipid A.
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Sweet
authors.forename: Andrew
authors.initials: A
authors.lastname: Preston
authors.forename: Elinor
authors.initials: E
authors.lastname: Toland
authors.forename: Suzanne M
authors.initials: SM
authors.lastname: Ramirez
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cotter
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: Maskell
authors.forename: Christian R H
authors.initials: CR
authors.lastname: Raetz
mesh_terms: D000217:Acyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001483:Base Sequence; D001884:Bordetella / Q000201:enzymology*; D002240:Carbohydrate Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013379:Substrate Specificity
chemical_list: D017931:DNA Primers; D000217:Acyltransferases; C050304:acyl-(acyl-carrier-protein)-UDP-N-acetylglucosamine acyltransferase