Expression cloning and biochemical characterization of a Rhizobium leguminosarum lipid A 1-phosphatase.
Lipid A of Rhizobium leguminosarum, a nitrogen-fixing plant endosymbiont, displays several significant structural differences when compared with Escherichia coli. An especially striking feature of R. leguminosarum lipid A is that it lacks both the 1- and 4'-phosphate groups. Distinct lipid A phosphatases that attack either the 1 or the 4' positions have previously been identified in extracts of R. leguminosarum and Rhizobium etli but not Sinorhizobium meliloti or E. coli. Here we describe the identification of a hybrid cosmid (pMJK-1) containing a 25-kb R. leguminosarum 3841 DNA insert that directs the overexpression of the lipid A 1-phosphatase. Transfer of pMJK-1 into S. meliloti 1021 results in heterologous expression of 1-phosphatase activity, which is normally absent in extracts of strain 1021, and confers resistance to polymyxin. Sequencing of a 7-kb DNA fragment derived from the insert of pMJK-1 revealed the presence of a lipid phosphatase ortholog (designated LpxE). Expression of lpxE in E. coli behind the T7lac promoter results in the appearance of robust 1-phosphatase activity, which is normally absent in E. coli membranes. Matrix-assisted laser-desorption/time of flight and radiochemical analysis of the product generated in vitro from the model substrate lipid IVA confirms the selective removal of the 1-phosphate group. These findings show that lpxE is the structural gene for the 1-phosphatase. The availability of lpxE may facilitate the re-engineering of lipid A structures in diverse Gram-negative bacteria and allow assessment of the role of the 1-phosphatase in R. leguminosarum symbiosis with plants. Possible orthologs of LpxE are present in some intracellular human pathogens, including Francisella tularensis, Brucella melitensis, and Legionella pneumophila.
Karbarz
Mark J
MJ
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
Kalb
Suzanne R
SR
Cotter
Robert J
RJ
Raetz
Christian R H
CR
D000595:Amino Acid Sequence; D001483:Base Sequence; D002240:Carbohydrate Sequence; D003001:Cloning, Molecular; D003360:Cosmids; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D008050:Lipid A / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016961:Rhizobium leguminosarum / Q000201:enzymology* / Q000235:genetics*; D016962:Sinorhizobium meliloti / Q000235:genetics; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D004269:DNA, Bacterial; D008050:Lipid A; D011994:Recombinant Proteins; C478996:lipid A 1-phosphatase, Rhizobium leguminosarum; D010744:Phosphoric Monoester Hydrolases