A Leptospira interrogans enzyme with similarity to yeast Ste14p that methylates the 1-phosphate group of lipid A.
Distinct from other spirochetes, cells of Leptospira interrogans contain orthologues of all the Escherichia coli lpx genes required for lipid A biosynthesis, but they synthesize a modified form of lipopolysaccharide that supposedly activates toll-like receptor 2 (TLR2) instead of TLR4. The recent determination of the L. interrogans lipid A structure revealed an unprecedented O-methylation of its 1-phosphate group (Que-Gewirth, N. L. S., Ribeiro, A. A., Kalb, S. R., Cotter, R. J., Bulach, D. M., Adler, B., Saint Girons, I., Werts, C., and Raetz, C. R. H. (2004) J. Biol. Chem. 279, 25420-25429). The enzymatic activity responsible for selective 1-phosphate methylation has not been previously explored. A membrane enzyme that catalyzes the transfer of a methyl group from S-adenosylmethionine (SAM) to the 1-phosphate moiety of E. coli Kdo2-[4'-(32)P]lipid A has now been discovered. The gene encoding this enzyme was identified based on the hypothesis that methylation of a phosphate group is chemically analogous to methylation of a carboxylate moiety at a membrane-water interface. Database searching revealed a candidate gene (renamed lmtA) in L. interrogans showing distant homology to the yeast isoprenylcysteine carboxyl methyltransferase, encoded by sterile-14, which methylates the a-type mating factor. Orthologues of lmtA were not present in E. coli, the lipid A of which normally lacks the 1-phosphomethyl group, or in other spirochetes, which do not synthesize lipid A. Expression of the lmtA gene behind the lac promoter on a low copy plasmid resulted in the appearance of SAM-dependent methyltransferase activity in E. coli inner membranes and methylation of about 30% of the endogenous E. coli lipid A. Inactivation of the ABC transporter MsbA did not inhibit methylation of newly synthesized lipid A. Methylated E. coli lipid A was analyzed by mass spectrometry and NMR spectroscopy to confirm the location of the phosphomethyl group at the 1-position. In human cells, engineered to express the individual TLR subtypes, 1-phosphomethyl-lipid A purified from lmtA-expressing E. coli potently activated TLR4 but not TLR2.
Boon Hinckley
Middleton
M
Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
Reynolds
C Michael
CM
Ribeiro
Anthony A
AA
McGrath
Sara C
SC
Cotter
Robert J
RJ
Lauw
Fanny N
FN
Golenbock
Douglas T
DT
Raetz
Christian R H
CR
D000595:Amino Acid Sequence; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002474:Cell-Free System; D003001:Cloning, Molecular; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007921:Leptospira interrogans / Q000201:enzymology*; D008050:Lipid A / Q000096:biosynthesis / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008562:Membrane Glycoproteins / Q000378:metabolism; D008745:Methylation; D008969:Molecular Sequence Data; D010710:Phosphates / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011496:Protein Methyltransferases / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013053:Spectrophotometry; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors
D008050:Lipid A; D008055:Lipids; D008562:Membrane Glycoproteins; D010710:Phosphates; D011956:Receptors, Cell Surface; D029701:Saccharomyces cerevisiae Proteins; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D012436:S-Adenosylmethionine; D011496:Protein Methyltransferases; C498863:Ste14 protein, S cerevisiae