TY - JOUR
T1 - A Leptospira interrogans enzyme with similarity to yeast Ste14p that methylates the 1-phosphate group of lipid A
AU - Hinckley, Middleton Boon
AU - Reynolds, C. Michael
AU - Ribeiro, Anthony A.
AU - McGrath, Sara C.
AU - Cotter, Robert J.
AU - Lauw, Fanny N.
AU - Golenbock, Douglas T.
AU - Raetz, Christian R.H.
PY - 2005/8/26
Y1 - 2005/8/26
N2 - 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′-32P]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.
AB - 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′-32P]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.
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U2 - 10.1074/jbc.M506103200
DO - 10.1074/jbc.M506103200
M3 - Article
C2 - 15994324
AN - SCOPUS:24044511808
SN - 0021-9258
VL - 280
SP - 30214
EP - 30224
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 34
ER -