Publications

• Kinetics and phospholipid specificity of apolipoprotein N-acyltransferase.

  Hillmann F., Argentini M., Buddelmeijer N.

  The enzyme apolipoprotein N-acyltransferase (Lnt) is an integral membrane protein that catalyzes the last step in the post-translational modification of bacterial lipoproteins. Lnt undergoes covalent modification in the presence of phospholipids resulting in a thioester acyl-enzyme intermediate. I ... >> More

  The enzyme apolipoprotein N-acyltransferase (Lnt) is an integral membrane protein that catalyzes the last step in the post-translational modification of bacterial lipoproteins. Lnt undergoes covalent modification in the presence of phospholipids resulting in a thioester acyl-enzyme intermediate. It then transfers the acyl chain to the α-amino group of the N-terminal diacylglyceryl-modified cysteine of apolipoprotein, leading to the formation of mature triacylated lipoprotein. To gain insight into the catalytic mechanism of this two-step reaction, we overproduced and purified the enzyme of Escherichia coli and studied its N-acyltransferase activity using a novel in vitro assay. The purified enzyme was fully active, as judged by its ability to form a stable thioester acyl-enzyme intermediate and N-acylate the apo-form of the murein lipoprotein Lpp in vitro. Incorporation of [(3)H]palmitate and mass spectrometry analysis demonstrated that Lnt recognized the synthetic diacylglyceryl-modified lipopeptide FSL-1 as a substrate in a mixed micelle assay. Kinetics of Lnt using phosphatidylethanolamine as an acyl donor and FSL-1 as a substrate were consistent with a ping-pong type mechanism, demonstrating slow acyl-enzyme intermediate formation and rapid N-acyl transfer to the apolipopeptide in vitro. In contrast to earlier in vitro observations, the N-acyltransferase activity was strongly affected by the phospholipid headgroup and acyl chain composition. << Less

  J. Biol. Chem. 286:27936-27946(2011) [PubMed] [EuropePMC]

• Depletion of apolipoprotein N-acyltransferase causes mislocalization of outer membrane lipoproteins in Escherichia coli.

  Robichon C., Vidal-Ingigliardi D., Pugsley A.P.

  Lipoproteins in Gram-negative Enterobacteriaceae carry three fatty acids on the N-terminal cysteine residue, two as a diacylglyceride and one through an N-linkage following signal peptide cleavage. Most lipoproteins are anchored in the outer membrane, facing the periplasm, but some lipoproteins re ... >> More

  Lipoproteins in Gram-negative Enterobacteriaceae carry three fatty acids on the N-terminal cysteine residue, two as a diacylglyceride and one through an N-linkage following signal peptide cleavage. Most lipoproteins are anchored in the outer membrane, facing the periplasm, but some lipoproteins remain in the plasma membrane, depending on the amino acid at position +2, immediately after the fatty-acylated cysteine. In vitro, the last step in lipoprotein maturation, N-acylation of apolipoproteins by the plasma membrane apolipoprotein N-acyltransferase (Lnt), is necessary for efficient recognition of outer membrane lipoproteins by the Lol system, which transports them from the plasma to the outer membrane (Fukuda, A., Matsuyama, S.-I., Hara, T., Nakayama, J., Nagasawa, H., and Tokuda, H. (2002) J. Biol. Chem. 277, 43512-43518). To study the role of Lnt in vivo, we constructed a conditional lnt mutant of Escherichia coli. The apo-form of peptidoglycan-anchored major lipoprotein (Lpp) and two other outer membrane lipoproteins accumulated in the plasma membrane when lnt expression was reduced. We also found that Lnt is an essential protein in E. coli and that the lethality is partially because of the retention of apoLpp in the plasma membrane. Topology mapping of Lnt with beta-galactosidase and alkaline phosphatase fusions indicated the presence of six membrane-spanning segments. The lnt gene in a mutant of Salmonella enterica displaying thermosensitive Lnt activity (Gupta, S. D., Gan, K., Schmid, M. B., and Wu, H. C. (1993) J. Biol. Chem. 268, 16551-16556) was found to carry a mutation causing a single glutamate to lysine substitution at a highly conserved position in the last predicted periplasmic loop of the protein. << Less

  J. Biol. Chem. 280:974-983(2005) [PubMed] [EuropePMC]

• Identification and subcellular localization of apolipoprotein N-acyltransferase in Escherichia coli.

  Gupta S.D., Wu H.C.

  Apolipoprotein N-acyltransferase, the enzyme catalyzing the conversion of apolipoprotein to mature lipoprotein, was detected by an in vitro assay using [35S]methionine-labeled apolipoprotein as the substrate. Triton X-100 solubilized the enzyme, and was required for its activity. The enzyme showed ... >> More

  Apolipoprotein N-acyltransferase, the enzyme catalyzing the conversion of apolipoprotein to mature lipoprotein, was detected by an in vitro assay using [35S]methionine-labeled apolipoprotein as the substrate. Triton X-100 solubilized the enzyme, and was required for its activity. The enzyme showed a broad pH optimum (pH 6.5-7.5). N-Acylation of apolipoprotein with ethanol-washed membranes was dependent on exogenous phospholipids, with phosphatidylethanolamine, phosphatidylglycerol and cardiolipin all showing about 10-to 20-times enhancement of the enzyme activity in the delipidated membranes. Incubation of apolipoprotein with [3H]palmitate-labeled membranes resulted in the incorporation of [3H]palmitate into lipoprotein. The enzyme was found to be enriched in the inner membrane and in the inner membrane/outer membrane mixed fractions of the E. coli cell envelope. << Less

  FEMS Microbiol. Lett. 62:37-41(1991) [PubMed] [EuropePMC]