Modification of the lipid A domain of lipopolysaccharide (LPS) is important for the pathogenesis and virulence of various Gram-negative bacteria. The major lipid A species of Helicobacter pylori is significantly different from that of Escherichia coli. H. pylori lipid A contains fewer acyl chains and phosphate groups with only one Kdo sugar attached to the disaccharide backbone. However, H. pylori produces a minor lipid A species that resembles E. coli lipid A, suggesting that the major lipid A species results from the action of specific modifying enzymes. This work describes two enzymes, a lipid A phosphatase and a phosphoethanolamine (pEtN) transferase, involved in modifying the 1-position of H. pylori lipid A. H. pylori lipid A contains a pEtN unit directly linked to the 1-position of the disaccharide backbone. This is in contrast to the pEtN units found in other pathogens, which are attached to the lipid A phosphate group to form a pyrophosphate linkage. Using in-vitro assay systems, we demonstrate that the modification of the 1-position of H. pylori lipid A is a two-step process involving the removal of the 1-phosphate group by LpxEHP followed by the addition of a pEtN residue catalyzed by EptAHP. As compared to wild-type H. pylori, lpxEHP mutants are extremely sensitive to the cationic peptide polymyxin, thus, demonstrating the importance of modifying the 1-position of lipid A. Furthermore, this work describes another enzyme, YeiU (renamed LpxT), which specifically utilizes the carrier lipid undecaprenyl pyrophsphate (C55-PP) to modify the 1-position of E. coli lipid A. Typically, E. coli lipid A is a hexa-acylated disaccharide of glucosamine in which monophosphate groups are attached at positions 1 and 4'; however, a small fraction contains a diphosphate moiety at the 1-position (lipid A 1-diphosphate). 32P-labeled lipid A obtained from lpxT deficient mutants produces only lipid A, and complementation with a plasmid expressing LpxT restores lipid A 1-diphosphate formation. Inhibition of lipid A 1-diphosphate synthesis was demonstrated by sequestering C55-PP with the cyclic polypeptide antibiotic bacitracin. In conclusion, this work describes two novel pathways for lipid A modification at the 1-position in Gram-negative bacteria.
","abstract_html":"<p>Modification of the lipid A domain of lipopolysaccharide (LPS) is important for the pathogenesis and virulence of various Gram-negative bacteria. The major lipid A species of <em>Helicobacter pylori</em> is significantly different from that of <em>Escherichia coli</em>. <em>H. pylori</em> lipid A contains fewer acyl chains and phosphate groups with only one Kdo sugar attached to the disaccharide backbone. However, <em>H. pylori</em> produces a minor lipid A species that resembles <em>E. coli</em> lipid A, suggesting that the major lipid A species results from the action of specific modifying enzymes. This work describes two enzymes, a lipid A phosphatase and a phosphoethanolamine (pEtN) transferase, involved in modifying the 1-position of <em>H. pylori</em> lipid A. <em>H. pylori</em> lipid A contains a pEtN unit directly linked to the 1-position of the disaccharide backbone. This is in contrast to the pEtN units found in other pathogens, which are attached to the lipid A phosphate group to form a pyrophosphate linkage. Using <em>in-vitro</em> assay systems, we demonstrate that the modification of the 1-position of <em>H. pylori</em> lipid A is a two-step process involving the removal of the 1-phosphate group by LpxE<sub>HP</sub> followed by the addition of a pEtN residue catalyzed by EptA<sub>HP</sub>. As compared to wild-type <em>H. pylori</em>, <em>lpxE<sub>HP</sub><em> mutants are extremely sensitive to the cationic peptide polymyxin, thus, demonstrating the importance of modifying the 1-position of lipid A. Furthermore, this work describes another enzyme, YeiU (renamed LpxT), which specifically utilizes the carrier lipid undecaprenyl pyrophsphate (C<sub>55</sub>-PP) to modify the 1-position of <em>E. coli</em> lipid A. Typically, <em>E. coli</em> lipid A is a hexa-acylated disaccharide of glucosamine in which monophosphate groups are attached at positions 1 and 4'; however, a small fraction contains a diphosphate moiety at the 1-position (lipid A 1-diphosphate). <sup>32</sup>P-labeled lipid A obtained from <em>lpxT</em> deficient mutants produces only lipid A, and complementation with a plasmid expressing LpxT restores lipid A 1-diphosphate formation. Inhibition of lipid A 1-diphosphate synthesis was demonstrated by sequestering C<sub>55</sub>-PP with the cyclic polypeptide antibiotic bacitracin. In conclusion, this work describes two novel pathways for lipid A modification at the 1-position in Gram-negative bacteria.</p>","abstract_has_math":false,"creators":["Tran, An Xuong"],"institution":null,"degree_name":"PhD (Doctor of Philosophy)","degree_level":"Dissertation - restricted","degree_discipline":"Biomedical Sciences","degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2007,"date_issued":"2007-05-05T07:00:00Z","date_published":"2007-05-05T07:00:00Z","updated_at":"2026-07-24T02:21:19Z","subjects":["LPS","Lipid A","Endotoxin","Phosphatase","Phosphoethanolamine","Cationic antimicrobial peptides","Phosphotransferase","Chemicals and Drugs","Enzymes and Coenzymes","Medicine and Health Sciences"],"languages":[],"rights":["Copyright by the authors."],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://dc.etsu.edu/etd/2036","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Tran, An Xuong"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2007-05-05T07:00:00Z"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Biomedical Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation - restricted"]},{"key":"thesis:degree_name","label":"Degree Name","values":["PhD (Doctor of Philosophy)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["LPS","Lipid A","Endotoxin","Phosphatase","Phosphoethanolamine","Cationic antimicrobial peptides","Phosphotransferase","Chemicals and Drugs","Enzymes and Coenzymes","Medicine and Health Sciences"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:rights","label":"Dc Rights","values":["Copyright by the authors."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://dc.etsu.edu/context/etd/article/3397/viewcontent/TranA030807f.pdf","https://dc.etsu.edu/etd/2036"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Modification of the lipid A domain of lipopolysaccharide (LPS) is important for the pathogenesis and virulence of various Gram-negative bacteria. The major lipid A species of Helicobacter pylori is significantly different from that of Escherichia coli. H. pylori lipid A contains fewer acyl chains and phosphate groups with only one Kdo sugar attached to the disaccharide backbone. However, H. pylori produces a minor lipid A species that resembles E. coli lipid A, suggesting that the major lipid A species results from the action of specific modifying enzymes. This work describes two enzymes, a lipid A phosphatase and a phosphoethanolamine (pEtN) transferase, involved in modifying the 1-position of H. pylori lipid A. H. pylori lipid A contains a pEtN unit directly linked to the 1-position of the disaccharide backbone. This is in contrast to the pEtN units found in other pathogens, which are attached to the lipid A phosphate group to form a pyrophosphate linkage. Using in-vitro assay systems, we demonstrate that the modification of the 1-position of H. pylori lipid A is a two-step process involving the removal of the 1-phosphate group by LpxEHP followed by the addition of a pEtN residue catalyzed by EptAHP. As compared to wild-type H. pylori, lpxEHP mutants are extremely sensitive to the cationic peptide polymyxin, thus, demonstrating the importance of modifying the 1-position of lipid A. Furthermore, this work describes another enzyme, YeiU (renamed LpxT), which specifically utilizes the carrier lipid undecaprenyl pyrophsphate (C55-PP) to modify the 1-position of E. coli lipid A. Typically, E. coli lipid A is a hexa-acylated disaccharide of glucosamine in which monophosphate groups are attached at positions 1 and 4'; however, a small fraction contains a diphosphate moiety at the 1-position (lipid A 1-diphosphate). 32P-labeled lipid A obtained from lpxT deficient mutants produces only lipid A, and complementation with a plasmid expressing LpxT restores lipid A 1-diphosphate formation. Inhibition of lipid A 1-diphosphate synthesis was demonstrated by sequestering C55-PP with the cyclic polypeptide antibiotic bacitracin. In conclusion, this work describes two novel pathways for lipid A modification at the 1-position in Gram-negative bacteria.
"]},{"key":"dc:title","label":"Title","values":["Periplasmic Modification of the 1-Phosphate Group of Lipid A in Gram-Negative Bacteria."]}]}],"canonical_facts":{"dc:creator":["Tran, An Xuong"],"dc:date.issued":["2007-05-05T07:00:00Z"],"dc:description.abstract":["Modification of the lipid A domain of lipopolysaccharide (LPS) is important for the pathogenesis and virulence of various Gram-negative bacteria. The major lipid A species of Helicobacter pylori is significantly different from that of Escherichia coli. H. pylori lipid A contains fewer acyl chains and phosphate groups with only one Kdo sugar attached to the disaccharide backbone. However, H. pylori produces a minor lipid A species that resembles E. coli lipid A, suggesting that the major lipid A species results from the action of specific modifying enzymes. This work describes two enzymes, a lipid A phosphatase and a phosphoethanolamine (pEtN) transferase, involved in modifying the 1-position of H. pylori lipid A. H. pylori lipid A contains a pEtN unit directly linked to the 1-position of the disaccharide backbone. This is in contrast to the pEtN units found in other pathogens, which are attached to the lipid A phosphate group to form a pyrophosphate linkage. Using in-vitro assay systems, we demonstrate that the modification of the 1-position of H. pylori lipid A is a two-step process involving the removal of the 1-phosphate group by LpxEHP followed by the addition of a pEtN residue catalyzed by EptAHP. As compared to wild-type H. pylori, lpxEHP mutants are extremely sensitive to the cationic peptide polymyxin, thus, demonstrating the importance of modifying the 1-position of lipid A. Furthermore, this work describes another enzyme, YeiU (renamed LpxT), which specifically utilizes the carrier lipid undecaprenyl pyrophsphate (C55-PP) to modify the 1-position of E. coli lipid A. Typically, E. coli lipid A is a hexa-acylated disaccharide of glucosamine in which monophosphate groups are attached at positions 1 and 4'; however, a small fraction contains a diphosphate moiety at the 1-position (lipid A 1-diphosphate). 32P-labeled lipid A obtained from lpxT deficient mutants produces only lipid A, and complementation with a plasmid expressing LpxT restores lipid A 1-diphosphate formation. Inhibition of lipid A 1-diphosphate synthesis was demonstrated by sequestering C55-PP with the cyclic polypeptide antibiotic bacitracin. In conclusion, this work describes two novel pathways for lipid A modification at the 1-position in Gram-negative bacteria.
"],"dc:identifier":["https://dc.etsu.edu/context/etd/article/3397/viewcontent/TranA030807f.pdf","https://dc.etsu.edu/etd/2036"],"dc:rights":["Copyright by the authors."],"dc:subject":["LPS","Lipid A","Endotoxin","Phosphatase","Phosphoethanolamine","Cationic antimicrobial peptides","Phosphotransferase","Chemicals and Drugs","Enzymes and Coenzymes","Medicine and Health Sciences"],"dc:title":["Periplasmic Modification of the 1-Phosphate Group of Lipid A in Gram-Negative Bacteria."],"thesis:degree_discipline":["Biomedical Sciences"],"thesis:degree_level":["Dissertation - restricted"],"thesis:degree_name":["PhD (Doctor of Philosophy)"]},"updated_at":"2026-07-24T02:21:19Z"}