Nucleotide substrate recognition by UDP-N-acetylglucosamine acyltransferase (LpxA) in the first step of lipid A biosynthesis

Venkatasubramanian Ulaganathan, Lori Buetow, William N. Hunter

    Research output: Contribution to journalArticlepeer-review

    27 Citations (Scopus)


    Lipid A is an integral component of the lipopolysaccharide (LPS) that forms the selective and protective outer monolayer of Gram-negative bacteria, and is essential for bacterial growth and viability. UDP-N-acetylglucosamine acyltransferase (LpxA) initiates lipid A biosynthesis by catalyzing the transfer of R-3-hydroxymyristic acid from acyl carrier protein to the 3'-hydroxyl group of UDP-GlcNAc. The enzyme is a homotrimer, and previous studies suggested that the active site lies within a positively charged cleft formed at the subunit-subunit interface. The crystal structure of Escherichia coli LpxA in complex with UDP-GlcNAc reveals details of the substrate-binding site, with prominent hydrophilic interactions between highly conserved clusters of residues (Asn198, Glu200, Arg204 and Arg205) with UDP, and (Asp74, His125, His144 and Gln161) with the GlcNAc moiety. These interactions serve to bind and orient the substrate for catalysis. The crystallographic model supports previous results, which suggest that acylation occurs via nucleophilic attack of deprotonated UDP-GlcNAc on the acyl donor in a general base-catalyzed mechanism involving a catalytic dyad of His125 and Asp126. His125, the general base, interacts with the 3'-hydroxyl group of UDP-GlcNAc to generate the nucleophile. The Asp126 side-chain accepts a hydrogen bond from His125 and helps orient the general base to participate in catalysis. Comparisons with an LpxA:peptide inhibitor complex indicate that the peptide competes with both nucleotide and acyl carrier protein substrates.

    Original languageEnglish
    Pages (from-to)305-312
    Number of pages8
    JournalJournal of Molecular Biology
    Issue number2
    Publication statusPublished - 1 Jun 2007


    • Acetylglucosamine
    • Acyltransferases
    • Amino Acid Sequence
    • Binding Sites
    • Crystallography, X-Ray
    • Escherichia coli Proteins
    • Lipid A
    • Models, Molecular
    • Molecular Sequence Data
    • Molecular Structure
    • Nucleotides
    • Protein Structure, Quaternary
    • Protein Structure, Secondary
    • Substrate Specificity
    • Uridine Diphosphate


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