Structures of aminoarabinose transferase ArnT suggest a molecular basis for lipid A glycosylation

Science. 2016 Feb 5;351(6273):608-12. doi: 10.1126/science.aad1172.


Polymyxins are antibiotics used in the last line of defense to combat multidrug-resistant infections by Gram-negative bacteria. Polymyxin resistance arises through charge modification of the bacterial outer membrane with the attachment of the cationic sugar 4-amino-4-deoxy-l-arabinose to lipid A, a reaction catalyzed by the integral membrane lipid-to-lipid glycosyltransferase 4-amino-4-deoxy-L-arabinose transferase (ArnT). Here, we report crystal structures of ArnT from Cupriavidus metallidurans, alone and in complex with the lipid carrier undecaprenyl phosphate, at 2.8 and 3.2 angstrom resolution, respectively. The structures show cavities for both lipidic substrates, which converge at the active site. A structural rearrangement occurs on undecaprenyl phosphate binding, which stabilizes the active site and likely allows lipid A binding. Functional mutagenesis experiments based on these structures suggest a mechanistic model for ArnT family enzymes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Sugars / chemistry
  • Arabinose / analogs & derivatives*
  • Arabinose / chemistry
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / ultrastructure
  • Catalysis
  • Catalytic Domain
  • Crystallography, X-Ray
  • Cupriavidus / enzymology*
  • Glycosylation
  • Lipid A / chemistry*
  • Mutagenesis
  • Mutation
  • Pentosyltransferases / chemistry*
  • Pentosyltransferases / genetics
  • Pentosyltransferases / ultrastructure
  • Polyisoprenyl Phosphates / chemistry
  • Polymyxins / chemistry
  • Protein Binding
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Substrate Specificity


  • Amino Sugars
  • Bacterial Proteins
  • Lipid A
  • Polyisoprenyl Phosphates
  • Polymyxins
  • aminoarabinose
  • undecaprenyl phosphate
  • 4-amino-4-deoxyarabinose
  • Arabinose
  • Pentosyltransferases

Associated data

  • PDB/5EZM
  • PDB/5F15