Transmembrane signaling across the ligand-gated FhuA receptor: crystal structures of free and ferrichrome-bound states reveal allosteric changes

Cell. 1998 Dec 11;95(6):771-8. doi: 10.1016/s0092-8674(00)81700-6.


FhuA protein facilitates ligand-gated transport of ferrichrome-bound iron across Escherichia coli outer membranes. X-ray analysis at 2.7 A resolution reveals two distinct conformations in the presence and absence of ferrichrome. The monomeric protein consists of a hollow, 22-stranded, antiparallel beta barrel (residues 160-714), which is obstructed by a plug (residues 19-159). The binding site of ferrichrome, an aromatic pocket near the cell surface, undergoes minor changes upon association with the ligand. These are propagated and amplified across the plug, eventually resulting in substantially different protein conformations at the periplasmic face. Our findings reveal the mechanism of signal transmission and suggest how the energy-transducing TonB complex senses ligand binding.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allosteric Regulation
  • Amino Acid Sequence
  • Bacterial Outer Membrane Proteins / chemistry*
  • Bacterial Outer Membrane Proteins / metabolism*
  • Cell Membrane / metabolism
  • Crystallography, X-Ray
  • Escherichia coli Proteins*
  • Ferrichrome / metabolism*
  • Ligands
  • Molecular Sequence Data
  • Protein Conformation
  • Receptors, Virus / chemistry*
  • Receptors, Virus / metabolism*
  • Signal Transduction*


  • Bacterial Outer Membrane Proteins
  • Escherichia coli Proteins
  • FhuA protein, E coli
  • Ligands
  • Receptors, Virus
  • Ferrichrome

Associated data

  • PDB/1BY3
  • PDB/1BY5