Crystal structure of the outer membrane active transporter FepA from Escherichia coli

Susan K. Buchanan, Barbara S. Smith, Lalitha Venkatramani, Di Xia, Lothar Esser, Maya Palnitkar, Ranjan Chakraborty, Dick Van Der Helm, Johann Deisenhofer

Research output: Contribution to journalArticlepeer-review

497 Scopus citations


Integral outer membrane receptors for iron chelates and vitamin B12 carry out specific ligand transport against a concentration gradient. Energy for active transport is obtained from the proton-motive force of the inner membrane through physical interaction with TonB-ExbB-ExbD, an inner membrane complex. Here we report the crystal structure of an active transport, outer membrane receptor at 2.4 Å resolution. Two distinct functional domains are revealed: (i) a 22-stranded β-barrel that spans the outer membrane and contains large extracellular loops which appear to function in ligand binding; and (ii) a globular N-terminal domain that folds into the barrel pore, inhibiting access to the periplasm and contributing two additional loops for potential ligand binding. These loops could provide a signaling pathway between the processes of ligand recognition and TonB-mediated transport. The blockage of the pore suggests that the N-terminal domain must undergo a conformational rearrangement to allow ligand transport into the periplasm.

Original languageEnglish (US)
Pages (from-to)56-63
Number of pages8
JournalNature Structural Biology
Issue number1
StatePublished - 1999

ASJC Scopus subject areas

  • Structural Biology
  • Biochemistry
  • Genetics


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