Structure of the formate transporter FocA reveals a pentameric aquaporin-like channel

Nature. 2009 Nov 26;462(7272):467-72. doi: 10.1038/nature08610.


FocA is a representative member of the formate-nitrite transporter family, which transports short-chain acids in bacteria, archaea, fungi, algae and parasites. The structure and transport mechanism of the formate-nitrite transporter family remain unknown. Here we report the crystal structure of Escherichia coli FocA at 2.25 A resolution. FocA forms a symmetric pentamer, with each protomer consisting of six transmembrane segments. Despite a lack of sequence homology, the overall structure of the FocA protomer closely resembles that of aquaporin and strongly argues that FocA is a channel, rather than a transporter. Structural analysis identifies potentially important channel residues, defines the channel path and reveals two constriction sites. Unlike aquaporin, FocA is impermeable to water but allows the passage of formate. A structural and biochemical investigation provides mechanistic insights into the channel activity of FocA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aquaporins / chemistry*
  • Aquaporins / metabolism
  • Crystallography, X-Ray
  • Escherichia coli / chemistry
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism
  • Formates / metabolism
  • Liposomes / chemistry
  • Liposomes / metabolism
  • Membrane Transport Proteins / chemistry*
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism
  • Models, Molecular
  • Molecular Mimicry
  • Mutation
  • Permeability
  • Protein Structure, Quaternary
  • Structure-Activity Relationship
  • Water / analysis
  • Water / metabolism


  • Aquaporins
  • Escherichia coli Proteins
  • FocA protein, E coli
  • Formates
  • Liposomes
  • Membrane Transport Proteins
  • Water
  • formic acid

Associated data

  • PDB/3KCU
  • PDB/3KCV