Projection structure of a member of the amino acid/polyamine/organocation transporter superfamily

J Biol Chem. 2008 Nov 28;283(48):33240-8. doi: 10.1074/jbc.M806917200. Epub 2008 Sep 25.


The L-arginine/agmatine antiporter AdiC is a key component of the arginine-dependent extreme acid resistance system of Escherichia coli. Phylogenetic analysis indicated that AdiC belongs to the amino acid/polyamine/organocation (APC) transporter superfamily having sequence identities of 15-17% to eukaryotic and human APC transporters. For functional and structural characterization, we cloned, overexpressed, and purified wild-type AdiC and the point mutant AdiC-W293L, which is unable to bind and consequently transport L-arginine. Purified detergent-solubilized AdiC particles were dimeric. Reconstitution experiments yielded two-dimensional crystals of AdiC-W293L diffracting beyond 6 angstroms resolution from which we determined the projection structure at 6.5 angstroms resolution. The projection map showed 10-12 density peaks per monomer and suggested mainly tilted helices with the exception of one distinct perpendicular membrane spanning alpha-helix. Comparison of AdiC-W293L with the projection map of the oxalate/formate antiporter from Oxalobacter formigenes, a member from the major facilitator superfamily, indicated different structures. Thus, two-dimensional crystals of AdiC-W293L yielded the first detailed view of a transport protein from the APC superfamily at sub-nanometer resolution.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Transport Systems / chemistry*
  • Amino Acid Transport Systems / genetics
  • Amino Acid Transport Systems, Basic / chemistry*
  • Amino Acid Transport Systems, Basic / genetics
  • Animals
  • Antiporters / chemistry*
  • Antiporters / genetics
  • Crystallography, X-Ray / methods
  • Dimerization
  • Escherichia coli / chemistry*
  • Escherichia coli / genetics
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / genetics
  • Humans
  • Oxalobacter formigenes / chemistry
  • Oxalobacter formigenes / genetics
  • Phylogeny*
  • Protein Structure, Quaternary / physiology


  • AdiC protein, E coli
  • Amino Acid Transport Systems
  • Amino Acid Transport Systems, Basic
  • Antiporters
  • Escherichia coli Proteins