Coupling substrate and ion binding to extracellular gate of a sodium-dependent aspartate transporter

Nature. 2007 Jan 25;445(7126):387-93. doi: 10.1038/nature05455. Epub 2007 Jan 17.


Secondary transporters are integral membrane proteins that catalyse the movement of substrate molecules across the lipid bilayer by coupling substrate transport to one or more ion gradients, thereby providing a mechanism for the concentrative uptake of substrates. Here we describe crystallographic and thermodynamic studies of Glt(Ph), a sodium (Na+)-coupled aspartate transporter, defining sites for aspartate, two sodium ions and d,l-threo-beta-benzyloxyaspartate, an inhibitor. We further show that helical hairpin 2 is the extracellular gate that controls access of substrate and ions to the internal binding sites. At least two sodium ions bind in close proximity to the substrate and these sodium-binding sites, together with the sodium-binding sites in another sodium-coupled transporter, LeuT, define an unwound alpha-helix as the central element of the ion-binding motif, a motif well suited to the binding of sodium and to participation in conformational changes that accompany ion binding and unbinding during the transport cycle.

Publication types

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

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Transport Systems / antagonists & inhibitors
  • Amino Acid Transport Systems / chemistry
  • Amino Acid Transport Systems / genetics
  • Amino Acid Transport Systems / metabolism*
  • Aspartic Acid / metabolism*
  • Aspartic Acid / pharmacology
  • Binding Sites
  • Crystallography, X-Ray
  • Ligands
  • Models, Molecular
  • Mutation / genetics
  • Protein Conformation
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Pyrococcus horikoshii / chemistry*
  • Sodium / metabolism*
  • Sodium / pharmacology*
  • Substrate Specificity
  • Thermodynamics


  • Amino Acid Transport Systems
  • Ligands
  • Protein Subunits
  • benzyloxyaspartate
  • Aspartic Acid
  • Sodium

Associated data

  • PDB/2NWL
  • PDB/2NWW
  • PDB/2NWX