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- Title
Coupling substrate and ion binding to extracellular gate of a sodium-dependent aspartate transporter.
- Authors
Boudker, Olga; Ryan, Renae M.; Yernool, Dinesh; Shimamoto, Keiko; Gouaux, Eric
- Abstract
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 GltPh, a sodium (Na+)-coupled aspartate transporter, defining sites for aspartate, two sodium ions and d,l-threo-β-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 α-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.
- Subjects
ASPARTIC acid; EXCITATORY amino acids; SODIUM ions; SODIUM channels; PHYSIOLOGICAL transport of sodium; ION channels
- Publication
Nature, 2007, Vol 445, Issue 7126, p387
- ISSN
0028-0836
- Publication type
Article
- DOI
10.1038/nature05455