1. Department of Biochemistry and Molecular Biophysics, and,
2. Howard Hughes Medical Institute, Columbia University, 650 West 168th Street, New York, New York 10032, USA
3. Suntory Institute for Bioorganic Research, Wakayamadai, Shimamoto-cho, Misima-gun, Osaka 618-8503, Japan
4. These authors contributed equally to this work.
5. Present addresses: Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, New York 10021, USA (O.B.); National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, Maryland 20892, USA (R.M.R.); Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA (D.Y.); Vollum Institute and Howard Hughes Medical Institute, Oregon Health and Science University, Portland, Oregon 97239, USA (E.G.).

Correspondence to: Eric Gouaux^1,2,5 Correspondence and requests for materials should be addressed to E.G. (Email: gouauxe@ohsu.edu).

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 Glt_Ph, a sodium (Na⁺)-coupled aspartate transporter, defining sites for aspartate, two sodium ions and d,l-threo--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 -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.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.