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

Olga Boudker, Renae M. Ryan, Dinesh Yernool, Keiko Shimamoto and Eric Gouaux ()
Additional contact information
Olga Boudker: Columbia University
Renae M. Ryan: Columbia University
Dinesh Yernool: Columbia University
Keiko Shimamoto: Suntory Institute for Bioorganic Research
Eric Gouaux: Columbia University

Nature, 2007, vol. 445, issue 7126, 387-393

Abstract: 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.

Date: 2007
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DOI: 10.1038/nature05455

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