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

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