Coupling substrate and ion binding to extracellular gate of a sodium-dependent aspartate transporter
Coupling substrate and ion binding to extracellular gate of a sodium-dependent aspartate transporter
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DOI：
10.1038/nature05455
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发表时间：
2007-01-25
期刊：
影响因子：
64.8
通讯作者：
Gouaux, Eric
中科院分区：
文献类型：
--
作者：
Boudker, Olga;Ryan, Renae M.;Gouaux, Eric
二级转运蛋白是整合的膜蛋白，其通过将底物转运偶联至一个或多个离子梯度来催化底物分子穿过脂质双层的移动，从而提供用于底物的集中摄取的机制。在这里，我们描述了晶体学和热力学研究谷氨酰胺（Ph），钠（Na+）-偶联天冬氨酸转运蛋白，定义网站的天冬氨酸，两个钠离子和D，L-苏-β-苄氧基天冬氨酸，抑制剂。我们进一步表明，螺旋发夹2是控制底物和离子进入内部结合位点的细胞外大门。至少有两个钠离子与底物紧密结合，这些钠结合位点与另一种钠偶联转运蛋白LeuT中的钠结合位点一起定义了一个解绕的α-螺旋作为离子结合基序的中心元件，该基序非常适合于钠的结合和参与转运周期中伴随离子结合和解结合的构象变化。
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.