Boudker Olga, Ryan Renae M, Yernool Dinesh, Shimamoto Keiko, Gouaux Eric
Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168th Street, New York, New York 10032, USA.
Nature. 2007 Jan 25;445(7126):387-93. doi: 10.1038/nature05455. Epub 2007 Jan 17.
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.
次级转运蛋白是整合膜蛋白,通过将底物转运与一个或多个离子梯度偶联来催化底物分子跨脂质双层的移动,从而提供一种底物浓缩摄取机制。本文我们描述了Glt(Ph)的晶体学和热力学研究,Glt(Ph)是一种钠(Na+)偶联的天冬氨酸转运蛋白,确定了天冬氨酸、两个钠离子以及抑制剂d,l-苏式-β-苄氧基天冬氨酸的结合位点。我们进一步表明,螺旋发夹2是细胞外门控,控制底物和离子进入内部结合位点。至少两个钠离子与底物紧密结合,这些钠离子结合位点,与另一种钠偶联转运蛋白LeuT中的钠离子结合位点一起,确定了一个解旋的α-螺旋作为离子结合基序的核心元件,该基序非常适合结合钠离子,并参与转运循环中伴随离子结合和解离的构象变化。