PDF(Pubmed)
Abstract：
The multidrug efflux transporter EmrE from Escherichia coli requires anionic residues in the substrate binding pocket for coupling drug transport with the proton motive force. Here, we show how protonation of a single membrane embedded glutamate residue (Glu14) within the homodimer of EmrE modulates the structure and dynamics in an allosteric manner using NMR spectroscopy. The structure of EmrE in the Glu14 protonated state displays a partially occluded conformation that is inaccessible for drug binding by the presence of aromatic residues in the binding pocket. Deprotonation of a single Glu14 residue in one monomer induces an equilibrium shift toward the open state by altering its side chain position and that of a nearby tryptophan residue. This structural change promotes an open conformation that facilitates drug binding through a conformational selection mechanism and increases the binding affinity by approximately 2000-fold. The prevalence of proton-coupled exchange in efflux systems suggests a mechanism that may be shared in other antiporters where acid/base chemistry modulates access of drugs to the substrate binding pocket.
摘要：
来自大肠杆菌的多药外排转运蛋白EmrE需要底物结合袋中的阴离子残基，以将药物转运与质子动力偶联。这里,我们展示了EmrE同二聚体中单个膜包埋的谷氨酸残基（Glu14）的质子化如何使用NMR光谱以变构方式调节结构和动力学。处于Glu14质子化状态的EmrE的结构显示出部分封闭的构象,该构象由于在结合袋中存在芳香族残基而无法进行药物结合。一个单体中单个Glu14残基的去质子化通过改变其侧链位置和附近色氨酸残基的位置来诱导向开放状态的平衡移动。这种结构变化促进开放构象,其通过构象选择机制促进药物结合,并使结合亲和力增加约2000倍。质子耦合交换在外排系统中的普遍性表明了一种可能在其他反转运蛋白中共享的机制，其中酸/碱化学调节药物进入底物结合袋。
