Topologically Random Insertion of EmrE Supports a Pathway for Evolution of Inverted Repeats in Ion-coupled Transporters
Topologically Random Insertion of EmrE Supports a Pathway for Evolution of Inverted Repeats in Ion-coupled Transporters
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DOI：
10.1074/jbc.m110.108746
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发表时间：
2010-05-14
影响因子：
4.8
通讯作者：
Schuldiner, Shimon
中科院分区：
文献类型：
--
作者：
Nasie, Iris;Steiner-Mordoch, Sonia;Schuldiner, Shimon
离子偶联转运蛋白中的反向重复序列在许多不相关的家族中独立进化。有人认为，这种倒置对称性是转运蛋白构象转变机制的基本要素。我们在这里表明，小的多药物转运蛋白提供了一个模型，这种重复的演变。该家族包括同源二聚体和密切相关的异源二聚体。在前者中，每个原聚体中明显相同的拓扑决定因素很弱，我们表明，对于EmrE（来自大肠杆菌的同二聚体），插入膜是随机的，并且无论它们是否插入细胞质，二聚体都是有功能的。N-和C-末端结构域面向细胞内部或外部。此外，被设计为插入具有偏置拓扑结构的突变体是功能性的，而不管拓扑结构如何。在EbrAB的情况下，异二聚体同源物应该相互作用的反平行，我们表明，亚基之一，EbrB，也可以作为一个同源二聚体，最有可能在一个平行的模式。此外，EmrE同源二聚体可以通过融合额外的跨膜区段而被迫形成反平行拓扑结构。耦合离子和底物运输的机制的简单性和对底物识别的几个要求提供了耐受在亚基的相互作用和相对于膜的二聚体拓扑结构中的这种独特的和前所未有的模糊性所必需的鲁棒性。结果表明，小的多药物转运蛋白是在一个进化的交界处，并提供了一个模型的结构演变的转运蛋白。
Inverted repeats in ion-coupled transporters have evolved independently in many unrelated families. It has been suggested that this inverted symmetry is an essential element of the mechanism that allows for the conformational transitions in transporters. We show here that small multidrug transporters offer a model for the evolution of such repeats. This family includes both homodimers and closely related heterodimers. In the former, the topology determinants, evidently identical in each protomer, are weak, and we show that for EmrE, an homodimer from Escherichia coli, the insertion into the membrane is random, and dimers are functional whether they insert into the cytoplasmic membrane with the N- and C-terminal domains facing the inside or the outside of the cell. Also, mutants designed to insert with biased topology are functional regardless of the topology. In the case of EbrAB, a heterodimer homologue supposed to interact antiparallel, we show that one of the subunits, EbrB, can also function as a homodimer, most likely in a parallel mode. In addition, the EmrE homodimer can be forced to an antiparallel topology by fusion of an additional transmembrane segment. The simplicity of the mechanism of coupling ion and substrate transport and the few requirements for substrate recognition provide the robustness necessary to tolerate such a unique and unprecedented ambiguity in the interaction of the subunits and in the dimer topology relative to the membrane. The results suggest that the small multidrug transporters are at an evolutionary junction and provide a model for the evolution of structure of transport proteins.