Quasi-symmetry in the cryo-EM structure of EmrE provides the key to modeling its transmembrane domain
Quasi-symmetry in the cryo-EM structure of EmrE provides the key to modeling its transmembrane domain
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DOI：
10.1016/j.jmb.2006.08.072
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发表时间：
2006-11-17
影响因子：
5.6
通讯作者：
Ben-Tal, Nir
中科院分区：
文献类型：
--
作者：
Fleishman, Sarel J.;Harrington, Susan E.;Ben-Tal, Nir
小的多药耐药性（SMR）转运蛋白有助于细菌耐药性耦合流出的广泛的有毒芳香族阳离子，其中一些是常用的抗生素和防腐剂，质子流入。EmrE是一种原型的小的多药耐药转运蛋白，包含形成二聚体的四个跨膜片段（M1-M4）。最近有人提出，EmrE分子在二聚体中具有不同的拓扑结构，即单体相对于膜平面具有相反的取向。通过电子冷冻显微镜（cryo-EM）在膜平面中以7.5埃的分辨率获得的EmrE的3-D结构表明，部分结构与准对称性相关。我们使用这种对称关系，结合序列保守性数据，将EmrE中的跨膜片段分配给cryo-EM结构中看到的密度。通过考虑每个螺旋的进化保守模式，构建了跨膜区的C-alpha模型。该模型被验证的EmrE与大多数的位置，被确定为影响基板易位位于周围的基板结合腔的生化数据。在小的多药耐药反向转运蛋白中质子偶联底物易位的建议机制为实验观察到的倒置拓扑结构提供了一个机械原理。(c)2006爱思唯尔有限公司保留所有权利。
Small multidrug resistance (SMR) transporters contribute to bacterial resistance by coupling the efflux of a wide range of toxic aromatic cations, some of which are commonly used as antibiotics and antiseptics, to proton influx. EmrE is a prototypical small multidrug resistance transporter comprising four transmembrane segments (M1-M4) that forms dimers. It was suggested recently that EmrE molecules in the dimer have different topologies, i.e. monomers have opposite orientations with respect to the membrane plane. A 3-D structure of EmrE acquired by electron cryo-microscopy (cryo-EM) at 7.5 angstrom resolution in the membrane plane showed that parts of the structure are related by quasi-symmetry. We used this symmetry relationship, combined with sequence conservation data, to assign the transmembrane segments in EmrE to the densities seen in the cryo-EM structure. A C-alpha model of the transmembrane region was constructed by considering the evolutionary conservation pattern of each helix. The model is validated by much of the biochemical data on EmrE with most of the positions that were identified as affecting substrate translocation being located around the substrate-binding cavity. A suggested mechanism for proton-coupled substrate translocation in small multidrug resistance antiporters provides a mechanistic rationale to the experimentally observed inverted topology. (c) 2006 Elsevier Ltd. All rights reserved.