Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
J Mol Biol. 2013 Nov 15;425(22):4642-51. doi: 10.1016/j.jmb.2013.07.039. Epub 2013 Aug 3.
The quaternary structure of the homodimeric small multidrug resistance protein EmrE has been studied intensely over the past decade. Structural models derived from both two- and three-dimensional crystals show EmrE as an anti-parallel homodimer. However, the resolution of the structures is rather low and their relevance for the in vivo situation has been questioned. Here, we have challenged the available structural models by a comprehensive in vivo Trp scanning of all four transmembrane helices in EmrE. The results are in close agreement with the degree of lipid exposure of individual residues predicted from coarse-grained molecular dynamics simulations of the anti-parallel dimeric structure obtained by X-ray crystallography, strongly suggesting that the X-ray structure provides a good representation of the active in vivo form of EmrE.
过去十年中，同源二聚体小分子多药耐药蛋白 EmrE 的四级结构一直是研究的热点。基于二维和三维晶体的结构模型表明 EmrE 是一个反平行的同源二聚体。然而，这些结构的分辨率相当低，其与体内情况的相关性也受到了质疑。在这里，我们通过对 EmrE 所有四个跨膜螺旋进行全面的体内色氨酸扫描，对现有的结构模型提出了挑战。结果与通过 X 射线晶体学获得的反平行二聚体结构的粗粒度分子动力学模拟预测的单个残基的脂暴露程度非常吻合，强烈表明 X 射线结构提供了 EmrE 活性体内形式的良好表示。
