Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0307, United States.
J Am Chem Soc. 2013 Jun 26;135(25):9299-302. doi: 10.1021/ja4042115. Epub 2013 Jun 17.
The three-dimensional structure of the 81-residue mercury transporter MerF determined in liquid crystalline phospholipid bilayers under physiological conditions by Rotationally Aligned (RA) solid-state NMR has two long helices, which extend well beyond the bilayer, with a well-defined interhelical loop. Truncation of the N-terminal 12 residues, which are mobile and unstructured when the protein is solubilized in micelles, results in a large structural rearrangement of the protein in bilayers. In the full-length protein, the N-terminal helix is aligned nearly parallel to the membrane normal and forms an extension of the first transmembrane helix. By contrast, this helix adopts a perpendicular orientation in the truncated protein. The close spatial proximity of the two Cys-containing metal binding sites in the three-dimensional structure of full-length MerF provides insights into possible transport mechanisms. These results demonstrate that major changes in protein structure can result from differences in amino acid sequence (e.g., full-length vs truncated proteins) as well as the use of a non-native membrane mimetic environment (e.g., micelles) vs liquid crystalline phospholipid bilayers. They provide further evidence of the importance of studying unmodified membrane proteins in near-native bilayer environments in order to obtain accurate structures that can be related to their functions.
在生理条件下，通过旋转排列（RA）固态 NMR 在液晶磷脂双层中测定的 81 个残基的汞转运蛋白 MerF 的三维结构具有两个长螺旋，这些螺旋远远超出双层，具有明确的螺旋间环。截断 N 端的 12 个残基，当蛋白质在胶束中溶解时，这些残基是移动的且无结构的，导致蛋白质在双层中的结构发生大的重排。在全长蛋白质中，N 端螺旋几乎与膜法线平行排列，并形成第一个跨膜螺旋的延伸。相比之下，在截断的蛋白质中，该螺旋采用垂直取向。三维结构中两个含半胱氨酸的金属结合位点的紧密空间接近提供了对可能的运输机制的深入了解。这些结果表明，蛋白质结构的主要变化可能来自于氨基酸序列的差异（例如，全长与截断蛋白）以及非天然膜模拟环境（例如胶束）与液晶磷脂双层的使用。它们进一步证明了在接近天然双层环境中研究未修饰的膜蛋白以获得可与其功能相关的准确结构的重要性。
