Bavarian NMR Center at the Department of Chemistry, Technical University of Munich, Ernst-Otto-Fischer-Str. 2, 85747 Garching, Germany; Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany.
Bavarian NMR Center at the Department of Chemistry, Technical University of Munich, Ernst-Otto-Fischer-Str. 2, 85747 Garching, Germany; Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany.
Prog Nucl Magn Reson Spectrosc. 2019 Oct-Dec;114-115:271-283. doi: 10.1016/j.pnmrs.2019.08.001. Epub 2019 Aug 26.
Membrane proteins are important players in signal transduction and the exchange of metabolites within or between cells. Thus, this protein class is the target of around 60 % of currently marketed drugs, emphasizing their essential biological role. Besides functional assays, structural and dynamical investigations on this protein class are crucial to fully understanding their functionality. Even though X-ray crystallography and electron microscopy are the main methods to determine structures of membrane proteins and their complexes, NMR spectroscopy can contribute essential information on systems that (a) do not crystallize and (b) are too small for EM. Furthermore, NMR is a versatile tool for monitoring functional dynamics of biomolecules at various time scales. A crucial aspect of such studies is the use of a membrane mimetic that resembles a native environment and thus enables the extraction of functional insights. In recent decades, the membrane protein NMR community has moved from rather harsh detergents to membrane systems having more native-like properties. In particular, most recently phospholipid nanodiscs have been developed and optimized mainly for solution-state NMR but are now also being used for solid-state NMR spectroscopy. Nanodiscs consist of a patch of a planar lipid bilayer that is encircled by different (bio-)polymers to form particles of defined and tunable size. In this review, we provide an overview of available membrane mimetics, including nanodiscs, amphipols and bicelles, that are suitable for high-resolution NMR spectroscopy and describe how these advanced membrane mimetics can facilitate NMR studies on the structure and dynamics of membrane proteins. Since the stability of membrane proteins depends critically on the chosen membrane mimetic, we emphasize the importance of a suitable system that is not necessarily developed for solution-state NMR applications and hence requires optimization for each membrane protein. However, lipid-based membrane mimetics offer the possibility of performing NMR experiments at elevated temperatures and studying ligand and partner protein complexes as well as their functional dynamics in a realistic membrane environment. In order to be able to make an informed decision during the selection of a suitable membrane system, we provide a detailed overview of the available options for various membrane protein classes and thereby facilitate this often-difficult selection process for a broad range of desired NMR applications.
膜蛋白是信号转导和细胞内外代谢物交换的重要参与者。因此，这类蛋白质是目前市场上约 60%的药物的靶点，这强调了它们在生物学上的重要作用。除了功能测定外，对这类蛋白质的结构和动力学研究对于充分了解其功能至关重要。尽管 X 射线晶体学和电子显微镜是确定膜蛋白及其复合物结构的主要方法，但 NMR 光谱学可以为（a）不结晶和（b）太小而不适合 EM 的系统提供重要信息。此外，NMR 是一种用于监测各种时间尺度下生物分子功能动力学的多功能工具。此类研究的一个关键方面是使用类似于天然环境的膜模拟物，从而可以提取功能见解。在过去的几十年中，膜蛋白 NMR 界已经从相当苛刻的去污剂转向具有更类似天然特性的膜系统。特别是，最近已经开发和优化了磷脂纳米盘，主要用于溶液状态 NMR，但现在也用于固态 NMR 光谱学。纳米盘由一个平面脂质双层的斑块组成，该斑块被不同的（生物）聚合物包围，形成具有确定和可调尺寸的颗粒。在这篇综述中，我们提供了可用的膜模拟物的概述，包括纳米盘、两性聚合物和双分子层脂囊泡，这些模拟物适合高分辨率 NMR 光谱学，并描述了这些先进的膜模拟物如何促进膜蛋白结构和动力学的 NMR 研究。由于膜蛋白的稳定性取决于所选择的膜模拟物，因此我们强调了选择一个不一定为溶液状态 NMR 应用开发的合适系统的重要性，因此需要针对每个膜蛋白进行优化。然而，基于脂质的膜模拟物提供了在升高温度下进行 NMR 实验以及在真实膜环境中研究配体和伴侣蛋白复合物及其功能动力学的可能性。为了能够在选择合适的膜系统时做出明智的决定，我们详细概述了各种膜蛋白类别的可用选项，从而为广泛的所需 NMR 应用的这一通常困难的选择过程提供了便利。
