Membrane proteins are traditionally extracted and purified in detergent for biochemical and structural characterisation. This process is often costly and laborious, and the stripping away of potentially stabilising lipids from the membrane protein of interest can have detrimental effects on protein integrity. Recently, styrene-maleic acid (SMA) co-polymers have offered a solution to this problem by extracting membrane proteins directly from their native membrane, while retaining their naturally associated lipids in the form of stable SMA lipid particles (SMALPs). However, the inherent nature and heterogeneity of the polymer renders their use challenging for some downstream applications - particularly mass spectrometry (MS). While advances in cryo-electron microscopy (cryo-EM) have enhanced our understanding of membrane protein:lipid interactions in both SMALPs and detergent, the resolution obtained with this technique is often insufficient to accurately identify closely associated lipids within the transmembrane annulus. Native-MS has the power to fill this knowledge gap, but the SMA polymer itself remains largely incompatible with this technique. To increase sample homogeneity and allow characterisation of membrane protein:lipid complexes by native-MS, we have developed a novel SMA-exchange method; whereby the membrane protein of interest is first solubilised and purified in SMA, then transferred into amphipols or detergents. This allows the membrane protein and endogenously associated lipids extracted by SMA co-polymer to be identified and examined by MS, thereby complementing results obtained by cryo-EM and creating a better understanding of how the lipid bilayer directly affects membrane protein structure and function.

中文翻译：

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苯乙烯马来酸脂质颗粒（SMALPs）进入去污剂或两栖动物：膜蛋白表征的交换协议。

传统上，膜蛋白是在去污剂中提取和纯化的，用于生物化学和结构表征。该过程通常是昂贵且费力的，并且从感兴趣的膜蛋白中剥离可能稳定的脂质可能会对蛋白完整性产生不利影响。最近，苯乙烯-马来酸（SMA）共聚物通过直接从其天然膜中提取膜蛋白，同时以稳定的SMA脂质颗粒（SMALP）形式保留其天然缔合的脂质，从而为该问题提供了解决方案。但是，聚合物的固有性质和异质性使其在某些下游应用（尤其是质谱分析（MS））中的使用面临挑战。尽管低温电子显微镜（cryo-EM）的进步增强了我们对膜蛋白的了解：SMALPs和去污剂中的脂质相互作用，用这种技术获得的分辨率通常不足以准确地识别跨膜瓣环内紧密相关的脂质。Native-MS可以弥补这一知识空白，但是SMA聚合物本身仍然与该技术不兼容。为了提高样品的均一性并通过天然MS表征膜蛋白：脂质复合物，我们开发了一种新颖的SMA交换方法；从而将感兴趣的膜蛋白首先在SMA中溶解和纯化，然后转移到两性动物或去污剂中。这样可以通过SMA共聚物鉴定并检查通过SMA共聚物提取的膜蛋白和内源性相关脂质，