Native electrospray mass spectrometry is a powerful method for determining the native stoichiometry of many polydisperse multi-subunit biological complexes, including multi-subunit protein complexes and lipid-bound transmembrane proteins. However, when polydispersity results from incorporation of multiple copies of two or more different subunits, it can be difficult to analyze subunit stoichiometry using conventional mass spectrometry analysis methods, especially when m/z distributions for different charge states overlap in the mass spectrum. It was recently demonstrated by Marty and co-workers (K. K. Hoi, et al., Anal. Chem., 2016, 88, 6199–6204) that Fourier Transform (FT)-based methods can determine the bulk average lipid composition of protein-lipid Nanodiscs assembled with two different lipids, but a detailed statistical description of the composition of more general polydisperse two-subunit populations is still difficult to achieve. This results from the vast number of ways in which the two types of subunit can be distributed within the analyte ensemble. Here, we present a theoretical description of three common classes of heterogeneity for mixed-subunit analytes and demonstrate how to differentiate and analyze them using mass spectrometry and FT methods. First, we first describe FT-based analysis of mass spectra corresponding to simple superpositions, convolutions, and multinomial distributions for two or more different subunit types using model data sets. We then apply these principles with real samples, including mixtures of single-lipid Nanodiscs in the same solution (superposition), mixed-lipid Nanodiscs and copolymers (convolutions), and isotope distribution for ubiquitin (multinomial distribution). This classification scheme and the FT method used to study these analyte classes should be broadly useful in mass spectrometry as well as other techniques where overlapping, periodic signals arising from analyte mixtures are common.

中文翻译：

---

不同类别的多亚基异质性：使用傅立叶变换方法和原生质谱法进行分析。

天然电喷雾质谱法是确定许多多分散多亚基生物复合物（包括多亚基蛋白质复合物和脂质结合跨膜蛋白）的天然化学计量的有效方法。然而，当多分散性是由两个或多个不同亚基的多个拷贝的结合导致时，使用传统的质谱分析方法可能难以分析亚基化学计量，尤其是当不同电荷状态的m / z分布在质谱中重叠时。Marty 及其同事最近证明了这一点 (KK Hoi, et al. , Anal. Chem. , 2016, 88, 6199–6204) 基于傅立叶变换 (FT) 的方法可以确定由两种不同脂质组装的蛋白质脂质纳米圆盘的整体平均脂质组成，但对更一般的多分散二亚基群体的组成的详细统计描述仍然是难以实现。这是由于两种类型的亚基可以在分析物集合中分布的大量方式造成的。在这里，我们对混合亚基分析物的三类常见异质性进行了理论描述，并演示了如何使用质谱法和 FT 方法区分和分析它们。首先，我们首先描述了基于 FT 的质谱分析，这些质谱对应于使用模型数据集的两个或多个不同亚基类型的简单叠加、卷积和多项式分布。然后，我们将这些原理应用于真实样品，包括同一溶液中单脂质纳米圆盘的混合物（叠加）、混合脂质纳米圆盘和共聚物（卷积）以及泛素的同位素分布（多项分布）。这种分类方案和用于研究这些分析物类别的 FT 方法应该广泛用于质谱以及其他技术，在这些技术中，由分析物混合物产生的重叠周期性信号很常见。