Effects of Polarity on the Structures and Charge States of Native-Like Proteins and Protein Complexes in the Gas Phase
Effects of Polarity on the Structures and Charge States of Native-Like Proteins and Protein Complexes in the Gas Phase
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DOI：
10.1021/ac403139d
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发表时间：
2013-12-17
影响因子：
7.4
通讯作者：
Bush, Matthew F.
中科院分区：
文献类型：
--
作者：
Allen, Samuel J.;Schwartz, Alicia M.;Bush, Matthew F.
使用天然质谱和离子迁移谱来研究质量范围为 6 至 468 kDa 的蛋白质和蛋白质复合物的选定阳离子和阴离子的气相结构。在相同的溶液条件下，观察到的所有类天然阴离子的平均电荷态均小于相应阳离子的平均电荷态。使用射频限制漂移池，在正离子和负离子模式下测量了相似的碰撞截面，表明阴离子和阳离子具有非常相似的结构。该结果表明，对于该质量范围内的蛋白质和蛋白质复合离子，选择特定极性来捕获更接近天然的结构并没有固有的好处。对于肽和低质量蛋白质，极性和电荷状态依赖的结构变化可能更显着。带电残基模型最常用于解释基于瑞利极限的大分子电离，瑞利极限定义了液滴可以容纳的电荷上限。由于两种极性的离子具有相似的结构，并且瑞利极限不依赖于极性，因此这些结果不能仅用带电残基模型来解释。相反，观察到的电荷态分布与分析物去溶剂化最后阶段的电荷载流子发射最为一致，阴离子的电荷载流子发射能量低于相应的阳离子。这些结果表明，在大多数本机质谱实验中观察到的电荷态分布是由电荷载流子发射过程决定的。尽管瑞利极限可以确定较大物种（例如病毒衣壳）的气相电荷状态。
Native mass spectrometry and ion mobility spectrometry were used to investigate the gas-phase structures of selected cations and anions of proteins and protein complexes with masses ranging from 6 to 468 kDa. Under the same solution conditions, the average charge states observed for all native-like anions were less than those for the corresponding cations. Using an rf-confining drift cell, similar collision cross sections were measured in positive and negative ion mode suggesting that anions and cations have very similar structures. This result suggests that for protein and protein complex ions within this mass range, there is no inherent benefit to selecting a specific polarity for capturing a more native-like structure. For peptides and low-mass proteins, polarity and charge-state dependent structural changes may be more significant. The charged-residue model is most often used to explain the ionization of large macromolecules based on the Rayleigh limit, which defines the upper limit of charge that a droplet can hold. Because ions of both polarities have similar structures and the Rayleigh limit does not depend on polarity, these results cannot be explained by the charged-residue model alone. Rather, the observed charge-state distributions are most consistent with charge-carrier emissions during the final stages of analyte desolvation, with lower charge-carrier emission energies for anions than the corresponding cations. These results suggest that the observed charge-state distributions in most native mass spectrometry experiments are determined by charge-carrier emission processes; although the Rayleigh limit may determine the gas-phase charge states of larger species, e.g., virus capsids.