Native Ion Mobility Mass Spectrometry: When Gas-Phase Ion Structures Depend on the Electrospray Charging Process
Native Ion Mobility Mass Spectrometry: When Gas-Phase Ion Structures Depend on the Electrospray Charging Process
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DOI：
10.1007/s13361-019-02152-3
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发表时间：
2019-06-01
影响因子：
3.2
通讯作者：
Gabelica, Valerie
中科院分区：
文献类型：
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作者：
Khristenko, Nina;Amato, Jussara;Gabelica, Valerie
离子迁移谱（IMS）已成为表征生物分子折叠的流行方法。许多研究表明，在溶液中折叠的蛋白质在气相中保持折叠，而在溶液中未折叠的蛋白质在气相中采用更扩展的构象。在这里，我们讨论一下这个原则有多普遍。我们研究了单链DNA（具有CCCTAA重复的人类端粒胞嘧啶富集序列），由于C-H+-C碱基对的形成，其以pH依赖的方式折叠成插入基序（i-motif）结构。由于i-基序形成在低离子强度下是有利的，我们可以研究在pH 5.5下在宽范围的乙酸铵浓度（15至100 mM）下i-基序结构的ESI-IMS-MS行为。对照实验由pH 7.5下的相同序列（其中序列未折叠）或不能形成i-基序的序列变体（CTCTAA重复）组成。令人惊讶的结果来自对照实验。我们发现，溶液的离子强度对气相结构的致密性有更大的影响比溶液折叠状态。这意味着电喷雾离子保持充电过程的记忆，这受到电解质浓度的影响。我们讨论了这些结果在光的分析物之间的液滴内部和液滴表面，这反过来又影响被电离通过带电的残留物型途径或链挤出型途径的概率分区。
Ion mobility spectrometry (IMS) has become popular to characterize biomolecule folding. Numerous studies have shown that proteins that are folded in solution remain folded in the gas phase, whereas proteins that are unfolded in solution adopt more extended conformations in the gas phase. Here, we discuss how general this tenet is. We studied single-stranded DNAs (human telomeric cytosine-rich sequences with CCCTAA repeats), which fold into an intercalated motif (i-motif) structure in a pH-dependent manner, thanks to the formation of C-H+-C base pairs. As i-motif formation is favored at low ionic strength, we could investigate the ESI-IMS-MS behavior of i-motif structures at pH 5.5 over a wide range of ammonium acetate concentrations (15 to 100mM). The control experiments consisted of either the same sequence at pH 7.5, wherein the sequence is unfolded, or sequence variants that cannot form i-motifs (CTCTAA repeats). The surprising results came from the control experiments. We found that the ionic strength of the solution had a greater effect on the compactness of the gas-phase structures than the solution folding state. This means that electrosprayed ions keep a memory of the charging process, which is influenced by the electrolyte concentration. We discuss these results in light of the analyte partitioning between the droplet interior and the droplet surface, which in turn influences the probability of being ionized via a charged residue-type pathway or a chain extrusion-type pathway.