Electron transfer dissociation (ETD) has attracted increasing interest due to its complementarity to collision-induced dissociation (CID). ETD allows the direct localization of labile post-translational modifications, which is of main interest in proteomics where differences and similarities between ETD and CID have been widely studied. However, due to the fact that ETD requires precursor ions to carry at least two charges, little is known about differences in ETD and CID of small molecules such as metabolites. In this work, ETD and CID of desmosine (DES) and isodesmosine (IDS), two isomers that due to the presence of a pyridinium group can carry two charges after protonation, are studied and compared. In addition, the influence of DES/IDS derivatization with propionic anhydride and polyethyleneglycol (PEG) reagents on ETD and CID was studied, since this is a common strategy to increase sensitivity and to facilitate the analysis by reversed-phase chromatography. Clear differences between ETD and CID of non-derivatized and derivatized-DES/IDS were observed. While CID is mainly attributable to charge-directed fragmentation, ETD is initiated by the generation of a hydrogen atom at the initial protonation site and its subsequent transfer to the pyridinium ring of DES/IDS. These differences are reflected in the generation of complex CID spectra dominated by the loss of small, noninformative molecules (NH3, CO, H2O), while ETD spectra are simpler and dominated by characteristic side-chain losses. This constitutes a potential advantage of ETD in comparison to CID when employed for the targeted analysis of DES/IDS in biological samples.
电子转移解离(ETD)因其与碰撞诱导解离(CID)的互补性而受到越来越多的关注。电子转移解离可直接定位易变的翻译后修饰,这也是蛋白质组学的主要兴趣所在,ETD 和 CID 之间的异同已被广泛研究。然而,由于 ETD 要求前体离子至少带两个电荷,因此人们对代谢物等小分子的 ETD 和 CID 的差异知之甚少。在这项工作中,研究并比较了去甲
肌苷(DES)和异去甲
肌苷(IDS)的 ETD 和 CID,这两种异构体由于存在一个
吡啶基,质子化后可携带两种电荷。此外,还研究了用
丙酸酐和聚
乙二醇(P
EG)试剂衍生 DES/IDS 对 ETD 和 CID 的影响,因为这是提高灵敏度和方便反相
色谱分析的常用策略。观察到未衍生化和衍生化 DES/IDS 的 ETD 和 CID 之间存在明显差异。CID 主要归因于电荷定向碎片,而 ETD 则是由初始质子化位点产生的氢原子及其随后转移到 DES/IDS 的
吡啶鎓环上引起的。这些差异反映在产生复杂的 CID 图谱上,主要是损失了小的、无信息的分子(NH3、CO、
H2O),而 ETD 图谱较为简单,主要是损失了特征性侧链。这也是 ETD 与 CID 相比在
生物样本中定向分析 DES/IDS 时的潜在优势。