Swaney Danielle L, McAlister Graeme C, Wirtala Matthew, Schwartz Jae C, Syka John E P, Coon Joshua J
Departments of Chemistry and Biomolecular Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
Anal Chem. 2007 Jan 15;79(2):477-85. doi: 10.1021/ac061457f.
Electron-transfer dissociation (ETD) delivers the unique attributes of electron capture dissociation to mass spectrometers that utilize radio frequency trapping-type devices (e.g., quadrupole ion traps). The method has generated significant interest because of its compatibility with chromatography and its ability to: (1) preserve traditionally labile post-translational modifications (PTMs) and (2) randomly cleave the backbone bonds of highly charged peptide and protein precursor ions. ETD, however, has shown limited applicability to doubly protonated peptide precursors, [M + 2H]2+, the charge and type of peptide most frequently encountered in "bottom-up" proteomics. Here we describe a supplemental collisional activation (CAD) method that targets the nondissociated (intact) electron-transfer (ET) product species ([M + 2H]+) to improve ETD efficiency for doubly protonated peptides (ETcaD). A systematic study of supplementary activation conditions revealed that low-energy CAD of the ET product population leads to the near-exclusive generation of c- and z-type fragment ions with relatively high efficiency (77 +/- 8%). Compared to those formed directly via ETD, the fragment ions were found to comprise increased relative amounts of the odd-electron c-type ions (c+) and the even-electron z-type ions (z+). A large-scale analysis of 755 doubly charged tryptic peptides was conducted to compare the method (ETcaD) to ion trap CAD and ETD. ETcaD produced a median sequence coverage of 89%-a significant improvement over ETD (63%) and ion trap CAD (77%).
电子转移解离（ETD）将电子捕获解离的独特特性引入到使用射频阱式装置（如四极杆离子阱）的质谱仪中。该方法因其与色谱的兼容性以及具备以下能力而引发了广泛关注：（1）保留传统上不稳定的翻译后修饰（PTM）；（2）随机裂解高电荷肽和蛋白质前体离子的主链键。然而，ETD对双质子化肽前体[M + 2H]²⁺的适用性有限，而[M + 2H]²⁺是“自下而上”蛋白质组学中最常遇到的肽电荷和类型。在此，我们描述了一种补充性碰撞激活（CAD）方法，该方法针对未解离的（完整的）电子转移（ET）产物物种（[M + 2H]⁺），以提高双质子化肽的ETD效率（ETcaD）。对补充激活条件的系统研究表明，ET产物群体的低能量CAD导致以相对较高的效率（77±8%）几乎排他性地生成c型和z型碎片离子。与直接通过ETD形成的碎片离子相比，发现这些碎片离子包含相对含量增加的奇电子c型离子（c⁺）和偶电子z型离子（z⁺）。对755个双电荷胰蛋白酶肽进行了大规模分析，以将该方法（ETcaD）与离子阱CAD和ETD进行比较。ETcaD产生的中位序列覆盖率为89%，相较于ETD（63%）和离子阱CAD（77%）有显著提高。
