Electron capture in spin-trap capped peptides. An experimental example of ergodic dissociation in peptide cation-radicals
Electron capture in spin-trap capped peptides. An experimental example of ergodic dissociation in peptide cation-radicals
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DOI：
10.1016/j.jasms.2006.10.005
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发表时间：
2007-03-01
影响因子：
3.2
通讯作者：
Turecek, Frantisek
中科院分区：
文献类型：
--
作者：
Jones, Jace W.;Sasaki, Tomikazu;Turecek, Frantisek
用在N-末端用2-（4 '-羧基吡啶-2'-基）-4-甲酰胺基团（pepy）封端的十四肽和十五肽研究电子捕获解离，例如，pepy-AEQLLQEEQLLQEL-NH2、pepy-AQEFGEQGQKALKQL-NH2和pepy-AQEGSEQAQKFFKQL-NH2。双重和三重质子化的肽阳离子在离子回旋共振池中进行有效的电子捕获，以产生电荷减少的物质。然而，电子捕获并不伴随着骨架解离。当肽离子通过吸收接近解离阈值的红外光子预热时，随后的电子捕获触发了远端C末端附近的离子解离，主要形成（B（11-14）+ 1）（+中心点）碎片离子，其类似于单独通过红外多光子解离产生的碎片离子。从头计算表明，N-1和N-1'位置的pepy部分的局部气相碱度（GB = 923 kJ mol（-1）），大于那些骨干酰胺基团。因此，pepy可能是双电荷和三电荷离子的质子化位点。质子化的pepy部分中的电子捕获产生电荷减少的阳离子自由基的基态电子态，其具有局部重组能RE = 5.43-5.46 eV，其大于质子化的肽残基。电荷减少的pepy部分中的氢原子结合> 160 kJ mol（-1），这超过了骨架酰胺基团的氢原子亲和力（21-41 kJ mol（-1））。因此，pepy部分作为一个稳定的电子和氢原子陷阱，不触发自由基型解离的肽骨架，这是典型的ECD。相反，通过电子捕获获得的内部能量在肽部分上重新分布，并且当与额外的IR激发结合时，诱导质子驱动的离子解离，其发生在远离电子捕获位点的位点。这个自旋远程碎裂的例子提供了ECD时遍历解离的第一个明确的实验例子。
Electron capture dissociation was studied with tetradecapeptides and pentadecapeptides that were capped at N-termini with a 2-(4'-carboxypyrid-2'-yl)-4-carboxamide group (pepy), e.g., pepy-AEQLLQEEQLLQEL-NH2, pepy-AQEFGEQGQKALKQL-NH2, and pepy-AQEGSEQAQKFFKQL-NH2. Doubly and triply protonated peptide cations underwent efficient electron capture in the ion-cyclotron resonance cell to yield charge-reduced species. However, the electron capture was not accompanied by backbone dissociations. When the peptide ions were preheated by absorption of infrared photons close to the dissociation threshold, subsequent electron capture triggered ion dissociations near the remote C-terminus forming mainly (b(11-14) + 1)(+center dot) fragment ions that were analogous to those produced by infrared multiphoton dissociation alone. Ab initio calculations indicated that the N-1 and N-1' positions in the pepy moiety had topical gas-phase basicities (GB = 923 kJ mol(-1)) that were greater than those of backbone amide groups. Hence, pepy was a likely protonation site in the doubly and triply charged ions. Electron capture in the protonated pepy moiety produced the ground electronic state of the charge-reduced cation-radical with a topical recombination energy, RE = 5.43-5.46 eV, which was greater than that of protonated peptide residues. The hydrogen atom in the charge-reduced pepy moiety was bound by > 160 kJ mol(-1), which exceeded the hydrogen atom affinity of the backbone amide groups (21-41 kJ mol(-1)). Thus, the pepy moiety functioned as a stable electron and hydrogen atom trap that did not trigger radical-type dissociations in the peptide backbone that are typical of ECD. Instead, the internal energy gained by electron capture was redistributed over the peptide moiety, and when combined with additional IR excitation, induced proton-driven ion dissociations which occurred at sites that, were remote from the site of electron capture. This example of a spin-remote fragmentation provided the first clear-cut experimental example of an ergodic dissociation upon ECD.