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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Energetics and Dynamics of the Fragmentation Reactions of Protonated Peptides Containing Methionine Sulfoxide or Aspartic Acid via Energy- and Time-Resolved Surface Induced Dissociation
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Energetics and Dynamics of the Fragmentation Reactions of Protonated Peptides Containing Methionine Sulfoxide or Aspartic Acid via Energy- and Time-Resolved Surface Induced Dissociation

机译：通过能量和时间分辨的表面诱导离解，含有蛋氨酸亚砜或天冬氨酸的质子化肽的片段化反应的能量和动力学

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The surface-induced dissociation (SID) of six model peptides containing either methionine sulfoxide or aspartic acid (GAILM(O)GAILR, GAILM(O)GAILK, GAILM(O)GAILA, GAILDGAILR, GAILDGAILK, and GAILDGAILA) have been studied using a specially configured Fourier transform ion-cyclotron resonance mass spectrometer (FT-ICR MS). In particular, we have investigated the energetics and dynamics associated with (i) preferential cleavage of the methionine sulfoxide side chain via the loss of GH3SOH (64 Da), and (ii) preferential cleavage of the amide bond C-terminal to aspartic acid. The role of proton mobility in these selective bond cleavage reactions was examined by changing the C-terminal residue of the peptide from arginine (nonmobile proton conditions) to lysine (partially mobile proton conditions) to alanine (mobile proton conditions). Time- and energy-resolved fragmentation efficiency curves (TFECs) reveal that selective cleavages due to the methionine sulfoxide and aspartic acid residues are characterized by slow fragmentation kinetics. RRKM modeling of the experimental data suggests that the slow kinetics is associated with large negative entropy effects and these may be due to the presence of rearrangements prior to fragmentation. It was found that the Arrhenius pre-exponential factor (A) for peptide fragmentations occurring via selective bond cleavages are 1-2 orders of magnitude lower than nonselective peptide fragmentation reactions, while the dissociation threshold (E_0) is relatively invariant. This means that selective bond cleavage is kinetically disfavored compared to nonselective amide bond cleavage. It was also found that the energetics and dynamics for the preferential loss of CH3SOH from peptide ions containing methionine sulfoxide are very similar to selective C-terminal amide bond cleavage at the aspartic acid residue. These results suggest that while preferential cleavage can compete with amide bond cleavage energetically, dynamically, these processes are much slower compared to amide bond cleavage, explaining why these selective bond cleavages are not observed if fragmentation is performed under mobile proton conditions. This study further affirms that fragmentation of peptide ions in the gas phase are predominantly governed by entropic effects.
机译：已使用A研究了包含蛋氨酸亚砜或天冬氨酸的六个模型肽（GAILM（O）GAILR，GAILM（O）GAILK，GAILM（O）GAILA，GAILDGAILR，GAILDGAILK和GAILDGAILA）的表面诱导解离（SID）专门配置的傅里叶变换离子回旋共振质谱仪（FT-ICR MS）。特别是，我们研究了与（i）通过丢失GH3SOH（64 Da）优先切割甲硫氨酸亚砜侧链和（ii）将天冬氨酸的C端酰胺键优先裂解有关的能量和动力学。通过将肽的C末端残基从精氨酸（非移动质子条件）变为赖氨酸（部分移动质子条件）到丙氨酸（移动质子条件）来检查质子迁移在这些选择性键裂解反应中的作用。时间和能量分辨的碎裂效率曲线（TFEC）表明，由于甲硫氨酸亚砜和天冬氨酸残基引起的选择性裂解具有缓慢的碎裂动力学特性。 RRKM对实验数据的建模表明，缓慢的动力学与大的负熵效应有关，这可能是由于碎片之前存在重排。发现通过选择性键断裂发生的肽片段断裂的Arrhenius指数前因子（A）比非选择性肽片段断裂反应低1-2个数量级，而解离阈值（E_0）相对不变。这意味着与非选择性酰胺键裂解相比，选择性键裂解在动力学上是不利的。还发现，从含有蛋氨酸亚砜的肽离子中优先损失CH3SOH的能量和动力学与天冬氨酸残基的选择性C末端酰胺键裂解非常相似。这些结果表明，虽然优先裂解可以动态地与酰胺键裂解竞争，但是与酰胺键裂解相比，这些过程要慢得多，这解释了如果在移动质子条件下进行断裂，为什么没有观察到这些选择性键裂解。这项研究进一步证实，气相中肽离子的断裂主要受熵的影响。

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