Effect of Peptide Fragment Size on the Propensity of Cyclization in Collision-Induced Dissociation: Oligoglycine b2-b8
Effect of Peptide Fragment Size on the Propensity of Cyclization in Collision-Induced Dissociation: Oligoglycine b2-b8
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DOI：
10.1021/ja9030837
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发表时间：
2009-12-30
影响因子：
15
通讯作者：
Polfer, Nick C.
中科院分区：
文献类型：
--
作者：
Chen, Xian;Yu, Long;Polfer, Nick C.
由于观察到肽片段的氨基酸序列在活化后可以改变，因此目前正在审查通过碰撞诱导解离（CID）的肽片段化的化学。这种重排机制被认为是由于头-尾环化反应，其中片段的N-末端和C-末端部分融合成大环（=环肽）结构，从而"失去"原始序列的记忆。我们对一系列B碎片离子进行了全面的研究，从B（2）到B（8），基于最简单的氨基酸残基甘氨酸，以研究肽链长度对大环碎片结构外观的影响。CID产物离子的结构特征与一系列的气相技术，包括同位素标记，红外光解离光谱，气相氢/氘交换（使用CH3OD），和计算结构的方法。这些结果的综合见解产生了令人信服的证据，即较小的B（n）片段（n = 2，3）仅采用恶唑酮型结构，而对于中等大小的B（n）片段（其中n = 4 - 7），形成恶唑酮和大环B片段结构的混合物。由于这些化学结构中的每一种以不同的速率交换，因此可以使用对H/D交换数据的动力学拟合来近似相对丰度。在这里使用的条件下，"慢"交换大环结构代表B（6）-B（7）的B离子群体的30%，而"快"交换恶唑酮结构代表剩余部分（70%）。有趣的是，对于B（8），仅鉴定了大环结构，这也与HDX结果中的"慢"动力学速率一致。在对照实验中，证实具有6个氨基酸残基的质子化环肽环（Gln-Trp-Phe-Gly-Leu-Met）即使在碰撞活化后也不采用恶唑酮结构。这些结果表明，在某些情况下，较大的大环结构令人惊讶地稳定。虽然需要更多的研究来确定B片段环化的一般倾向，但这项研究的结果在错误序列鉴定方面令人不安。
The chemistry of peptide fragmentation by collision-induced dissociation (CID) is currently being reviewed, as a result of observations that the amino acid sequence of peptide fragments can change upon activation. This rearrangement mechanism is thought to be due to a head-to-tail cyclization reaction, where the N-terminal and C-terminal part of the fragment are fused into a macrocycle (=cyclic peptide) structure, thus "losing" the memory of the original sequence. We present a comprehensive study for a series of b fragment ions, from b(2) to b(8), based on the simplest amino acid residue glycine, to investigate the effect of peptide chain length on the appearance of macrocycle fragment structures. The CID product ions are structurally characterized with a range of gas-phase techniques, including isotope labeling, infrared photodissociation spectroscopy, gas-phase hydrogen/deuterium exchange (using CH3OD), and computational structure approaches. The combined insights from these results yield compelling evidence that smaller b(n) fragments (n = 2, 3) exclusively adopt oxazolone-type structures, whereas a mixture of oxazolone and macrocycle b fragment structures are formed for midsized b(n) fragments, where n = 4-7. As each of these chemical structures exchanges at different rates, it is possible to approximate the relative abundances using kinetic fits to the H/D exchange data. Under the conditions used here, the "slow"-exchanging macrocycle structure represents similar to 30% of the b ion population for b(6)-b(7), while the "fast"-exchanging oxazolone structure represents the remainder (70%). Intriguingly, for b(8) only the macrocycle structure is identified, which is also consistent with the "slow" kinetic rate in the HDX results. In a control experiment, a protonated cyclic peptide with 6 amino acid residues, cyclo(Gln-Trp-Phe-Gly-Leu-Met), is confirmed not to adopt an oxazolone structure, even upon collisional activation. These results demonstrate that in some cases larger macrocycle structures are surprisingly stable. While more studies are required to establish the general propensity for cyclization in b fragments, the implications from this study are troubling in terms of faulty sequence identification.