Deamidation: Differentiation of aspartyl from isoaspartyl products in peptides by electron capture dissociation
Deamidation: Differentiation of aspartyl from isoaspartyl products in peptides by electron capture dissociation
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DOI：
10.1110/ps.041062905
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发表时间：
2005-02-01
期刊：
影响因子：
8
通讯作者：
O'Connor, PB
中科院分区：
文献类型：
--
作者：
Cournoyer, JJ;Pittman, JL;O'Connor, PB
蛋白质中天冬酰胺基的脱酰胺和天冬酰胺基残基的异构化通过琥珀酰亚胺中间体进行，产生天冬酰胺基和异天冬酰胺基残基的混合物。异天冬氨酸是天冬氨酸的异构体，其中C-β并入主链中，从而使蛋白质主链的长度增加一个亚甲基单元。这种翻译后修饰被怀疑有助于蛋白质的老化和蛋白质折叠障碍，如阿尔茨海默病，因此区分两种异构体变得重要。本文报道了用傅里叶变换质谱仪（FTMS）通过电子捕获解离（ECD）来区分肽中的异戊酰基残基。对具有异戊酰基残基的模型肽及其异戊酰基类似物进行了检查，并且发现对应于C-n（.）+的独特峰。58和z（θ-n）-57碎片离子（n，Asp的位置; E，肽中氨基酸的总数）仅在具有异丙基残基的肽的光谱中发现。提出的断裂机制涉及C.- C骨架键，因此在两个片段之间分裂isoasZ partyl残基。此外，观察到的对乙酰基残基特异性的互补特征是来自电荷减少物质的天冬氨酸侧链的中性损失。来自相同仪器的肽的CAD光谱证明了改进的方法，因为先前公布的CAD方法依赖于与具有乙酰基残基的标准品的光谱的比较。潜在的使用自上而下的方法来检测和解决产品的天冬酰胺基和异构化的乙酰基残基进行了讨论。
Deamidation of asparaginyl and isomerization of aspartyl residues in proteins proceed through a succinimide intermediate producing a mixture of aspartyl and isoaspartyl residues. Isoaspartic acid is an isomer of aspartic acid with the C-beta incorporated into the backbone, thus increasing the length of the protein backbone by one methylene unit. This post-translation modification is suspected to contribute to the aging of proteins and to protein folding disorders such as Alzheimer's disease, so that differentiating the two isomers becomes important. This manuscript reports that distinguishing aspartyl from isoaspartyl residues in peptides has been accomplished by electron capture dissociation (ECD) using a Fourier transform mass spectrometer (FTMS). Model peptides with aspartyl residues and their isoaspartyl analogs were examined and unique peaks corresponding to C-n(.)+58 and z(theta-n)-57 fragment ions (n, position of Asp; E, total number of amino acids in the peptide) were found only in the spectra of the peptides with isoaspartyl residues. The proposed fragmentation mechanism involves cleavage of the C.-C backbone bond, therefore splitting the isoasZ partyl residue between the two fragments. Also, a complementary feature observed specific to aspartyl residues was the neutral loss of the aspartic acid side chain from the charge reduced species. CAD spectra of the peptides from the same instrument demonstrated the improved method because previously published CAD methods rely on the comparison to the spectra of standards with aspartyl residues. The potential use of the top-down approach to detect and resolve products from the deamidation of asparaginyl and isomerization of aspartyl residues is discussed.