Posttranslational modifications of proteins like citrullination and carbamylation are associated with several diseases. Detailed analytical characterization of citrullinated and carbamylated proteins or peptides could be difficult due to the low concentration of the analytes in complex biological samples. High structural similarity and chemical behavior of citrullinated and carbamylated residues also pose a challenge. We previously reported the "citrulline effect" phenomenon that is manifested in the generation of intense y type ions originating from Cit-Zzz amide bond scissions in collision-induced dissociation tandem mass spectra of citrullinated tryptic peptides. In this study, we created a rigorous tryptic-like model system of both citrulline and homocitrulline-containing peptides that included appropriate and well-defined controls and fragment analogues to quantify the citrulline effect and investigate whether there is an effect for homocitrulline residues as well. Our results show that citrulline residues significantly increased fragmentation at their C-terminus relatively independent of the identity of the following amino acid. In comparison, homocitrulline residues displayed inconclusive results at the same energies. However, the strength of effects was dependent on collision energy and the position of citrulline and homocitrulline in the sequences. As newer software algorithms tend to observe structure-intensity relationships during annotation, this finding increases reliable identification of modified proteins/peptides.

中文翻译：

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瓜氨酸和高瓜氨酸残基对碰撞诱导的肽片段化影响的量化。

瓜氨酸化和氨甲酰化等蛋白质的翻译后修饰与多种疾病有关。由于复杂生物样品中分析物的浓度较低，因此很难对瓜氨酸化和氨基甲酰化的蛋白质或肽进行详细的分析表征。瓜氨酸化和氨基甲酰化残基的高结构相似性和化学行为也构成挑战。我们之前报道了“瓜氨酸效应”现象，该现象表现为在瓜氨酸化胰蛋白酶肽的碰撞诱导解离串联质谱中产生源自 Cit-Zzz 酰胺键断裂的强烈 y 型离子。在这项研究中，我们创建了一个严格的类瓜氨酸和含高瓜氨酸肽的类胰蛋白酶模型系统，其中包括适当且明确定义的对照和片段类似物，以量化瓜氨酸效应并研究是否对高瓜氨酸残基也有影响。我们的结果表明，瓜氨酸残基显着增加了其 C 端的片段化，相对独立于以下氨基酸的身份。相比之下，高瓜氨酸残基在相同能量下显示出不确定的结果。然而，效果的强度取决于碰撞能量以及瓜氨酸和高瓜氨酸在序列中的位置。由于较新的软件算法倾向于在注释过程中观察结构强度关系，