Hevesy György PhD School of Chemistry, ELTE Eötvös Loránd University, Budapest, Hungary.
MTA-ELTE Research Group of Peptide Chemistry, Department of Organic Chemistry, ELTE Eötvös Loránd University, Budapest, Hungary.
J Am Soc Mass Spectrom. 2019 Sep;30(9):1586-1591. doi: 10.1007/s13361-019-02271-x. Epub 2019 Jul 12.
Tandem mass spectrometry of peptides is of utmost importance in proteomics. Collision-induced dissociation usually generates y type fragment ion series from tryptic peptides, carrying information on their primary structure. Amino acid side chains or differences in their basicity could alter fragmentation processes considerably. The well-known proline effect is a cleavage preference at the N-terminus of proline residues in peptides, usually yielding a very abundant y ion while suppressing others. Previously, we reported a similar phenomenon occurring at the C-terminus of citrulline residues and coined the term Cit effect. To confirm the presence of Cit effect in large proteomic datasets, we analyzed 293 peptides containing Cit residues based on the human proteome database mining work of Lee et al. (2018). The occurrence of Cit effect was found to be 44%. Comparing bond scissions at the amide linkage between Cit-Zzz (citrulline followed by a specified residue) to Aaa-Aaa (Aaa can be any residue except Cit), 5 Cit-Zzz cleavages were significantly (CL = 95.0%) more frequent in > 85% of the cases in terms of relative sequential base beak occurrence. We used Pro effect to compare with Cit effect and obtained very similar results. On the other hand, our study showed that Cit effect is slightly inferior in the overall incidence to Pro effect (50% vs. 33%, CL = 95%) among deiminated peptides when Pro residues were also present in the sequence. Our results suggest that Cit effect is a characteristic feature and a possible biasing factor of deiminated peptides which can confirm the position of citrullination sites.
串联质谱肽在蛋白质组学中非常重要。碰撞诱导解离通常会从胰蛋白酶肽中产生 y 型片段离子系列，这些离子系列携带有关其一级结构的信息。氨基酸侧链或其碱性的差异可能会极大地改变碎片化过程。众所周知的脯氨酸效应是肽中脯氨酸残基 N 末端的优先裂解，通常会产生非常丰富的 y 离子，同时抑制其他离子。以前，我们报道了在瓜氨酸残基的 C 末端发生类似的现象，并将其命名为 Cit 效应。为了在大型蛋白质组学数据集中确认 Cit 效应的存在，我们根据 Lee 等人（2018 年）的人类蛋白质组数据库挖掘工作分析了 293 个含有 Cit 残基的肽。发现 Cit 效应的发生率为 44%。比较 Cit-Zzz（瓜氨酸后面跟着一个指定的残基）和 Aaa-Aaa（Aaa 可以是任何残基，除了 Cit）之间酰胺键的断裂，在 >85%的情况下，5 个 Cit-Zzz 裂解在相对顺序碱基断裂发生的情况下明显（CL=95.0%）更频繁。我们使用 Pro 效应进行比较，并得到了非常相似的结果。另一方面，我们的研究表明，当序列中也存在 Pro 残基时，Cit 效应在脱氨肽中的总体发生率（50%对 33%，CL=95%）略低于 Pro 效应。我们的研究结果表明，Cit 效应是脱氨肽的一个特征性特征和可能的偏倚因素，可以确认瓜氨酸化位点的位置。
