Department of Chemistry, The University of Alabama, Tuscaloosa, AL, 35487, USA.
Department of Chemistry, The University of Georgia, Athens, GA, 30602, USA.
J Am Soc Mass Spectrom. 2016 May;27(5):847-55. doi: 10.1007/s13361-016-1345-9. Epub 2016 Feb 10.
Matrix-assisted laser desorption/ionization (MALDI) in-source decay was studied in the negative ion mode on deprotonated peptides to determine its usefulness for obtaining extensive sequence information for acidic peptides. Eight biological acidic peptides, ranging in size from 11 to 33 residues, were studied by negative ion mode ISD (nISD). The matrices 2,5-dihydroxybenzoic acid, 2-aminobenzoic acid, 2-aminobenzamide, 1,5-diaminonaphthalene, 5-amino-1-naphthol, 3-aminoquinoline, and 9-aminoacridine were used with each peptide. Optimal fragmentation was produced with 1,5-diaminonphthalene (DAN), and extensive sequence informative fragmentation was observed for every peptide except hirudin(54-65). Cleavage at the N-Cα bond of the peptide backbone, producing c' and z' ions, was dominant for all peptides. Cleavage of the N-Cα bond N-terminal to proline residues was not observed. The formation of c and z ions is also found in electron transfer dissociation (ETD), electron capture dissociation (ECD), and positive ion mode ISD, which are considered to be radical-driven techniques. Oxidized insulin chain A, which has four highly acidic oxidized cysteine residues, had less extensive fragmentation. This peptide also exhibited the only charged localized fragmentation, with more pronounced product ion formation adjacent to the highly acidic residues. In addition, spectra were obtained by positive ion mode ISD for each protonated peptide; more sequence informative fragmentation was observed via nISD for all peptides. Three of the peptides studied had no product ion formation in ISD, but extensive sequence informative fragmentation was found in their nISD spectra. The results of this study indicate that nISD can be used to readily obtain sequence information for acidic peptides.
基质辅助激光解吸/电离（MALDI）在负离子模式下对去质子化肽进行源内降解研究，以确定其在获得酸性肽广泛序列信息方面的有用性。八种大小在 11 到 33 个残基之间的生物酸性肽通过负离子模式 ISD（nISD）进行研究。使用每种肽与 2,5-二羟基苯甲酸、2-氨基苯甲酸、2-氨基苯甲酰胺、1,5-二氨基萘、5-氨基-1-萘酚、3-氨基喹啉和 9-氨基吖啶作为基质。对于每个肽，最优的片段化是用 1,5-二氨基萘（DAN）产生的，除了水蛭素（54-65）之外，对于每个肽都观察到了广泛的序列信息片段化。肽主链的 N-Cα 键的裂解，产生 c'和 z'离子，对于所有肽都是主要的。未观察到脯氨酸残基 N 末端的 N-Cα 键的裂解。c 和 z 离子的形成也存在于电子转移解离（ETD）、电子俘获解离（ECD）和正离子模式 ISD 中，这些被认为是自由基驱动的技术。具有四个高度酸性氧化半胱氨酸残基的氧化胰岛素链 A 具有较少的广泛片段化。该肽还表现出唯一的带电荷局部片段化，在高度酸性残基附近具有更明显的产物离子形成。此外，还为每个质子化肽获得了正离子模式 ISD 的光谱；通过 nISD 观察到所有肽都具有更多的序列信息片段化。在所研究的三种肽中，ISD 没有产物离子形成，但在其 nISD 光谱中发现了广泛的序列信息片段化。这项研究的结果表明，nISD 可用于轻松获得酸性肽的序列信息。
