Disulfide connectivity in peptides bearing at least two intramolecular disulfide bonds is highly important for the structure and the biological activity of the peptides. In that context, analytical strategies allowing a characterization of the cysteine pairing are of prime interest for chemists, biochemists, and biologists. For that purpose, this study evaluates the potential of MALDI in-source decay (ISD) for characterizing cysteine pairs through the systematic analysis of identical peptides bearing two disulfide bonds, but not the same cysteine connectivity. Three different matrices have been tested in positive and/or in negative mode (1,5-DAN, 2-AB and 2-AA). As MALDI-ISD is known to partially reduce disulfide bonds, the data analysis of this study rests firstly on the deconvolution of the isotope pattern of the parent ions. Moreover, data analysis is also based on the formed fragment ions and their signal intensities. Results from MS/MS-experiments (MALDI-ISD-MS/MS) constitute the last reference for data interpretation. Owing to the combined use of different ISD-promoting matrices, cysteine connectivity identification could be performed on the considered peptides.

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带有至少两个分子内二硫键的肽中的二硫键对于肽的结构和生物学活性非常重要。在这种情况下，化学家，生物化学家和生物学家最感兴趣的是能够表征半胱氨酸配对的分析策略。为此，本研究通过系统分析带有两个二硫键但不具有相同半胱氨酸连接性的相同肽，评估MALDI源内衰减（ISD）表征半胱氨酸对的潜力。已在正模式和/或负模式下测试了三种不同的矩阵（1,5-DAN，2-AB和2-AA）。由于已知MALDI-ISD可部分还原二硫键，因此本研究的数据分析首先取决于母离子的同位素模式的去卷积。而且，数据分析还基于形成的碎片离子及其信号强度。来自MS / MS实验（MALDI-ISD-MS / MS）的结果构成了数据解释的最后参考。由于不同ISD促进基质的组合使用，可以对所考虑的肽进行半胱氨酸连接性鉴定。

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