Structure and further fragmentation of significant [a3 + Na − H]+ ions from sodium‐cationized peptides |
| |
Authors: | Huixin Wang Bing Wang Zhonglin Wei Hao Zhang Xinhua Guo |
| |
Institution: | 1. College of Chemistry, Jilin University, Changchun, China;2. State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun, China |
| |
Abstract: | A good understanding of gas‐phase fragmentation chemistry of peptides is important for accurate protein identification. Additional product ions obtained by sodiated peptides can provide useful sequence information supplementary to protonated peptides and improve protein identification. In this work, we first demonstrate that the sodiated a3 ions are abundant in the tandem mass spectra of sodium‐cationized peptides although observations of a3 ions have rarely been reported in protonated peptides. Quantum chemical calculations combined with tandem mass spectrometry are used to investigate this phenomenon by using a model tetrapeptide GGAG. Our results reveal that the most stable a3 + Na ? H]+ ion is present as a bidentate linear structure in which the sodium cation coordinates to the two backbone carbonyl oxygen atoms. Due to structural inflexibility, further fragmentation of the a3 + Na ? H]+ ion needs to overcome several relatively high energetic barriers to form b2 + Na ? H]+ ion with a diketopiperazine structure. As a result, low abundance of b2 + Na ? H]+ ion is detected at relatively high collision energy. In addition, our computational data also indicate that the common oxazolone pathway to generate b2 + Na ? H]+ from the a3 + Na ? H]+ ion is unlikely. The present work provides a mechanistic insight into how a sodium ion affects the fragmentation behaviors of peptides. Copyright © 2015 John Wiley & Sons, Ltd. |
| |
Keywords: | sodium‐ion‐associated peptide a3 ions b2 ion structure charge‐remote fragmentation pathway diketopiperazine |
|
|