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C α C Backbone Fragmentation Dominates in Electron Detachment Dissociation of Gas‐Phase Polypeptide Polyanions
Author(s) -
Kjeldsen Frank,
Silivra Oleg A.,
Ivonin Igor A.,
Haselmann Kim F.,
Gorshkov Mikhail,
Zubarev Roman A.
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400806
Subject(s) - electron capture dissociation , chemistry , fragmentation (computing) , tandem mass spectrometry , electron transfer dissociation , dissociation (chemistry) , mass spectrometry , ion , electron ionization , crystallography , ionic bonding , analytical chemistry (journal) , ionization , organic chemistry , chromatography , computer science , operating system
Fragmentation of peptide polyanions by electron detachment dissociation (EDD) has been induced by electron irradiation of deprotonated polypeptides [ M − n H] n − with >10 eV electrons. EDD has been found to lead preferentially to a . and x fragment ions (C α C backbone cleavage) arising from the dissociation of oxidized radical anions [ M − n H] ( n −1)− . . We demonstrate that C α C cleavages, which are otherwise rarely observed in tandem mass spectrometry, can account for most of the backbone fragmentation, with even‐electron x fragments dominating over radical a . ions. Ab initio calculations at the B3 LYP level of theory with the 6‐311+G(2 p,2 d)//6‐31+G(d,p) basis set suggested a unidirectional mechanism for EDD (cleavage always N‐terminal to the radical site), with a . , x formation being favored over a , x . fragmentation by 74.2 kJ mol −1 . Thus, backbone C α C bonds N‐terminal to proline residues should be immune to EDD, in agreement with the observations. EDD may find application in mass spectrometry for such tasks as peptide sequencing and localization of labile post‐translational modifications, for example, those introduced by sulfation and phosphorylation. EDD can now be performed not only in Fourier transform mass spectrometry, but also in far more widely used quadrupole (Paul) ion traps.