Specific rearrangement reactions of acetylated lysine containing peptide b_n (n = 4–7) ion series

Abstract

Characterization of ε-N-acetylated lysine containing peptides, one of the most prominent post-translational modifications of proteins, is an important goal for tandem mass spectrometry experiments. A systematic study for the fragmentation reactions of b ions derived from ε-N-acetyllysine containing model octapeptides (K Ac YAGFLVG and YAK Ac GFLVG) has been examined in detail. Collision-induced dissociation (CID) mass spectra of b n (n = 4-7) fragments of ε-N-acetylated lysine containing peptides are compared with those of N-terminal acetylated and doubly acetylated (both ε-N and N-terminal) peptides, as well as acetyl-free peptides. Both direct and nondirect fragments are observed for acetyl-free and singly acetylated (ε-N or N-terminal) peptides. In the case of ε-N-acetylated lysine containing peptides, however, specific fragment ions (m/z 309, 456, 569 and 668) are observed in CID mass spectra of b n (n = 4-7) ions. The CID mass spectra of these four ions are shown to be identical to those of selected protonated C-terminal amidated peptides. On this basis, a new type of rearrangement chemistry is proposed to account for the formation of these fragment ions, which are specific for ε-N-acetylated lysine containing peptides. Consistent with the observation of nondirect fragments, it is proposed that the b ions undergo head-to-tail macrocyclization followed by ring opening. The proposed reaction pathway assumes that b n (n = 4-7) of ε-N-acetylated lysine containing peptides has a tendency to place the K Ac residue at the C-terminal position after macrocyclization/reopening mechanism. Then, following the loss of CO, it is proposed that the marker ions are the result of the loss of an acetyllysine imine as a neutral fragment.

Benzophenone Photoreactivity in a Lipid Bilayer To Probe Peptide/Membrane Interactions: Simple System, Complex Information

“…Other ions are reproducibly observed with similar relative intensities, in the low mass range in all MS/MS spectra. They correspond to Pen b-ions as well as ions at m / z 209, 259, and 292, the structures of which are shown in Figure (ions 1, 2, 4) according to mechanisms published in the literature . A structure is proposed for the ion at m / z 331 (ion 6) observed with DOPG.…”

“…They correspond to Pen b-ions as well as ions at m/z 209, 259, and 292, the structures of which are shown in Figure 5 (ions 1, 2, 4) according to mechanisms published in the literature. 31 A structure is proposed for the ion at m/z 331 (ion 6) observed with DOPG.…”