Fragmentation of AMPylated peptides: Characteristic ions and their relative peak intensity at varied collision energy

摘要

During CID MS/MS experiments of peptides containing AMPylated Ser/Thr residue, the AMP group was prone to leave the peptide. Meanwhile, AMP could also undergo further fragmentation to lose an adenine or an adenosine group. The PA values of adenine and adenosine are higher than those of most amino acids [2], which would facilitate the protonation of these leaving groups and results in characteristic ions at m/z 348.1, 136.1, and 250.1. Proton(s) can be retained on peptide fragments and form other characteristic ions: fragments with a mass shift of -347, -249, or -135 Da, respectively. Peaks at m/z 348.1, 136.1, and 250.1, fragments with AMP group attached and fragments consistent with neutral loss of 347 Da were major characteristic ions, while fragments consistent with neutral loss of 135 Da or 250 Da were weaker and not always detectable. The findings for Tyr AMPylation followed the same general patterns as those for Ser/Thr modification, with the exception that the neutral loss of AMP was not detected, so the characteristic ions of Tyr AMPylation did not include the peak at m/z 348.1, nor fragments with a mass shift of -347 Da.