Ab initio DFT Study on the Fragmentation Mechanism of Proton Adducts of A Phosphorylated Tetrapeptide in Collision-Induced Dissociations

摘要

Deciphering the structure of peptides with post -translational modification is an exciting challenge for Mass Spectrometry, because t he occurrence of facile neutral losses of H_3PO_4 and/or HPO_3 from protonated phosphopeptides makes it difficult to determine both the site of phosphorylation and the amino acid sequence. While fragments in ECD and ETD retain post -translational modification such as phosphorylation [1-3], conventional low energy CAD/CID of phosphopeptides typically leads to dissociation of a phosphorylation modification during fragmentation. However, the "On - Resonance" pulsed gas introduction CID mainly reduced neutral losses and improved sequence coverage [4]. In this paper, the fragmentation processes from the protonated phosphopeptide pYYRK were investigated using ab initio DFT calculations. Fragmentation mechanisms in both "On-Resonance" and "Off-Resonance" pulsed gas introduction CID are discussed.