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Gas-phase fragmentation reactions of a(7) ions containing a glutamine residue

2021    Atik, Ahmet; Arslanoglu, Alper; Yalcin, Talat

The gas-phase fragmentation reactions of the a(7) ions derived from glutamine (Q) containing model heptapeptides have been studied in detail with low-energy collision-induced dissociation (CID) tandem mass spectrometry (MS/MS). Specifically, the positional effect of the Q residue has been investigated on the fragmentation reactions of a(7) ions. The study involves two sets of permuted isomers of the Q containing model heptapeptides. The first set contains the QAAAAAA sequence, and the second set involves of QYAGFLV sequence, where the position of the Q residue is changed from N- to C-terminal gradually for both peptide series. An intense loss of ammonia from the a7 ions followed by internal amino acid eliminations strongly supports forming the imine-amides structure via cyclization/rearrangement reaction for all studied a(7) ions. This is in agreement with the pioneering study reported by Bythell et al. (2010, 10.1021/ja101556g). A novel rearrangement reaction is detected upon fragmentation of imine-amide structure, which yields a protonated C-terminal amidated hexapeptide excluding the Q residue. A possible fragmentation mechanism was proposed to form the protonated C-terminal amidated hexapeptide, assisted via nucleophilic attack of the side chain amide nitrogen of the Q residue on its N-protonated imine carbon atom of the rearranged imine-amide structure. Highlights The gas-phase fragmentation reactions of a(7) ions obtained from protonated model peptides containing glutamine residue were studied by ESI-MS/MS. A rearranged imine-amide structure is the predominant even for a(7) ions. Novel rearrangement reaction is observed which forms a protonated C-terminal amidated hexapeptide excluding Q residue upon fragmentation of the imine-amide structure.