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Gas-Phase Fragmentation Reactions of A7 Ions Containing a Glutamine Residue
(Wiley-Blackwell, 2021) Atik, Ahmet; Arslanoğlu, Alper; Yalçın, Talat; Atik, Ahmet; Arslanoğlu, Alper; Yalçın, Talat
The gas-phase fragmentation reactions of the a7 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 a7 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 a7 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 a7 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 a7 ions. Novel rearrangement reaction is observed which forms a protonated C-terminal amidated hexapeptide excluding Q residue upon fragmentation of the imine-amide structure.
Citation - WoS: 9
Citation - Scopus: 9
The Role of Lysine ?-Amine Group on the Macrocyclization of B Ions
(Elsevier Ltd., 2012) Atik, Ahmet Emin; Görgülü, Güvenç; Yalçın, Talat
A study was carried out to examine if the amine (NH 2) group located on the side chains of lysine (K), glutamine (Q), or asparagine (N) residue has any effect on the macrocyclization of b ions even though the N-terminals of the peptides were acetylated. The work utilized the model peptides Ac-KYAGFLVG, Ac-QYAGFLV-NH 2, and Ac-NYAGFLV-NH 2. The CID mass spectra of b 7 ions originated from these three peptides exhibited that the macrocyclization still occurred for the lysine containing peptide in spite of the N-terminal of the peptide was acetylated, but was failed to be observed for glutamine and asparagine containing peptides. These current results reveal that the lysine side chain ε-amine group has been involved in the macrocyclization of the peptide b ions for the N-terminal acetylated peptides and consequently, non-direct sequence b ions were observed in the CID mass spectra. However, due to the amide group on the side chains of the glutamine and asparagine residues, the nucleophilicity of their groups greatly reduced; therefore the scrambling b ions were not detected in their b 7 ion CID mass spectra. In addition, the effect of the lysine position was also studied for series of six isomeric octapeptides such as, Ac-KYAGFLVG, Ac-YKAGFLVG, Ac-YAKGFLVG, Ac-YAGKFLVG, Ac-YAGFKLVG and Ac-YAGFLKVG in order to examine the relationship between the intensities of non-direct sequence b ions and the lysine position in the octapeptide series. The results clearly demonstrated that the most abundant non-direct sequence b ions were observed for the first position of lysine residue in the N-terminal acetylated octapeptide, however, when the lysine residue gets closer to the C-terminal position the relative intensities of the scrambled b ions were greatly decreased.

Chemistry / Kimya

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