The role of lysine ɛ-amine group on the macrocyclization of b ions

Abstract

a b s t r a c tA 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 -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.

Exploitation of the Ornithine Effect Enhances Characterization of Stapled and Cyclic Peptides

“…Upon collisional activation of an ornithine-containing peptide, the amine of the ornithine residue cyclizes via nucleophilic attack at the adjacent carbonyl group, resulting in a characteristic and preferential cleavage C-terminal to the carbonyl group. This phenomenon has been observed before, as lysine and many of its homologues have exhibited similar characteristics as a nucleophile previously [42][43][44][45].…”

Low energy CID and action IRMPD provide insights into a minor subpopulation of the gas-phase conformers of triply charged bradykinin

“…Action infrared multi-photon dissociation (IRMPD) spectroscopy, hydrogen/deuterium exchange (HDX), and computational modeling data all support the 5-membered oxazolone ring as the dominant b ion structure, although macrocyclic structures have also been shown to form. [4][5][6][7][8][9][10][11][12][13] These structures have received much interest because ring opening of the macrocycle can lead to scrambling the original peptide sequence. [11,[14][15][16][17] The smallest of the b ions, the b 2 ion, has also been particularly well studied because it can have either a diketopiperazine or oxazolone structure and the preferential formation of one of these structures over the other has been repeatedly shown to be related to amino acid sequence in the first three positions of the peptide.…”

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

“…The m/z 651 ion was observed as the most abundant fragment ion in the CID-MS 4 mass spectrum, and the further isolation (CID-MS 5 ) of the m/z 651 ion have resulted the same CID mass spectra of b 6 ions derived from permuted isomers of YAGFLV-NH 2 , whose CID mass spectra have been reported from our group previously. [36,37] The CID mass spectrum of m/z 668 fragment from b 7 ion of protonated K Ac YAGFLVG and YAGFLV-NH 2 peptides is given in Fig. 2(a).…”

“…When the N-terminal of the lysine containing peptide was acetylated, the observation of nondirect fragment ions suggested that lysine ε-amine group could attack to the carbonyl carbon of the oxazolone ring (side-to-tail cyclization) to form macrocyclic structure of b ion. [36] Doubly acetylated peptide, Ac-K Ac YAGFLVG, in which both of the α-amine of the peptide and ε-amine of lysine residue have been acetylated, was also investigated. As shown in Fig.…”