A Systematic Study of Acidic Peptides for b-Type Sequence Scrambling |
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Authors: | A Emin Atik Talat Yalcin |
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Institution: | (1) Department of Chemistry, Faculty of Science, Izmir Institute of Technology, 35430 Urla-Izmir, Turkey; |
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Abstract: | A systematic study was carried out to examine the effects of acidic amino acid residues and the position of the acidic group
on the cyclization of b ions. The study utilized the model C-terminal amidated peptides XAAAAAA, AXAAAAA, AAXAAAA, AAAXAAA, AAAAXAA, AAAAAXA, AAAAAAX,
XXAAAAAA, AAXXAAAA, AAAAXXAA, and AAAAAAXX, where X is a glutamic acid (E) or aspartic acid (D) residue. The CID mass spectra
of b
n
(where n = 7 and 8) ions derived from XAAAAAA, AAAXAAA, AAAAAAX and XXAAAAAA, AAXXAAAA, AAAAXXAA, and AAAAAAXX exhibited very similar
fragmentation patterns for both the glutamic and the aspartic acid peptide series. The CID mass spectra of MH+ derived from model peptides presented substantial direct and non-direct sequence b ions. The results indicate that b ions produced from acidic peptides can also undergo head-to-tail cyclization, which is the reason for the formation of the
non-direct sequence b ions. The b ion spectra derived from the peptides became more complex as the number of acidic residues in the peptides increased. Side
chains of glutamic and aspartic acid did not inhibit the cyclization of the b ions. Substantial water elimination was observed in all CID spectra of b
7 and b
8 ions. Finally, the preferential cleavage of glutamic or aspartic acid residues from macrocyclic structures of b ions was also investigated under various collision energy conditions. |
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Keywords: | |
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