Journal of the American Society for Mass Spectrometry

, Volume 21, Issue 8, pp 1352–1363

Effect of the his residue on the cyclization of b ions


  • Benjamin J. Bythell
    • Computational Proteomics GroupGerman Cancer Research Center (DKFZ)
  • Michaela Knapp-Mohammady
    • Division of Functional Genome AnalysisGerman Cancer Research Center (DKFZ)
    • Computational Proteomics GroupGerman Cancer Research Center (DKFZ)
    • Department of ChemistryUniversity of Toronto
Focus: Mobile Proton Model

DOI: 10.1016/j.jasms.2010.05.006


The MSn spectra of the [M + H]+ and b 5 peaks derived from the peptides HAAAAA, AHAAAA, AAHAAA, AAAHAA, and AAAAHA have been measured, as have the spectra of the b 4 ions derived from the first four peptides. The MS2 spectra of the [M + H]+ ions show a substantial series of bn ions with enhanced cleavage at the amide bond C-terminal to His and substantial cleavage at the amide bond N-terminal to His (when there are at least two residues N-terminal to the His residue). There is compelling experimental and theoretical evidence for formation of nondirect sequence ions via cyclization/reopening chemistry in the CID spectra of the b tons when the His residue is near the C-terminus. The experimental evidence is less clear for ions when the His residue is near the N-terminus, although this may be due to the use of multiple alanine residues in the peptide making identifying scrambled peaks more difficult. The product ion mass spectra of the b 4 and b 5 ions from these isomeric peptides with cyclically permuted amino acid sequences are similar, but also show clear differences. This indicates less active cyclization/reopening followed by fragmentation of common structures for b n ions containing His than for sequences of solely aliphatic residues. Despite more energetically favorable cyclization barriers for the b 5 structures, the b 4 ions experimental data show more clear evidence of cyclization and sequence scrambling before fragmentation. For both b 4 and b 5 the energetically most favored structure is a macrocyclic isomer protonated at the His side chain.

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© American Society for Mass Spectrometry 2010