Research Article

Journal of The American Society for Mass Spectrometry

, Volume 22, Issue 3, pp 480-491

Unusual Fragmentation of β-Linked Peptides by ExD Tandem Mass Spectrometry

  • Nadezda P. SargaevaAffiliated withMass Spectrometry Resource, Department of Biochemistry, Boston University School of Medicine
  • , Cheng LinAffiliated withMass Spectrometry Resource, Department of Biochemistry, Boston University School of Medicine
  • , Peter B. O’ConnorAffiliated withMass Spectrometry Resource, Department of Biochemistry, Boston University School of MedicineDepartment of Chemistry, University of Warwick Email author 

Abstract

Ion-electron reaction based fragmentation methods (ExD) in tandem mass spectrometry (MS), such as electron capture dissociation (ECD) and electron transfer dissociation (ETD) represent a powerful tool for biological analysis. ExD methods have been used to differentiate the presence of the isoaspartate (isoAsp) from the aspartate (Asp) in peptides and proteins. IsoAsp is a β3-type amino acid that has an additional methylene group in the backbone, forming a Cα–Cβ bond within the polypeptide chain. Cleavage of this bond provides specific fragments that allow differentiation of the isomers. The presence of a Cα–Cβ bond within the backbone is unique to β-amino acids, suggesting a similar application of ExD toward the analysis of peptides containing other β-type amino acids. In the current study, ECD and ETD analysis of several β-amino acid containing peptides was performed. It was found that N–Cβ and Cα–Cβ bond cleavages were rare, providing few c and z type fragments, which was attributed to the instability of the Cβ radical. Instead, the electron capture resulted primarily in the formation of a and y fragments, representing an alternative fragmentation pathway, likely initiated by the electron capture at a backbone amide nitrogen protonation site within the β amino acid residues.

Key words

Ion molecule reactions Odd electron fragmentation Electron capture dissociation Electron transfer dissociation