Electron Transfer Dissociation with Supplemental Activation to Differentiate Aspartic and Isoaspartic Residues in Doubly Charged Peptide Cations

• Published in: Journal of the American Society for Mass Spectrometry 2010-06, Vol.21 (6), p.1012-1015
• Main Authors: Chan, Wai Yi Kelly, Chan, T.W. Dominic, O'Connor, Peter B.
• Format: Article
• Language: English
• Subjects: Acids; Activation; Amino Acid Sequence; Analytical Chemistry; Aspartic acid; Aspartic Acid - chemistry; Backbone; Bioinformatics; Biotechnology; Cations; Cations - chemistry; Charging; Chemistry; Chemistry and Materials Science; Diagnostic systems; Electron transfer; Glutamic acid; Ions; Isoaspartic Acid - chemistry; Mass spectrometry; Mass Spectrometry - methods; Molecular Sequence Data; Organic Chemistry; Peptide Fragments - chemistry; Peptide Fragments - metabolism; Peptides; Proteomics; Residues; Short Communication
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/j.jasms.2010.02.002

Electron-transfer dissociation (ETD) with supplemental activation of the doubly charged deamidated tryptic digested peptide ions allows differentiation of isoaspartic acid and aspartic acid residues using the c + 57 or z • − 57 peaks. The diagnostic peak clearly localizes and characterizes the isoaspartic acid residue. Supplemental activation in ETD of the doubly charged peptide ions involves resonant excitation of the charge reduced precursor radical cations and leads to further dissociation, including extra backbone cleavages and secondary fragmentation. Supplemental activation is essential to obtain a high quality ETD spectrum (especially for doubly charged peptide ions) with sequence information. Unfortunately, the low-resolution of the ion trap mass spectrometer makes detection of the diagnostic peak, [M-60], for the aspartic acid residue difficult due to interference with side-chain loss from arginine and glutamic acid residues. Supplemental activation (collisional heating) of peptide ions is often required to observe the diagnostic c + 57/z − 57 peaks that determine the position of isoaspartic acid (β-aspartic acid) residues.