期刊
ANALYTICAL CHEMISTRY
卷 83, 期 17, 页码 6675-6682出版社
AMER CHEMICAL SOC
DOI: 10.1021/ac201223d
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资金
- EPSRC [EP/F034210/1]
- [NIH/NCRR-P41 RR10888]
- [NIH/NIGMS-R01GM078293]
- [NIH/NCRR-S10 RR025082]
- EPSRC [EP/F034210/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/F034210/1] Funding Source: researchfish
Formation of isoaspartic acid (isoAsp) is a common modification of aspartic acid (Asp) or asparagine (Asn) residue in proteins. Differentiation of isoAsp and Asp residues is a challenging task owing to their similar properties and identical molecular mass. It was recently shown that they can be differentiated using ion-electron or ion-ion interaction fragmentation methods (ExD) because these methods provide diagnostic fragments c + 57 and z(center dot) - 57 specific to the isoAsp residue. To date, however, the presence of such fragments has not been explored on peptides with an N-terminal isoAsp residue. To address this question, several N-terminal isoAsp-containing peptides were analyzed using ExD methods alone or combined with chromatography. A diagnostic fragment [M + 2H - 74](+center dot) was observed for the doubly charged precursor ions with N-terminal isoAsp residues. For some peptides, identification of the N-terminal isoAsp residue was challenging because of the low diagnostic ion peak intensity and the presence of interfering peaks. Supplemental activation was used to improve diagnostic ion detection. Further, N-terminal acetylation was offered as a means to overcome the interference problem by shifting the diagnostic fragment peak to [M + 2H - 116](+center dot).
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