Delineating multiple N- and O-glycosylation sites on single glycopeptides and deriving more glycan structure information to discriminate isomeric glycoforms are practical problems to be tackled. Negative mode MS2/MS3 fragmentation was investigated and developed to supplement current nanoLC-MS2-based sequencing and identification of intact glycopeptides largely performed in positive mode. We found that sulfation and sialylation drastically alter the MS2 fragmentation pattern of glycopeptides in negative mode and the characteristic features identified can be utilized to program the MS3 on the glycan moiety itself. Direct elimination of one or more O-glycans affords an easy way to discover additional O-glycosylations on a multiply glycosylated peptide by virtue of enumerating the dehydration scars imprinted on the O-glycosylated sites. Moreover, the characteristic peptide core ion can be relied upon to filter out all related N-glycopeptides carrying additional O-glycans. Such enhanced ability is anticipated to have a significant impact in glycoproteomic applications.
論文名稱：“Strategic applications of negative mode LC-MS/MS analyses to expedite confident mass spectrometry-based identification of multiple glycosylated peptides”
作者群：Chu-Wei Kuo, Kay-Hooi Khoo