Negative Ion CID Fragmentation of O-linked Oligosaccharide Aldoses—Charge Induced and Charge Remote Fragmentation

• Published in: Journal of the American Society for Mass Spectrometry 2011-06, Vol.22 (6), p.1052, Article s13361-011-0102-3
• Main Authors: Doohan, Roisin A., Hayes, Catherine A., Harhen, Brendan, Karlsson, Niclas Göran
• Format: Article
• Language: English
• Subjects: Acetylgalactosamine - chemistry; Analytical Chemistry; Analytisk kemi; Bioinformatics; Biotechnology; Chemistry; Chemistry and Materials Science; Chromatography, Liquid; electrospray; Fragmentation; Fragments; Glycomics; Graphite - chemistry; Ions - chemistry; Mass spectrometry; N-Acetylneuraminic Acid - chemistry; o-linked oligosaccharides; Oligosaccharides; Oligosaccharides - chemistry; Organic Chemistry; Proteomics; Research Article; Spectrometry, Mass, Electrospray Ionization - methods; Sugar Alcohols - chemistry; Sulfates - chemistry
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1007/s13361-011-0102-3

Collision induced dissociation (CID) fragmentation was compared between reducing and reduced sulfated, sialylated, and neutral O- linked oligosaccharides. It was found that fragmentation of the [M – H] – ions of aldoses with acidic residues gave unique Z-fragmentation of the reducing end GalNAc containing the acidic C-6 branch, where the entire C-3 branch was lost. This fragmentation pathway, which is not seen in the alditols, showed that the process involved charge remote fragmentation catalyzed by a reducing end acidic anomeric proton. With structures containing sialic acid on both the C-3 and C-6 branch, the [M – H] – ions were dominated by the loss of sialic acid. This fragmentation pathway was also pronounced in the [M – 2H] 2– ions revealing both the C-6 Z-fragment plus its complementary C-3 C-fragment in addition to glycosidic and cross ring fragmentation. This generation of the Z/C-fragment pairs from GalNAc showed that the charges were not participating in their generation. Fragmentation of neutral aldoses showed pronounced Z-fragmentation believed to be generated by proton migration from the C-6 branch to the negatively charged GalNAc residue followed by charge remote fragmentation similar to the acidic oligosaccharides. In addition, A-type fragments generated by charge induced fragmentation of neutral oligosaccharides were observed when the charge migrated from C-1 of the GalNAc to the GlcNAc residue followed by rearrangement to accommodate the 0,2 A-fragmentation. LC-MS also showed that O- linked aldoses existed as interchangeable α/β pyranose anomers, in addition to a third isomer (25% of the total free aldose) believed to be the furanose form.