Structural analysis of N-glycans by the glycan-labeling method using 3-aminoquinoline-based liquid matrix in negative-ion MALDI-MS.
Negative-ion fragmentation of underivatized N-glycans has been proven to be more informative than positive-ion fragmentation. Fluorescent labeling via reductive amination is often employed for glycan analysis, but little is known about the influence of the labeling group on negative-ion fragmentation. We previously demonstrated that the on-target glycan-labeling method using 3-aminoquinoline/α-cyano-4-hydroxycinnamic acid (3AQ/CHCA) liquid matrix enables highly sensitive, rapid, and quantitative N-glycan profiling analysis. The current study investigates the suitability of 3AQ-labeled N-glycans for structural analysis based on negative-ion collision-induced dissociation (CID) spectra. 3AQ-labeled N-glycans exhibited simple and informative CID spectra similar to those of underivatized N-glycans, with product ions due to cross-ring cleavages of the chitobiose core and ions specific to two antennae (D and E ions). The interpretation of diagnostic fragment ions suggested for underivatized N-glycans could be directly applied to the 3AQ-labeled N-glycans. However, fluorescently labeled N-glycans by conventional reductive amination, such as 2-aminobenzamide (2AB)- and 2-pyrydilamine (2PA)-labeled N-glycans, exhibited complicated CID spectra consisting of numerous signals formed by dehydration and multiple cleavages. The complicated spectra of 2AB- and 2PA-labeled N-glycans was found to be due to their open reducing-terminal N-acetylglucosamine (GlcNAc) ring, rather than structural differences in the labeling group in the N-glycan derivative. Finally, as an example, the on-target 3AQ labeling method followed by negative-ion CID was applied to structurally analyze neutral N-glycans released from human epidermal growth factor receptor type 2 (HER2) protein. The glycan-labeling method using 3AQ-based liquid matrix should facilitate highly sensitive quantitative and qualitative analyses of glycans.
Koichi Tanaka Laboratory of Advanced Science and Technology, Shimadzu Corporation, 1, Nishinokyo-Kuwabaracho, Nakagyo-ku, Kyoto 604-8511, Japan. nishikaz@shimadzu.co.jp
Takashi
T
Nishikaze
Kaoru
K
Kaneshiro
Shin-ichirou
S
Kawabata
Koichi
K
Tanaka
D000634:Aminoquinolines / Q000737:chemistry*; D006801:Humans; D010446:Peptide Fragments / Q000737:chemistry; D011134:Polysaccharides / Q000032:analysis* / Q000737:chemistry*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013194:Staining and Labeling
D000634:Aminoquinolines; D010446:Peptide Fragments; D011134:Polysaccharides; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human