Isotope Labeling of N-linked Glycans by Transglycosylation of Endo-M and Isotopic Glucose for Quantitative Glycomics

To understand the biological relevance of glycans, many mass spectrometry (MS)-based methods have been developed for the relative quantification of N-linked glycans using stable isotopic labeling. The increasing demand for the simultaneous comparative quantification of N-linked glycans for samples of various biological conditions is a new challenge for MS. We proposed a novel relative quantitative glycomics that enzymatically incorporates isotope-labeled glucose into N-linked glycans through transglycosylation of endo-?-N-acetylglucosaminidase M (Endo-M) and isotope-labeled glucose. Newly incorporated normal (light) and isotope-labeled (heavy) N-linked glycans were synthesized using the same known concentration of sialyglycopeptide, and their relative quantitative properties were realized from the duplex mass spectrum. In addition, the dynamic range and accuracy of the relative quantification were shown with light and heavy N-linked glycans for sialyglycopeptide at a constant concentration ratio.