There is growing evidence about the biological significance of extracellular glycosylation. The oligosaccharide structures control cell adhesion processes; affect cell to cell recognition, including pathogen identification by host cells; direct enzymatic processing; and influence intracellular signaling processes. Analysis of released glycan pools provides detailed structural information about the oligosaccharides, but not in a protein- and site-specific manner. Mass spectrometric analysis of intact glycopeplides provides valuable information about the glycan structures that modify any given N- or O-linked modification site. Immense site-specific heterogeneity in glycosylation is a well known phenomenon. Intereslingly, the capping sialic acids may introduce an additional layer of complexity.
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