Toward a Platform for Comprehensive Glycan Sequencing

From a series of recently published reports, an analytical platform has been proposed for a quantitative and qualitative measure of N- and O-glycosylation, complete with peptide-glycan connectivity and detailed structural understanding. As distant as this may appear, a best methods approach will appear that must move us beyond the cartoon stage of structural understanding. Thus, with this unifying goal in mind, we summarize a series of individually promising first phase protocols of sample preparation (release, purification, and quantification) that remain congruent with a concluding phase (methylation and MSn) for documented structural detail. Sequential enzymatic N-glycan and chemical O-glycan release from glycopeptides with intervening solid phase extraction and derivatization will provide for a comparative quantification measure of glycosylation. The O-glycan release will be nonreductive and coupled with Michael addition to a pyrazolone analog (1-phenyl-3-methyl-5-pyrazolone) with both the peptide and glycan labeled. The product glycans are stable to methylation and appropriate for sequential disassembly (MSn). An application using human serum and cancer samples has been detailed characterizing sLex and comparable valence epitopes. This integrated platform will provide opportunities at variable points to contrast, share, and advance alternative protocols in a collaborative effort that is greatly needed. This integrated platform provides end point opportunities to confirm structural details compiled from synthetic standards and well characterized biologics by MSn.