Protein glycosylation plays key roles in many biological processes. In addition, alterations in protein glycosylation have been related to different diseases, as well as may affect the properties of recombinant proteins used as human therapeutics. For this reason, protein glycosylation analysis is of main interest in biomedical and biopharmaceutical research. Although recent advances in LC-MS analysis have made possible glycoprotein glycosylation site identification, characterization of glycoprotein glycan structures, as well as glycoprotein identification and quantification, protein glycosylation analysis in complex samples still remains a difficult task. This is due to low proportions of glycopeptides in comparison to peptides obtained after glycoprotein digestion, the suppression of the glycopeptide MS signals in the presence of peptides, and the high heterogeneity of glycopeptides. Thus, in the recent years, continuous efforts have been devoted to the development of glycopeptide enrichment and separation strategies to facilitate and improve glycoprotein glycosylation analysis in complex samples. This review summarizes the different methodologies that can be employed for glycopeptide enrichment/separation from complex samples including methods based on lectin affinity enrichment, covalent interactions, or chromatographic separations and solid-phase extraction.
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