Hydrophilic Interaction Chromatography Based Enrichment of Glycopeptides by Using Click Maltose: A Matrix with High Selectivity and Glycosylation Heterogeneity Coverage

Glycosylation analysis based on mass spectrometry (MS) of glycopeptides requires the isolation of glycopeptides from complex glycoprotein digests to facilitate structural determination of the glycopeptides. To this end, hydrophilic interaction chromatography (HILIC)-based methods have been developed to selectively enrich glycopeptides by utilizing the hydrophilicity of the glycans. However, the application of these methods is limited by the medium selectivity of HILIC matrices. To improve the effectiveness of HILIC-based methods, we introduced a customized hydrophilic matrix named "click maltose" and characterized its selectivity and glycosylation heterogeneity coverage. In the selectivity assessment, the non-glycopeptides causing ion suppression to the glycopeptides were effectively removed by click maltose, leading to the identification of 27 glycopeptides in the fractions enriched from human serum immunoglobulin G digest, compared to 13 glycopeptides enriched using Sepharose CL-6B, a commercially available matrix. For the assessment of glycosylation heterogeneity coverage, more than 140 glycopeptides covering all the five glycosites of human serum alpha(1)-acid glycoprotein were captured using click maltose. Click maltose was synthesized by linking alkynyl-derivatized maltose to azide-derivatized silica through click chemistry. The resulting flexible saccharide chain structure remarkably enhances the hydrogen-bonding interactions between the glycans of the glycopeptides and the matrix, which are responsible for the increased selectivity and glycosylation heterogeneity coverage of click maltose.