Glycoproteome Analysis of Human Serum and Brain Tissue

Protein glycosylation represents one of the most common and heterogeneous post-translational modifications (PTMs) in human biology. Herein, an approach for the enrichment of glycopeptides using multi-lectin weak affinity chromatography (M-LWAC), followed by fractionation of the enriched material, and multi-mode fragmentation LC/MS is described. Two fragmentation methods, high-energy collision induced dissociation (HCD) and electron transfer dissociation (EThcD), were independently analyzed. While each fragmentation method provided similar glycopeptide coverage, there was some dependence on the glycoform identity. From these data a total of 7,503 unique glycopeptides belonging to 666 glycoproteins from the combined tissue types, human serum and brain, were identified. Of these, 617 glycopeptides (192 proteins) were found in both tissues; 2,006 glycopeptides (48 proteins) were unique to serum, and 4,880 glycopeptides (426 proteins) were unique to brain tissue. From 379 unique glycoforms, 1,420 unique sites of glycosylation were identified, with an average of four glycans per site. Glycan occurrences were significantly different between tissue types: serum showed greater glycan diversity whereas brain tissue showed a greater abundance of the high mannose family. Glycosylation co-occurrence rates were determined, which enabled us to infer differences in underlying biosynthetic pathways.