Hydrophilic Nanocomposite Functionalized by Carrageenan for the Specific Enrichment of Glycopeptides

A hydrophilic nanocomposite was synthesized by an easy route to improve glycopeptides enrichment efficiency. This new composite, prepared with a method based on electrostatic interaction, was demonstrated to be efficient for immobilization of carrageenan on graphene oxide/poly­(ethylenimine) support (denoted as GO–PEI–Carr). Carrageenan, which has a large number of hydroxyl groups and is fully negatively charged, is a new modified phase of hydrophilic materials in glycoproteomics. The introduction of carrageenan provided the composite not only a perfect surface charge but also a greater ability to enrich glycosylated peptides. Thirty-four glycopeptides from human serum immunoglobulin G (IgG) tryptic digests were obviously observed with greatly improved signal-to-noise (S/N) ratio. A good selectivity was still kept even when the molar ratio of IgG and bovine serum albumin (BSA) tryptic digest mixtures reached to 1:500. Meanwhile, 76 glycopeptides derived from 56 glycoproteins with 83 N-glycosylation sites were identified from human serum and 149 glycopeptides derived from 129 glycoproteins with 157 N-glycosylation sites were identified from mouse liver tissues, which showed the ability to enrich glycopeptides from complex biological samples. In addition, GO–PEI–Carr exhibited a unique repeatability and stability even after enrichment of glycopeptides for 20 times. It also performed a higher sensitivity (1 fmol/μL IgG), a better enrichment capacity (up to ∼300 mg/g), and an ideal enrichment recovery (90.8% and 109.5%) for glycopeptides enrichment, indicating a great potential for the application of glycoproteomic research.