Identification, quantification, and characterization of glycopeptides in reversed-phase HPLC separations of glycoprotein proteolytic digests.

Monosaccharide analysis by high pH anion-exchange chromatography with pulsed amperometric detection (HPAEC/PAD) was used to identify the glycopeptides in the reversed-phase (RP-HPLC) separation of a bovine fetuin tryptic digest (1.6 nmol). This method, requiring no sample derivatization, identified four asparagine-linked (N-linked) glycopeptides and at least seven serine/threonine-linked (O-linked) glycopeptides. Glycopeptide identification was confirmed by Edman sequencing. Monosaccharide quantification of each glycopeptide suggested that all of the N-linked glycopeptides were the complex type and all the O-linked glycopeptides were sialylated. We determined that glycopeptides could be prepared by acidic reversed-phase chromatography with less than 3% loss of N-acetylneuraminic acid (Neu5Ac). The N-linked glycopeptides of bovine fetuin were prepared, digested with N-glycosidase F (PNGase F), and their oligosaccharides analyzed by HPAEC/PAD. These oligosaccharide profiles revealed that the Asn-138 oligosaccharide attachment site contained the majority of the disialylated and monosialylated oligosaccharides. The Asn-158 oligosaccharide attachment site contained the majority of the tetrasialylated oligosaccharides.