Title : Human urinary glycoproteomics; attachment site specific analysis of N- and O-linked glycosylations by CID and
ECD
Abstract :
- Urine is a complex mixture of proteins and waste products and a challenging biological fluid for biomarker discovery
- Previous proteomic studies have identified more than 2800 urinary proteins but analyses aimed at unraveling glycan structures and glycosylation sites of urinary glycoproteins are lacking
- Glycoproteomic characterization remains difficult because of the complexity of glycan structures found mainly on asparagine asparagine (N-linked) or serine/threonine (O-linked) residues
- We have developed a glycoproteomic approach that combines efficient purification of urinary glycoproteins/glycopeptides with complementary MS-fragmentation techniques for glycopeptide analysis
- Starting from clinical sample size, we eliminated interfering urinary compounds by dialysis and concentrated the purified urinary proteins by lyophilization
- Sialylated urinary glycoproteins were conjugated to a solid support by hydrazide chemistry and trypsin digested
- Desialylated glycopeptides , released through mild acid hydrolysis, were characterized by tandem MS experiments utilizing collision induced dissociation (CID) and electron capture dissociation fragmentation techniques
- In CID- MS(2 ), Hex ( 5)HexNAc (4)-N- Asn and HexHexNAc-O-Ser/Thr were typically observed, in agreement with known N-linked biantennary complex-type and O-linked core 1-like structures , respectively
- Additional glycoforms for specific N- and O-linked glycopeptides were also identified, e.g. tetra-antennary N-glycans and fucosylated core 2-like O-glycans.
- Subsequent CID-MS(3), of selected fragment-ions from the CID-MS(2 ) analysis, generated peptide specific b- and y-ions that were used for peptide identification
- In total, 58 N- and 63 O-linked glycopeptides from 53 glycoproteins were characterized with respect to glycan- and peptide sequences
- The combination of CID and electron capture dissociation techniques allowed for the exact identification of Ser/Thr attachment site(s) for 40 of 57 putative O-glycosylation sites
- We defined 29 O-glycosylation sites which have, to our knowledge, not been previously reported
- This is the first study of human urinary glycoproteins where "intact" glycopeptides were studied, i.e. the presence of glycans and their attachment sites were proven without doubt