Researcher:
Ruedi Aebersold, professor of molecular systems biology, Swiss Federal Institute of Technology, Zurich
Project:
Cancer biomarker discovery in serum
Problem:
If most proteins are glycosylated, most peptides are not. Thus, a whole-cell or whole-serum protein extract can overwhelm a mass spectrometer. Aebersold needed a way to focus only on glycosylated fragments.
Solution:
Aebersold enriched his samples with a method called solid-phase extraction of N-linked glycopeptides ( Nat Protocols, 2:334-9, 2007). A protein extract is digested to peptides, and treated with sodium periodate to oxidize the sugars to aldehydes. These activated sugars are then chemically coupled to hydrazide beads, while unmodified peptides are washed away. Finally, the peptides are cleaved from the resin using protein N-glycanase (PNGase)-F, leaving the glycan groups, and are sequenced via tandem mass spec.
Whereas a typical protein may yield 100 or so tryptic peptides, "Typically, a glycoprotein treated in this way will produce three to ...
