Glycoproteomic Analysis of the Secretome of

Previous proteomics studies have partially unraveled the complexity of endothelial protein secretion but have not investigated glycosylation, a key modification of secreted and membrane proteins for cell communication. In this study, human umbilical vein endothelial cells were kept in serum-free medium before activation by phorbol-12-my-ristate-13 acetate, a commonly used secretagogue that induces exocytosis of endothelial vesicles. In addition to 123 secreted proteins, the secretome was particularly rich in membrane proteins. Glycopeptides were enriched by zwitterionic hydrophilic interaction liquid chromatography resins and were either treated with PNGase F and H2 18O or directly analyzed using a recently developed workflow combining higher-energy C-trap dissociation (HCD) wit