We report a strategy termed Bio-Orthogonal Cell line-specific Tagging of Glycoproteins (BOCTAG). Cells are equipped by transfection with an artificial biosynthetic pathway (mut-AGX1/NahK/Nh-GalNAc-T2) that transforms an alkyne tagged sugar into the corresponding nucleotide-sugar. Only transfected cells incorporate the bioorthogonal sugar into glycoproteins in the presence of non-transfected cells. The incorporation of alkyne-sugar in glycoproteins allows the installation, by copper(I)-catalyzed reaction, of an acid cleavable biotinylated tag. Glycoproteins are enriched using Streptavidin and. after on-bead digestion, glycopeptides are eluted in acid-conditions to be then analysed by mass spectrometry.