In multicellular organisms, there are three types of protein glycosylation. N-glycosylation, O-mannosylation and C-mannosylation. All of these processes take place in the endoplasmic reticulum, and in all of them enzymes attach sugar residues to specific sites in newly forming protein.
Click here for original story, A breakthrough in understanding the sugar biology of multicellular organisms
Source: Phys.org