N-Linked glycan diversity in Drosophila and other insects. N-Linked glycan processing after endoplasmic reticulum (ER) mannosidase trimming to the Man₅GlcNAc₂ structure is shown. (Gray boxes) The predominant N-linked glycans, Man₅GlcNAc₂ and Man₃GlcNAc₂Fuc, are found in all stages of Drosophila. N-linked glycan complexity is limited by the Fdl hexosaminidase and expanded by expression of uncharacterized branching N-acetylglucosaminyltransferase activities, undefined galactosyl-, N-acetylgalactosaminyl-, and glucuronosyl-transferase activities, and a single identified sialyltransferase activity. Core fucosylation occurs at C-6 and/or at C-3 of the reducing terminal N-acetylglucosamine residue, catalyzed by FucT6 or FucTA, respectively. Fucosylation at C-3 generates the neural-specific horseradish peroxidase (HRP) epitope. Sulfation of the α1-6-linked core mannose (Man) residue has been detected on all N-linked glycan classes except sialylated glycans in Drosophila and other insects.