sugars are added to proteins to form glycoprotein in granules.
where are sugars added to proteins to form glycoprotein?
granules
bullet::::- polyglutamylation, covalent linkage of glutamic acid residues to the n-terminus of tubulin and some other proteins. (see tubulin polyglutamylase)





























bullet::::- polyglycylation, covalent linkage of one to more than 40 glycine residues to the tubulin c-terminal tail





























bullet::::- butyrylation





























bullet::::- gamma-carboxylation dependent on vitamin k





























bullet::::- glycosylation, the addition of a glycosyl group to either arginine, asparagine, cysteine, hydroxylysine, serine, threonine, tyrosine, or tryptophan resulting in a glycoprotein. distinct from glycation, which is regarded as a nonenzymatic attachment of sugars.





























bullet::::- polysialylation, addition of polysialic acid, psa, to ncam





























bullet::::- malonylation
post-translational modification
addition of n-acetylgalactosamine (galnac) to a serine or threonine occurs in the golgi apparatus, after the protein has been folded. the process is performed by enzymes known as galnac transferases (galnts), of which there are 20 different types. the initial "o"-galnac structure can be modified by the addition of other sugars, or other compounds such as methyl and acetyl groups. these modifications produce 8 core structures known to date. different cells have different enzymes that can add further sugars, known as glycosyltransferases, and structures therefore change from cell to cell. common sugars added include galactose, n-acetylglucosamine, fucose and sialic acid. these sugars can also be modified by the addition of sulfates or acetyl groups.
o-linked glycosylation