In nucleotide sugar metabolism a group of biochemicals known as nucleotide sugars act as donors for sugar residues in the glycosylation reactions that produce polysaccharides.^[1] They are substrates for glycosyltransferases.^[2] The nucleotide sugars are also intermediates in nucleotide sugar interconversions that produce some of the activated sugars needed for glycosylation reactions.^[1] Since most glycosylation takes place in the endoplasmic reticulum and golgi apparatus, there are a large family of nucleotide sugar transporters that allow nucleotide sugars to move from the cytoplasm, where they are produced, into the organelles where they are consumed.^[3][4]

Nucleotide sugar metabolism is particularly well-studied in yeast,^[5] fungal pathogens,^[6] and bacterial pathogens, such as E. coli and Mycobacterium tuberculosis, since these molecules are required for the synthesis of glycoconjugates on the surfaces of these organisms.^[7][8] These glycoconjugates are virulence factors and components of the fungal and bacterial cell wall. These pathways are also studied in plants, but here the enzymes involved are less well understood.^[9]