Glycogenin belongs the GT 8 family and initiates the biosynthesis of glycogen.
Glycogenin initiates the biosynthesis of glycogen by incorporating glucose residues through a self-glucosylation reaction at a Tyr residue, and then acts as substrate for chain elongation by glycogen synthase and branching enzyme. It contains a conserved DxD motif and an N-terminal beta-alpha-beta Rossmann-like fold that are common to the nucleotide-binding domains of most glycosyltransferases. The DxD motif is essential for coordination of the catalytic divalent cation, most commonly Mn2+. Glycogenin can be classified as a retaining glycosyltransferase, based on the relative anomeric stereochemistry of the substrate and product in the reaction catalyzed. It is placed in glycosyltransferase family 8 which includes lipopolysaccharide glucose and galactose transferases and galactinol synthases.