Galactosylgalactosylxylosylprotein 3-beta-glucuronosyltransferase 1 is a member of the glucuronyltransferase gene family. These enzymes exhibit strict acceptor specificity, recognizing nonreducing terminal sugars and their anomeric linkages. This gene product functions as the key enzyme in a glucuronyl transfer reaction during the biosynthesis of the carbohydrate epitope HNK-1 (human natural killer-1, also known as CD57 and LEU7).

Alternate transcriptional splice variants have been characterized.In immunology, the CD57 antigen (CD stands for cluster of differentiation) is a protein which is also called HNK1 (human natural killer-1) or LEU7. It is a neuronally expressed adhesion molecule with a carbohydrate epitope that contains a sulfoglucuronyl residue.