In enzymology, a galactosylgalactosylxylosylprotein 3-beta-glucuronosyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are UDP-glucuronate and 3-beta-D-galactosyl-4-beta-D-galactosyl-O-beta-D-xylosylprotein, whereas its 3 products are UDP, 3-beta-D-glucuronosyl-3-beta-D-galactosyl-4-beta-D-galactosyl-O-, and beta-D-xylosylprotein.
This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases. The systematic name of this enzyme class is UDP-glucuronate:3-beta-D-galactosyl-4-beta-D-galactosyl-O-beta-D-xyl osyl-protein D-glucuronosyltransferase. Other names in common use include glucuronosyltransferase I, and uridine diphosphate glucuronic acid:acceptor glucuronosyltransferase. This enzyme participates in chondroitin sulfate biosynthesis and glycan structures - biosynthesis 1. It employs one cofactor, manganese.
As of late 2007, 4 structures have been solved for this class of enzymes, with PDB accession codes , , , and .