Bifunctional glycosyltransferase with both alpha-1,3-xylosyltransferase and beta-1,3-glucuronyltransferase activities involved in the maturation of alpha-dystroglycan (DAG1) by glycosylation leading to DAG1 binding to laminin G-like domain-containing extracellular proteins with high affinity and in a phosphorylated-O-mannosyl trisaccharide dependent manner. Elongates the glucuronyl-beta-1,4-xylose-beta disaccharide primer structure by adding repeating units [-3-Xylose-alpha-1,3-GlcA-beta-1-] to produce a heteropolysaccharide (By similarity). Supports the maturation of DAG1 more effectively than LARGE1 (By similarity). In addition, can modify both heparan sulfate (HS)- and chondroitin/dermatan sulfate (CS/DS)-proteoglycans (PGs), namely GPC4, with a glycosaminoglycan (GAG)-like polysaccharide composed of xylose and glucuronic acid to confer laminin binding (By similarity). 3-O-[beta-D-GlcA-(1->3)-beta-D-Xyl-(1->4)-Rib-ol-P-Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-(O-6-P-alpha-D-Man)]-Thr-[protein] + UDP-alpha-D-xylose = 3-O-[alpha-D-Xyl-(1->3)-beta-D-GlcA-(1->4)-beta-D-Xyl-(1->4)-Rib-ol-P-Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-(O-6-P-alpha-D-Man)]-Thr-[protein] + H(+) + UDP 3-O-{(1->[3)-alpha-D-Xyl-(1->3)-beta-D-GlcA-(1->](n)-4)-beta-D-Xyl-(1->4)-Rib-ol-P-Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-O-6-P-alpha-D-Man}-L-Thr-[protein] + UDP-alpha-D-glucuronate = 3-O-{beta-D-GlcA-(1->[3)-alpha-D-Xyl-(1->3)-beta-D-GlcA-(1->](n)-4)-beta-D-Xyl-(1->4)-Rib-ol-P-Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-O-6-P-alpha-D-Man}-L-Thr-[protein] + H(+) + UDP 3-O-{beta-D-GlcA-(1->[3)-alpha-D-Xyl-(1->3)-beta-D-GlcA-(1->](n)-4)-beta-D-Xyl-(1->4)-Rib-ol-P-Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-O-6-P-alpha-D-Man}-L-Thr-[protein] + UDP-alpha-D-xylose = 3-O-{(1->[3)-alpha-D-Xyl-(1->3)-beta-D-GlcA-(1->](n+1)-4)-beta-D-Xyl-(1->4)-Rib-ol-P-Rib-ol-P-3-beta-D-GalNAc-(1->3)-beta-D-GlcNAc-(1->4)-O-6-P-alpha-D-Man}-L-Thr-[protein] + H(+) + UDP Binds 2 Mn(2+) ions per subunit. The xylosyltransferase part binds one Mn(2+) and the beta-1,3-glucuronyltransferase part binds one Mn(2+). Protein modification; protein glycosylation. In the C-terminal section; belongs to the glycosyltransferase 49 family. In the N-terminal section; belongs to the glycosyltransferase 8 family.