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 (PubMed:22223806, PubMed:15752776, PubMed:15661757, PubMed:25279699, PubMed:25279697, PubMed:23125099, PubMed:21987822). Elongates the glucuronyl-beta-1,4-xylose-beta disaccharide primer structure initiated by B4GAT1 by adding repeating units [-3-Xylose-alpha-1,3-GlcA-beta-1-] to produce a heteropolysaccharide (PubMed:22223806, PubMed:25279699, PubMed:25279697, PubMed:25138275, PubMed:32975514, PubMed:23125099). Requires the phosphorylation of core M3 (O-mannosyl trisaccharide) by POMK to elongate the glucuronyl-beta-1,4-xylose-beta disaccharide primer (PubMed:21987822). Plays a key role in skeletal muscle function and regeneration (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+). Optimum pH is 5 for xylosyltransferase activity. Optimum pH is from 5.5 to 8.0 for Beta-1,3-glucuronyltransferase activity. Protein modification; protein glycosylation. Interacts with DAG1 (via the N-terminal domain of alpha-DAG1); the interaction increases binding of DAG1 to laminin (By similarity). Interacts with B4GAT1 (PubMed:19587235). Ubiquitous. Highest expression in heart, brain and skeletal muscle. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. In the C-terminal section; belongs to the glycosyltransferase 49 family. In the N-terminal section; belongs to the glycosyltransferase 8 family. Extended N-terminus. Glycosyltransferase-like protein LARGE1