Catalyzes the first step in the biosynthesis of chondroitin sulfate, heparan sulfate and dermatan sulfate proteoglycans, such as DCN. Transfers D-xylose from UDP-D-xylose to specific serine residues of the core protein. L-seryl-[protein] + UDP-alpha-D-xylose = 3-O-(beta-D-xylosyl)-L-seryl-[protein] + H(+) + UDP Active with either Mg(2+) or Mn(2+), but activity is highest when both are present. Glycan metabolism; chondroitin sulfate biosynthesis. Glycan metabolism; heparan sulfate biosynthesis. Monomer. Widely expressed. Expressed at higher level in kidney and pancreas. Contains disulfide bonds. The disease is caused by variants affecting the gene represented in this entry. The gene represented in this entry acts as a disease modifier. PXE patients carrying causative ABCC6 mutations, manifest a more severe disease course characterized by earlier onset, frequent skin lesions and higher organ involvement, in the presence of XYLT2 variants. Belongs to the glycosyltransferase 14 family. XylT subfamily.