xylosyltransferases

Xylosyltransferases are enzymes that catalyze the transfer of a xylose residue from UDP-xylose to serine residues on specific proteins, initiating the synthesis of proteoglycans. This initial xylose addition forms the first sugar of the common proteoglycan linkage region, which is followed by the sequential addition of galactose, galactose, and glucuronic acid to complete the Ser-Gly-X-Gly linkage that anchors glycosaminoglycan chains.

In humans and many vertebrates, two related enzymes, XYLT1 and XYLT2, encode xylosyltransferases I and II, respectively. These Golgi-localized glycosyltransferases use UDP-xylose as donor and serine on proteoglycan core proteins as acceptor. Their activity initiates the biosynthesis of proteoglycans, which are major components of the extracellular matrix and play key roles in tissue structure, filtration, and signaling.

The function of xylosyltransferases is critical for proper proteoglycan assembly and for the formation of the characteristic linkage region that enables subsequent elongation of glycosaminoglycan chains. While best understood in the context of proteoglycans, xylosyltransferases are considered part of a broader family of glycosyltransferases involved in diverse xylose-transfer reactions across different organisms and substrates.

Overall, xylosyltransferases initiate a foundational step in glycoprotein and extracellular matrix biosynthesis, with XYLT1 and XYLT2 representing the principal enzymes characterized in humans.