MOD_GlcNHglycan

Proteoglycans are found at the cell surface and in the extracellular matrix. They are important for cell communication, playing a role for example in morphogenesis and development. Mutations in some proteoglycans are associated with an inherited predisposition to cancer. The core protein is modified by attachment of the glycosaminoglycan chain at an exposed serine residue. For heparan sulphate, the process begins by transfer of xylose from UDP-xylose to the serine hydroxyl group by protein xylosyl transferase (EC 2.4.2.26) in the Golgi stack. The system appears to have evolved in metazoan animals.