Xylosyltransferase I, II (XYLT1,2)

Abstract

Proteoglycans (PGs) impact many fundamental biological processes, including cytokine and growth factor function, morphogen gradient formation, co-receptor activity, and basement membrane homeostasis. All cells produce PGs. These glycoconjugates are cell surface associated, stored in intracellular granules, or secreted into the extracellular space. Although cells can survive without the assembly of glycosaminoglycan chains (GAGs) on core proteins (Esko et al. 1985), multicellular organization and subsequent differentiation in processes such as gastrulation are entirely dependent on PGs (Lin et al. 2000). This highlights the significant role that PGs have in intercellular communications. The addition of xylose is thought rate limiting for GAG chain assembly on the core protein. Not all core proteins are consistently modified, and these molecules are referred to as part-time PGs (Fig. 40.1).