Heparan sulfate (HS) is a glycosaminoglycan that plays a critical role in numerous cellular processes. It is a key component of proteoglycans located on cell surfaces and within extracellular matrices, where it influences development, cell signaling, and the progression of various diseases.

Structure

Heparan sulfate consists of repeating disaccharide units composed of a uronic acid (either glucuronic acid or iduronic acid) and a glucosamine residue. These units undergo extensive modifications, including sulfation and epimerization, generating distinct domains with variable sulfation patterns. This structural heterogeneity enables specific interactions with a wide range of proteins. HS biosynthesis occurs in a non-template-driven manner and is mediated by sulfotransferases and epimerases.

Biosynthesis

HS chains are assembled on core proteins through initiation by xylosyltransferase, followed by chain polymerization and a series of modification steps. These include N-deacetylation and N-sulfation, C5-epimerization of glucuronic acid to iduronic acid, and O-sulfation at the 2-, 6-, and 3-positions. Enzymes such as NDST, HS2ST, HS6ST, and HS3ST regulate the formation of sulfated domains, resulting in tissue-specific and developmentally regulated HS structures.

Functions

Heparan sulfate binds a wide array of growth factors, cytokines, and cell surface receptors, thereby modulating signaling pathways involved in development, angiogenesis, and tissue homeostasis. It plays a key role in regulating embryonic stem cell fate and mediating interactions between host cells and pathogens. The specificity of these interactions is largely dictated by the sulfation patterns within HS chains.