Figure 1.

Schematic overview of coreceptor functions of cell surface heparan sulfate proteoglycans (HSPGs) I. A: interaction with soluble ligands: cell surface HSPGs capture soluble ligands, increase their local concentration, and increase their availability for signaling receptors. B: interaction with extracellular matrix (ECM) components: cell surface HSPG binding facilitates binding of ECM components to integrin receptors in a heparan sulfate (HS)-dependent manner. C: formation of ligand/receptor/HSPG complexes: cell surface HSPGs bind to both ligands and signaling receptors to form a tertiary receptor complex. D: oligomerization of ligands: cell surface HSPGs provide a HS platform with multiple binding sites for ligand oligomerization, and ligand oligomers interact more avidly with signaling receptors.