ABSTRACT
The name glypican identifies a family of heparan sulfate proteoglycans (HSPGs) that are linked to the exocytoplasmic surface of the plasma membrane through a covalent glycosyl-phosphatidylinositol (GPI) anchor (1). Proteins anchored in this manner are said to be ‘‘glypiated’’ (2). The possible existence of a distinct population of glypiated cell surface HSPGs (as opposed to the transmembrane HSPGs or those peripherally associated) was recognized about a decade ago (3,4). These initial experiments showed that a fraction of the cell surface HSPGs could be released by treating the cells with phosphatidylinositol-specific phospholipase C (PI-PLC). Although alternative explanations could be given for the presence of such phospholipase C-labile proteoglycans (e.g., a glypiated isoform of a transmembrane proteoglycan), the subsequent cloning and characterization of a protein with its own discrete open reading frame left no doubts as to the distinctiveness of this population of glypiated HSPGs (5).
