Recombinant Human Glypican 5 Protein

The Glypicans (glypiated proteoglycans) are a small multigene family of GPI-linked proteoglycans that likely play a key role in embryonic morphogenesis (1 - 4). There are currently six known mammalian Glypicans. They all share a common-sized protein core of 60 - 70 kDa, an N-terminus which likely forms a compact globular domain, 14 conserved cysteines that form multiple intrachain disulfide bonds, and a number of C-terminal N- and O-linked carbohydrate attachment sites. Based on exon organization and the location of O-linked glycosylation sites, at least two subfamilies of glypicans are known, with one subfamily containing Glypicans-1, 2, 4 and 6, and another subfamily containing Glypicans-3 and 5 (3, 5). Human Glypican-5 (GPC-5) is synthesized as a 572 amino acid (aa) preproprecursor that contains a 24 aa signal sequence, a 532 aa mature region and a 16 aa C-terminal prosegment (6, 7). There are three potential N-linked, and five potential O-linked sites for glycosylation or glycanation. GPC-5 is believed to contain 6 - 7 kDa of glycosylation and at least 55 kDa of proteoglycan. This is based on an assumption of the presence of one heparan sulfate chain of 36 kDa and one chrondroitin sulfate chain of 17 kDa (7, 8). When added to the core molecular weight of 59 kDa, the mature protein is approximately 120 kDa in size. To date, however, the actual size of native human GPC-5 has not been reported and the suggestion of a chrondroitin sulfate modification is based on the expression of human GPC-5 in COS-7 cells (7). Human to mouse, there is 88% aa identity over the mature region. Cells known to express GPC-5 are principally embryonic in nature, and include neurons and mesenchyme (1, 7). The function of GPC-5 is essentially unknown. As a glypican family member, it may facilitate heparin-binding growth factor signaling and polyamine uptake into expressing cells (9, 10).