Recombinant Mouse 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 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). Mouse glypican-5 (GPC-5) is synthesized as a 572 amino acid (aa) preproprecursor that contains a 24 aa signal sequence and, based on human GPC-5, a 532 aa mature segment plus a 16 aa C-terminal prosegment (6, 7). There are four potential N-linked, and four 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 the least one heparan sulfate chain of 36 kDa and one chrondroitin sulfate chain of 17 kDa (8, 9). When added to the core molecular weight of 59 kDa, it may be approximately 120 kDa in the native state. The actual size of neither mouse nor human GPC-5 has been reported, and the suggestion of a chrondroitin sulfate modification is based on the expression of human GPC-5 in COS-7 cells (8). Mouse to human, 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, 8). As a glypican family member, it may facilitate heparin-binding growth factor signaling and polyamine uptake into expressing cells (10, 11).