Mali M, Jaakkola P, Arvilommi A M, Jalkanen M
Department of Medical Biochemistry, University of Turku, Finland.
J Biol Chem. 1990 Apr 25;265(12):6884-9.
The structure of human syndecan, an integral membrane proteoglycan, has been determined by cloning its full-length cDNA, which codes for the entire 310-amino acid-long core protein, including the NH2-terminal signal peptide. Similar to mouse syndecan (Saunders, S., Jalkanen, M., O'Farrell, S., and Bernfield, M. (1989) J. Cell Biol. 108, 1547-1556), the core protein of human syndecan can be divided into three domains: a matrix-interacting ectodomain containing putative glycosaminoglycan attachment sites, a 25-residue hydrophobic membrane-spanning domain, and a 34-residue cytoplasmic domain. Several interesting conserved structures were revealed by comparing the human syndecan sequence to the murine one. (i) Although the ectodomains are only 70% identical, all putative glycosaminoglycan attachment sites are identical (two of them belong to the consensus sequence SGXG and three others to (E/D)GSG(E/D), as are also (ii) the single putative N-glycosylation site and (iii) the proteinase-sensitive dibasic RK site adjacent to the extracellular face of the transmembrane domain. Furthermore, (iv) the transmembrane domain is 96% identical, as the only change in human syndecan was an alteration of an alanine residue to glycine; and finally, (v) the cytoplasmic domain is 100% identical, including 3 identically located tyrosine residues. Comparison of transmembrane and cytoplasmic domains to a third cell-surface proteoglycan, 48K5 from human lung fibroblasts (Marynen, P., Zhang, J., Cassiman, J., Vanden Berghe, H., and David, C. (1989) J. Biol. Chem. 264, 7017-7024), indicates that the transmembrane and cytoplasmic domains are similar also in this molecule regardless of the presence of a totally nonhomologous ectodomain. Thus, the transmembrane and cytoplasmic domains are unique for these cell-surface proteoglycans, which we propose to be members of a novel gene family of syndecans.
人多配体聚糖（一种整合膜蛋白聚糖）的结构已通过克隆其全长cDNA得以确定，该cDNA编码整个310个氨基酸长的核心蛋白，包括氨基末端信号肽。与小鼠多配体聚糖（桑德斯，S.，亚尔卡宁，M.，奥法雷尔，S.，和伯恩菲尔德，M.（1989年）《细胞生物学杂志》108卷，1547 - 1556页）相似，人多配体聚糖的核心蛋白可分为三个结构域：一个含有假定糖胺聚糖附着位点的与基质相互作用的胞外结构域、一个25个残基的疏水跨膜结构域和一个34个残基的胞质结构域。通过比较人多配体聚糖序列与小鼠序列，发现了几个有趣的保守结构。（i）尽管胞外结构域仅有70%的同源性，但所有假定的糖胺聚糖附着位点都是相同的（其中两个属于共有序列SGXG，另外三个属于（E/D）GSG（E/D）），同样（ii）单一的假定N - 糖基化位点和（iii）跨膜结构域细胞外表面附近的蛋白酶敏感双碱性RK位点也是如此。此外，（iv）跨膜结构域有96%的同源性，因为人多配体聚糖中唯一的变化是一个丙氨酸残基变为了甘氨酸；最后，（v）胞质结构域100%同源，包括3个位置相同的酪氨酸残基。将跨膜结构域和胞质结构域与人肺成纤维细胞的第三种细胞表面蛋白聚糖48K5（马里嫩，P.，张，J.，卡西曼，J.，范登伯格，H.，和大卫，C.（1989年）《生物化学杂志》264卷，7017 - 7024页）进行比较，表明该分子中的跨膜结构域和胞质结构域也相似，尽管存在一个完全非同源的胞外结构域。因此，跨膜结构域和胞质结构域对于这些细胞表面蛋白聚糖来说是独特的，我们认为它们是多配体聚糖新基因家族的成员。
