Sequence of human syndecan indicates a novel gene family of integral membrane proteoglycans.
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.
Mali
M
M
Department of Medical Biochemistry, University of Turku, Finland.
Jaakkola
P
P
Arvilommi
A M
AM
Jalkanen
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D001940:Breast; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D005260:Female; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D011509:Proteoglycans / Q000235:genetics*; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D053667:Syndecans
D008562:Membrane Glycoproteins; D011509:Proteoglycans; D053667:Syndecans; D004247:DNA