Syndecans

Syndecans are single transmembrane domain proteins that are thought to act as coreceptors, especially for G protein-coupled receptors. These core proteins carry three to five heparan sulfate and chondroitin sulfate chains which allow for interaction with a large variety of ligands including fibroblast growth factors, vascular endothelial growth factor, transforming growth factor-beta, fibronectin and antithrombin-1. Interactions between fibronectin and some syndecans can be modulated by the extracellular matrix protein tenascin-C.

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Family members

The syndecan protein family is comprised of four members. Syndecans 1 and 3 and syndecans 2 and 4 making up separate subfamilies having arisen by gene duplication and divergent evolution from a single ancestral gene.^[1] The syndecan numbers reflect the order in which the cDNAs for each family member were cloned. All syndecans have an N-terminal signal peptide, an ectodomain, a single hydrophobic transmembrane domain, and a short C-terminal cytoplasmic domain.^[2] The ectodomains show the least amount of amino acid sequence conservation, no more than 10-20%, in contrast the transmembrane and cytoplasmic domains share around 60-70% amino acid sequence identity.^[3] The transmembrane domains contain an unusual alanine/glycine sequence motif while the cytoplasmic domain is essentially composed of two regions of conserved amino acid sequence (C1 and C2), separated by a central variable sequence of amino acids that is distinct for each family member (V).

References

1. ^ Carey, D. J. (1997). "Syndecans: multifunctional cell-surface co-receptors". Biochem. J. 327: 1-16. PMID 9355727.
2. ^ Bernfield M, Kokenyesi R. et al (1992). "Biology of syndecans: a family of transmembrane heparan sulfate proteoglycans". Annu. Rev. Cell. Biol. 8: 365-393. PMID 1335744.
3. ^ David, G. (1993). "Integral membrane heparan sulfate proteoglycans". FASEB. J. 7 (11): 1023-1030.