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.

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.cite journal | author = Carey, D. J. | title = Syndecans: multifunctional cell-surface co-receptors | journal = Biochem. J. | year=1997 | volume=327 | pages=1–16 | pmid = 9355727] 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.cite journal | author =Bernfield M, Kokenyesi R. "et al" | title = Biology of syndecans: a family of transmembrane heparan sulfate proteoglycans | journal=Annu. Rev. Cell. Biol. | year=1992 | volume=8 | pages=365–393 | pmid = 1335744 | doi = 10.1146/annurev.cb.08.110192.002053] The ectodomains show the least amount of amino acid sequence conservation, not more than 10-20%, in contrast the transmembrane and cytoplasmic domains share around 60-70% amino acid sequence identity.cite journal | author =David, G. | title = Integral membrane heparan sulfate proteoglycans | journal=FASEB. J. | year=1993 | volume=7 | issue=11 | pages=1023–1030 | url=http://www.fasebj.org/cgi/content/abstract/7/11/1023 | pmid = 8370471] 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