Synthesis of the glycosaminoglycan-protein linkage tetraosyl peptide moieties of betaglycan, which serve as a hexosamine acceptor for enzymatic glycosyl transfer

Betaglycan, also known as TGF-beta type III receptor, is a membrane-anchored proteoglycan, which has two glycosaminoglycan (GAG) attachment sites (Lopez-Casillas, F.; Payne, H. M.; Andres, J. L.; Massague, J. J. Cell Biol. 1994, 124, 557-568). Chondroitin sulfate (CS) or heparan sulfate (HS) can attach to the first site, Ser(535), whereas only CS attaches to the second, Ser(546). Although the mechanism behind the assembly of CS and HS is not fully understood, it has been reported that the assembly of HS requires not only a cluster of acidic residues but also hydrophobic residues located near the Ser-Gly attachment sites (Esko, J. D. Zhang, L Curr. Opin. Struct. Biol. 1996, 6, 663-670). To further understand the effects of amino acids close to the Ser residues of the GAG-attachment sites on the glycosyltransferases, two tetraosyl peptides derived from the CS attachment sites of betaglycan, GLcA-Gal-Gal-Xyl-SerGlyAspAsnGly (1) and GLcA-Gal-Gal-Xyl-SerGlyAspAsnGlyPheProGly (2), were synthesized, and used as donor substrates for beta 1,4-N-acetylgalactosaminyltransferase-I (alpha 4GaINAcT-I) and alpha 1,4-N-acetylglucosaminyltransferase-I (beta 4GlcNAcT-I). Both the chemically synthesized linkage region tetrasaccharides were far better acceptors for beta 4GalNAcT-I than for alpha 4GlcNAcT-1 in vitro, although they also showed appreciable acceptor activity for alpha 4GlcNAcT-I. (C) 2010 Elsevier Ltd. All rights reserved.