IDENTIFICATION OF A NOVEL GLYCOSAMINOGLYCAN CORE-LIKE MOLECULE .1. 500 MHZ H-1-NMR ANALYSIS USING A NANO-NMR PROBE INDICATES THE PRESENCE OF A TERMINAL ALPHA-GALNAC RESIDUE CAPPING 4-METHYLUMBELLIFERYL-BETA-D-XYLOSIDES

beta-Xylosides compete with endogenous proteoglycan core proteins and act as alternate accepters for synthesizing protein-free glycosaminoglycan chains, Their assembly on these alternate accepters utilizes the same glycosyltransferases that make the protein-bound chains, Most studies using alternate accepters focus on the production of sulfated glycosaminoglycan chains that are thought to be the major products. However, we previously showed that labeling melanoma cells with [6-H-3]galactose in the presence of 4-methylumbelliferyl (MU) or p-nitrophenyl (pNP) beta-xylosides led to the synthesis of mostly di- to tetrasaccharide products including incomplete core structures, We have solved the structure of one of the previously unidentified products as, GalNAc alpha(1,4)GlcA beta(1,3)Gal beta(1,3)Gal beta(1,4)Xyl beta MU, based on compositional analysis by high performance liquid chromatography, fast atom bombardment, electrospray mass spectrometry, and one dimensional and two dimensional H-1 NMR spectroscopy, The novel aspect of this molecule is the presence of a terminal alpha-Gal-NAc residue at a position that is normally occupied by beta-GalNAc in chondroitin/dermatan sulfate or by alpha-GlcNAc in heparin or heparan sulfate chains. An alpha-GalNAc residue at this critical location may prevent further chain extension or influence the type of chain subsequently added to the common tetrasaccharide core.