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 glycosaminogl ycan chains, Their assembly on these alternate accepters utilizes the same glycosyltransferases that make the protein-bound chains, Most stu dies using alternate accepters focus on the production of sulfated gly cosaminoglycan chains that are thought to be the major products. Howev er, we previously showed that labeling melanoma cells with [6-H-3]gala ctose in the presence of 4-methylumbelliferyl (MU) or p-nitrophenyl (p NP) beta-xylosides led to the synthesis of mostly di- to tetrasacchari de products including incomplete core structures, We have solved the s tructure of one of the previously unidentified products as, GalNAc alp ha(1,4)GlcA beta(1,3)Gal beta(1,3)Gal beta(1,4)Xyl beta MU, based on c ompositional 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 mol ecule is the presence of a terminal alpha-Gal-NAc residue at a positio n that is normally occupied by beta-GalNAc in chondroitin/dermatan sul fate or by alpha-GlcNAc in heparin or heparan sulfate chains. An alpha -GalNAc residue at this critical location may prevent further chain ex tension or influence the type of chain subsequently added to the commo n tetrasaccharide core.