Structural studies on the chondroitinase ABC-resistant sulfated tetrasaccharides isolated from various chondroitin sulfate isomers.

Various commercially available chondroitin sulfates, including an A isomer from whale cartilage, C and D isomers from shark cartilage, and an E isomer from squid cartilage, were exhaustively digested with a commercial highly purified Proteus vulgaris chondroitinase ABC. Gel chromatography of all digests yielded a disaccharide and an oligosaccharide fraction which was resistant to the enzyme digestion and which accounts for 20-31 mol% of the produced total oligosaccharides. Variably sulfated tetrasaccharides were isolated from the oligosaccharide fraction of each chondroitin sulfate isomer by HPLC, then characterized chemically and enzymatically. One disulfated and three trisulfated components were also characterized by 500-MHz one- and two-dimensional 1H NMR spectroscopy. The structures of one tetrasulfated, four trisulfated, and five disulfated tetrasaccharides with the common core structure, alpha-L-delta 4,5HexpA-(1-->3)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpA-(1-->3) -D-GalpNAc, were determined. All isolated tetrasaccharides were resistant to the highly purified enzyme, but susceptible to the conventional, commercial chondroitinase ABC. The former was also inactive towards alpha-L-delta 4,5HexpA-(1-->3)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpA-(1-->3) -D-GalpNAc isolated from chondroitin, beta-D-GlcpA-(1-->3)-beta-D-GlcpNAc-(1-->4)-beta-D-GlcpA-(1- ->3)-D-GlcpNAc from hyaluronan, and alpha-L-delta 4,5HexpA-(1-->3)-beta-D-GalpNAc4SO3(-)-(1-->4)-alpha-L-Id opA-(1-->3)-D- GalpNAc4SO3- from dermatan sulfate. These results indicate that, unlike the conventional enzyme, highly purified chondroitinase ABC cannot degrade tetrasaccharides irrespective of their sulfation profiles. The enzymatic action is size-dependent.