Development and application of strategies for the analysis of modification patterns in chondroitin and dermatan sulphate

Sammanfattning: Chondroitin (CS) and dermatan sulphate (DS) are socalled glycosaminoglycans (GAG) that are covalently attached to various type of proteins forming a subgroup within the diverse proteoglycan (PG) family. The PGs studied in this thesis are mostly extracellularly located and include aggrecan, biglycan and decorin. The CS and DS chains both consist of repeating disaccharides of the type (hexuronic acid-N-acetylgalactosamine)n. The uronic acid is D-glucuronic acid and the galactosamines are sulphated at C-4 or C-6 in CS. In DS, the hexuronic acid can be either D-glucuronic or L-iduronic acid (C-5 epimers). In both cases the GAGs are joined to the protein via the socalled linkage-region sequence D-gluc-/L-iduronic acid-(galactose)2-xylose-serine. In this thesis, methods for sequence analysis of CS/DS were developed and applied. The procedure involves liberation of GAGs from the protein by alkaline scission of the xylose-to-serine bond, coupling of an iodinatable compound to the reducing terminal xylose and radiolabelling of the adduct, partial to complete degradation with specific enzymes which e.g. cleave bonds involving L-iduronic acid or D-glucuronic acid or D-glucuronic acid adjacent to 6-sulphated galactosamine. The products formed are separated by electrophoresis and fragments extending from the tagged reducing end to the point of cleavage are visualized by radio-imaging. By applying this method to CS from aggrecan of various cartilages, it was revealed that there is a non-random distribution of 4- and 6-sulphated N-acetylgalactosamine. In biglycan- and decorin-derived DS a tissue-specific, periodic and wave-like distribution pattern for the two C-5-epimeric uronic acids was demonstrated. The linkage-region of CS and DS were also compared in detail. In CS the trisaccharide sequence (galactose)2-xylose was mostly unsulphated, whereas in DS, sulphate appeared to be obligatory on the second galactose. The results also confirmed the strong connection between 4-sulphation and the presence of L-iduronic acid. By using iodinatable xylosides as primers for CS/DS synthesis in cultured cells, sequence analysis of secreted free GAG-chains was performed. These results demonstrated that the epimerization and sulphation patterns were greatly influenced by the primer concentration. The procedure presented here could be used for sequence analysis of other GAGs, for investigations on the regulation of GAG assembly, i.e. polysaccharide engineering, or for studying GAG-ligand interactions via foot-printing analysis.