Biosynthesis and processing of proteodermatan sulphate

The biosynthesis and processing of the small iduronic acid-rich proteodermatan sulphate (PDS) was studied in cultured human skin fibroblasts and arterial smooth muscle cells (SMC) with the aid of core-directed antibodies and various inhibitors of protein synthesis, intracellular transport, and glycosylation. Components of the linkage region became attached to the core protein most likely in a pre-Golgi compartment. Phosphorylation of PDS precursors also occurred in the endoplasmic reticulum with a minor contribution by the Golgi complex. Serine residues and the linkage region were identified as phosphorylated species in secreted PDS. Blockade of transport by monensin did not affect 6-sulphation but affected uronic acid epimerization and 4-sulphation. On relief from the monensin block, additional sulphation along the glycosaminoglycan chain was possible, whereas chain elongation was as in the continuous presence of the drug. Asparagine-bound oligosaccharides or glycosaminoglycan chains were not required for secretion of PDS or core protein. PDS from fibroblast and SMC secretions differed markedly in the composition of the glycosaminoglycan chains. No significant difference, however, was found on isoelectric focusing of core protein and after limited proteolysis of chondroitin ABC lyase-treated core protein. Tryptic and chymotryptic peptide maps of iodinated core proteins were similar.