Phosphorylation of proteoglycans. Identification of phosphorylation sites in chondroitin sulfate-rich region of core protein.
Serine residues, which are the sites of phosphorylation in proteoglycans, were demonstrated to be located on chondroitin sulfate-containing peptides. These peptides appeared to be derived primarily from the chondroitin sulfate-rich region of the proteoglycan core protein. The localization of phosphate moieties in the chondroitin sulfate-containing peptides was observed in all experiments. The phosphate moieties were retained on chondroitin sulfate-containing peptides after the protein core was treated with either papain or trypsin. Two phosphopeptide preparations, derived from chondroitin sulfate-containing peptides of proteoglycan subunits, were extensively purified. These 2 phosphopeptide preparations were shown by carbohydrate analysis to be free of keratan sulfate-containing peptides or peptides from the hyaluronic acid binding region of the core protein. One of the phosphopeptide preparations had a phosphate: serine molar ratio of 0.40. This indicated that nearly one-half of the serine residues were phosphorylated rather than glycosylated. Peptides derived from the core protein that contained keratan sulfate had no phosphate moieties.
D002358:Cartilage, Articular / Q000378:metabolism*; D002807:Chondroitin / Q000031:analogs & derivatives*; D002809:Chondroitin Sulfates / Q000378:metabolism*; D006801:Humans; D010455:Peptides / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D010748:Phosphopeptides / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011509:Proteoglycans / Q000378:metabolism*; D012694:Serine / Q000378:metabolism
D010455:Peptides; D010710:Phosphates; D010748:Phosphopeptides; D011509:Proteoglycans; D010768:Phosphoserine; D012694:Serine; D002807:Chondroitin; D002809:Chondroitin Sulfates