Biosynthesis of the proteoglycan decorin--transient 2-phosphorylation of xylose during formation of the trisaccharide linkage region.
Phosphorylation of decorin was investigated by incubating a rat fibroblast cell line with radiolabelled phosphate and carbohydrate precursors. There was a transient phosphorylation of the linkage-region saccharides in intracellular decorin prior to assembly of the galactosaminoglycan chain. Phosphorylation gradually increased from xylosylated, galactosyl-xylosylated to galactosyl-galactosyl-xylosylated core protein where all trisaccharide stubs were phosphorylated. Addition of the first glucuronate residue was accompanied by rapid dephosphorylation. Brefeldin A treatment resulted in segregation of galactosaminoglycan synthesis and dephosphorylation. Enzymatic degradation of brefeldin-A-arrested immature proteoglycan with incomplete galactosaminoglycan chain [Moses, J., Oldberg, A., Eklund, E. & Fransson, L.-A. (1997) Eur. J. Biochem., in the press] by using chondroitin AC lyase and chondro-glycuronidase, followed by beta-galactosidase treatment, demonstrated the sequence galactosyl-galactosyl-phosphoxylose. The xylose was resistant to direct periodate oxidation, but sensitive after treatment with alkaline phosphatase, showing that the phosphate was located at C2 of xylose. The transient 2-phosphorylation of xylose may be involved in intracellular transport and/or in the control of modifications of the glycan chain.
Moses
J
J
Department of Cell and Molecular Biology, Faculties of Odontology, Lund University, Sweden. jonatan.moses@medkem.lu.se
Oldberg
A
A
Cheng
F
F
Fransson
L A
LA
D000818:Animals; D020126:Brefeldin A; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D019765:Chondroitin ABC Lyase / Q000378:metabolism; D003517:Cyclopentanes / Q000494:pharmacology; D058575:Decorin; D016326:Extracellular Matrix Proteins; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005944:Glucosamine / Q000378:metabolism; D005965:Glucuronates / Q000378:metabolism; D020723:Glucuronic Acid; D005966:Glucuronidase / Q000378:metabolism; D008969:Molecular Sequence Data; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011509:Proteoglycans / Q000096:biosynthesis* / Q000737:chemistry; D051381:Rats; D014312:Trisaccharides / Q000737:chemistry / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism*
D003517:Cyclopentanes; C546880:Dcn protein, rat; D058575:Decorin; D016326:Extracellular Matrix Proteins; D005965:Glucuronates; D010710:Phosphates; D011500:Protein Synthesis Inhibitors; D011509:Proteoglycans; D014312:Trisaccharides; D020126:Brefeldin A; D020723:Glucuronic Acid; D014994:Xylose; D005966:Glucuronidase; D019765:Chondroitin ABC Lyase; D005944:Glucosamine; D005690:Galactose