| 1. |
- de Luca, S., et al.
(författare)
-
Proteoglycans from chick limb bud chondrocyte cultures. Keratan sulfate and oligosaccharides which contain mannose and sialic acid
- 1980
-
Ingår i: Journal of Biological Chemistry. - 0021-9258. ; 255:13, s. 6077-6083
-
Tidskriftsartikel (refereegranskat)abstract
- The precursors, [ 35S]sulfate and [2- 3H]mannose, were used to study the biosynthesis of keratan sulfate and other oligosaccharides on proteoglycans isolated from Day 8 cultures of chick limb bud chondrocytes. After alkaline borohydride treatment, three fractions with sialic acid were separated by molecular sieve chromatography. The first contained keratan sulfate which was purified by digestion with chondroitinase to remove chondroitin sulfate, followed by molecular sieve and ion exchange chromatography. The purified keratan sulfate contained about 8% of the 35S activity originally in monomer. The chains had an average length of about 40 monosaccharides and contained only trace amounts of mannose (less than 1 residue/three to four chains). The second fraction contained the majority of the [ 3H]mannose originally in monomer, but no 35S activity. This fraction appears to contain oligosaccharide-peptides of the asparagine-N-glycosylamine type because there were no reduced sugars present and the alkaline borohydride treatment extensively degraded the core protein. The composition of the oligosaccharides, with high proportions of mannose, N-acetylglucosamine, galactose, and sialic acid, was consistent with this suggestion. The third fraction consisted of a series of oligosaccharides with sizes between three to six saccharides. They contained N-acetylgalactosaminitol, indicating that they were attached to the core protein by O-glycoside bonds between N-acetylgalactosamine and hydroxyl groups on serine and threonine. Thus, proteoglycans contain two classes of oligosaccharides, a mannose-rich class characteristic of glycoproteins and an O-glycoside class characteristic of mucins, in addition to the chondroitin sulfate and keratan sulfate chains.
|
|
| 2. |
- Lohmander, Stefan, et al.
(författare)
-
Formation of proteoglycan aggregates in rat chondrosarcoma chondrocyte cultures treated with tunicamycin
- 1983
-
Ingår i: Journal of Biological Chemistry. - 0021-9258. ; 258:20, s. 12280-12286
-
Tidskriftsartikel (refereegranskat)abstract
- Proteoglycan monomer and link protein isolated from the Swarm rat chondrosarcoma both contain glycosylamine-linked oligosaccharides. In monomer, these N-linked oligosaccharides are concentrated in a region of the protein core which interacts specifically with both hyaluronate and link protein to form proteoglycan aggregates present in the cartilage matrix. Chondrocyte cultures were treated with tunicamycin to inhibit synthesis of the N-linked oligosaccharides, and the ability of the deficient proteoglycan and link protein to form aggregates was studied. Cultures were pretreated with tunicamycin for 3 h and then labeled with either [3H]mannose, [3H]glucosamine, [3H]serine, or with [35S]sulfate for 6 h in the presence of tunicamycin. Formation of link protein-stabilized proteoglycan aggregates in the culture medium was inhibited by up to 40% when the cells were treated with 3 μg of tunicamycin/ml, a concentration which inhibited 3H incorporation with mannose as a precursor by about 90%, but by only 15% with glucosamine as a precursor. When exogenous proteoglycan aggregate was added to the culture medium, however, it was found that both endogenous monomer and link protein synthesized in the presence of tunicamycin were fully able to form link-stabilized aggregates. This suggests that glycosylamine-linked oligosaccharides on monomer and on link protein are not necessary for their specific interactions with hyaluronate and with each other. Further, although tunicamycin did not inhibit net synthesis of hyaluronate, transfer of hyaluronate from the cell layer to the culture medium was retarded. This phenomenon accounted for most if not all of the decrease in the amount of proteoglycan which formed aggregates in the medium of cultures treated with tunicamycin.
|
|
| 3. |
|
|
| 4. |
- Thonar, E. J M A, et al.
(författare)
-
Biosynthesis of O-linked oligosaccharides on proteoglycans by chondrocytes from the swarm rat chondrosarcoma
- 1983
-
Ingår i: Journal of Biological Chemistry. - 0021-9258. ; 258:19, s. 11564-11570
-
Tidskriftsartikel (refereegranskat)abstract
- The core protein of proteoglycans from cartilage is substituted with glycosaminoglycans as well as N- and O-glycosidically linked oligosaccharides. We have taken advantage of the long intracellular half-life of the core protein precursor to the rat chondrosarcma proteoglycan to study the temporal relationship between the addition of the chondroitin sulfate chains and the O-linked oligosaccharides onto the core protein during the formation of the completed proteoglycan molecule. Chondrocyte cultures were pulsed on day 2 with [6-3H]glucosamine for times ranging from 30-420 min. Media and corresponding 4% zwittergent, 4 M guanidine HCl extracts were then pooled and subjected to dissociative density gradient ultracentrifugation to yield purified proteoglycan monomers which were then subjected to alkaline borohydride treatment. The released chondroitin sulfate chains were then purified by precipitation with 50% (v/v) ethanol. The O-linked oligosaccharide-alditols in the supernatant fractions were purified by molecular sieve chromatography on Bio-Gel P-6, and analyzed after digestion with α-neuraminidase and subsequent chromatography on Bio-Gel P-2. The different O-linked oligosaccharide-alditols were identified from their hexosamine and hexosaminitol contents. The kinetics of entry of 3H label into N-acetylgalactosamine of chondroitin sulfate was indistinguishable from that into either N-acetylglucosamine or N-acetylgalactosaminitol residues of the oligosaccharide-alditols, with half-times to linear incorporation of 10-17 min. These results show that initiation as well as completion of the O-linked oligosaccharides on the core protein occurs essentially at the same time that chondroitin sulfate chains are added. The results suggest that these biosynthetic processes occur in the Golgi apparatus during the last few minutes of the total intracellular dwell time (half-time of about 90 min) of the core protein acceptor.
|
|
