Kimura J H, Lohmander L S, Hascall V C
J Cell Biochem. 1984;26(4):261-78. doi: 10.1002/jcb.240260406.
Biosynthesis of cartilage proteoglycan was examined in a model system of cultured chondrocytes from a transplantable rat chondrosarcoma. Extensive modification with the addition of chondroitin sulfate glycosaminoglycan, N-linked oligosaccharide, and O-linked oligosaccharide is required to convert a newly synthesized core protein precursor into a proteoglycan. Kinetic analyses revealed the presence of a large pool of core protein precursor (t 1/2 approximately 90 min) awaiting completion into proteoglycan. The large t 1/2 of this pool allowed kinetic labeling experiments with a variety of radioactive precursors to distinguish between early biosynthetic events associated primarily with the rough endoplasmic reticulum from late events associated primarily with the Golgi apparatus. The results of a series of experiments indicated that the addition of N-linked oligosaccharide chains occurs early in the biosynthetic process in association with the rough endoplasmic reticulum, whereas the initiation and completion of O-linked oligosaccharides occurs much later, at about the same time as chondroitin sulfate synthesis. This also indicated that keratan sulfate chains, when present in the completed molecule, are added in the Golgi apparatus, as they are probably built on oligosaccharide primers closely related to the O-oligosaccharide chains. Furthermore, when 3H-glucose was used as the precursor, the entry of label into xylose, the linkage sugar between the core protein and the chondroitin sulfate chain, was found to occur within 5 min of the entry of label into galactose and galactosamine in the remainder of the chondroitin sulfate chain. This indicated that the initiation and completion of the chondroitin sulfate chain occurs late in the pathway probably entirely in the Golgi apparatus. Thus, proteoglycan synthesis can be described as occurring in two stages in this system, translation and N-glycosylation of a core protein precursor which has a long half-life in the rough endoplasmic reticulum, followed by extensive rapid modification in the Golgi complex in which the majority of glycosaminoglycan and oligosaccharide chains are added to the core protein precursor with subsequent rapid secretion into the extracellular matrix.
在一个可移植大鼠软骨肉瘤培养软骨细胞的模型系统中，对软骨蛋白聚糖的生物合成进行了研究。需要添加硫酸软骨素糖胺聚糖、N-连接寡糖和O-连接寡糖进行广泛修饰，才能将新合成的核心蛋白前体转化为蛋白聚糖。动力学分析显示存在大量核心蛋白前体库（半衰期约90分钟），等待完成转化为蛋白聚糖。这个库的长半衰期使得用各种放射性前体进行动力学标记实验能够区分主要与糙面内质网相关的早期生物合成事件和主要与高尔基体相关的晚期事件。一系列实验结果表明，N-连接寡糖链的添加发生在生物合成过程的早期，与糙面内质网相关，而O-连接寡糖的起始和完成则发生得晚得多，与硫酸软骨素合成大约同时发生。这也表明，当硫酸角质素链存在于完整分子中时，是在高尔基体中添加的，因为它们可能是在与O-寡糖链密切相关的寡糖引物上构建的。此外，当使用3H-葡萄糖作为前体时，发现标记物进入木糖（核心蛋白与硫酸软骨素链之间的连接糖）的时间在标记物进入硫酸软骨素链其余部分的半乳糖和半乳糖胺之后5分钟内。这表明硫酸软骨素链的起始和完成发生在该途径的后期，可能完全在高尔基体中。因此，在这个系统中，蛋白聚糖的合成可以描述为分两个阶段进行，即核心蛋白前体的翻译和N-糖基化，该前体在糙面内质网中有较长的半衰期，随后在高尔基体复合体中进行广泛的快速修饰，其中大部分糖胺聚糖和寡糖链被添加到核心蛋白前体上，随后迅速分泌到细胞外基质中。
