Sidman C, Potash M J, Köhler G
J Biol Chem. 1981 Dec 25;256(24):13180-7.
The role of specific structural elements in glycoprotein metabolism and secretion was studied using the IgM mu chains from normal and mutant hybridoma cell lines. Five classes of altered mu chains were studied, all of which lacked various portions of the normal protein sequence, and three of which had one and the others two fewer carbohydrate units than wild type mu. One mutant secreted mu chains more rapidly than wild type cells. Two of the mutant cell lines secreted very little IgM, and both of these degraded intracellular mu chains at an abnormally high rate. Tunicamycin largely blocked IgM secretion in wild type and three mutant cell lines, but caused less inhibition in the two other mutant lines. When glycosylation in the two low secreting mutants was blocked by tunicamycin, degradation of mu chains was substantially reduced in one but unaffected in the other. All of the above properties were retained by the altered mu chains when the mutants were further hybridized with cells producing wild type mu. Overall, the various carbohydrate units and polypeptide sequences seem to play different roles in a single protein's metabolism and expression. The carbohydrate moieties may exert independent effects on protein degradation and on secretion.
利用来自正常和突变杂交瘤细胞系的IgM μ链，研究了特定结构元件在糖蛋白代谢和分泌中的作用。研究了五类改变的μ链，所有这些μ链都缺少正常蛋白质序列的不同部分，其中三类比野生型μ链少一个碳水化合物单元，另外两类少两个碳水化合物单元。一种突变体分泌μ链的速度比野生型细胞快。两个突变细胞系分泌的IgM很少，并且这两个细胞系都以异常高的速率降解细胞内的μ链。衣霉素在很大程度上阻断了野生型和三个突变细胞系中的IgM分泌，但在另外两个突变系中引起的抑制作用较小。当衣霉素阻断两个低分泌突变体中的糖基化时，一个突变体中μ链的降解显著减少，而另一个突变体中则不受影响。当突变体与产生野生型μ链的细胞进一步杂交时，改变的μ链保留了上述所有特性。总体而言，各种碳水化合物单元和多肽序列似乎在单一蛋白质的代谢和表达中发挥不同的作用。碳水化合物部分可能对蛋白质降解和分泌产生独立的影响。
