ON THE STRUCTURE OF POLYMERIC IGM
ON THE STRUCTURE OF POLYMERIC IGM
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DOI：
10.1002/eji.1830180705
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发表时间：
1988-07-01
影响因子：
5.4
通讯作者：
SHULMAN, MJ
中科院分区：
文献类型：
--
作者：
DAVIS, AC;ROUX, KH;SHULMAN, MJ
免疫球蛋白μ的位置575处的半胱氨酸是重链被认为提供连接小鼠多聚IgM的单体亚基的唯一二硫键。该半胱氨酸在聚合IgM组装中的重要性通过使用定点诱变产生μ-半胱氨酸进行研究。在位置575处具有丝氨酸的链。30%的分泌的突变体IgM是共价组装的聚合物，这意味着Cys 575以外的半胱氨酸可以形成亚基间二硫键。根据蔗糖梯度沉降和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳迁移率判断，聚合的IgM缺乏J链，介导补体依赖性细胞溶解，并且似乎比传统的IgM五聚体具有更高的分子量。电子显微镜显示，突变IgM分子含有六个亚基。野生型IgM虽然主要以五聚体分子的形式合成，但以至少两种其他形式组装，其通过其电泳迁移率来区分。野生型IgM的明显更高分子量形式包括六聚体分子，其与六聚体突变体IgM一样，含有比五聚体形式少得多的J链，并且在激活补体依赖性细胞溶解方面效率高20倍。
The cysteine at position 575 of the immunoglobulin .mu. heavy chain is thought to provide the only disulfide bonds joining the monomer subunits of mouse polymeric IgM. The importance of this cysteine in the assembly of polymeric IgM was investigated by using site-directed mutagenesis to produce .mu. chains with serine at position 575. Thirty percent of the secreted mutant IgM was covalently assembled polymer implying that cysteines other than Cys575 can form inter-subunit disulfide bonds. The polymeric IgM lacked J chain, mediated complement-dependent cytolysis and appeared to have a higher molecular weight than conventional IgM pentamers, as judged by sucrose gradient sedimentation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobility. Electron microscopy revealed that the mutant IgM molecule contained six subunits. Wild-type IgM, while synthesized predominantly as a pentameric molecule, was assembled in at least two other forms, which were distinguished by their electrophoretic mobility. The apparently higher molecular weight forms of wild-type IgM include hexameric molecules which, like the hexameric mutant IgM, contained much less J chain that the pentameric form and were 20-fold more efficient at activating complement-dependent cytolysis.