We have studied by electron microscopy a fascinating series of antidansyl monoclonal antibodies developed by Dangl et al. (Cytometry 2, 395-401, 1982) which have the same variable domain but different constant domains. Three of the four subclasses of mouse IgG were represented, IgG1, IgG2a and IgG2b. Previously, Oi et al. (Nature 307, 136-140, 1984) had examined the flexibilities of these antibodies by time-resolved fluorescence depolarization and found that IgG1 was least flexible, IgG2a was intermediate and IgG2b was the most flexible. In this communication we examine the conformations of circular complexes formed between these antibodies and a bivalent hapten, bis-dansyl cadaverine. The circular complexes were predominantly composed of two antibodies linked into a ring by two bivalent haptens, and are referred to as dimers, since only the antibody molecules are seen with the electron microscope. A few trimers and an occasional tetramer were also present in these preparations. For the least flexible IgG1, almost all (greater than 99%) of the circular dimers were "open-hinge" complexes with a hinge angle between the Fab arms of 100-120 degrees. For the intermediate IgG2a, most of the dimers were "open-hinge" complexes, but a larger percentage, 4 to 5%, had closed hinges with a hinge angle approaching 0 degrees. For the most flexible IgG2b, over 40% of the dimers were "closed-hinge" complexes. A model is proposed to explain these differences based upon orientation of the hapten in the combining site and differences in hinge structure.

译文

我们通过电子显微镜研究了由Dangl等人开发的一系列令人着迷的抗dansyl单克隆抗体 (Cytometry 2,395-401,1982),它们具有相同的可变结构域但具有不同的恒定结构域。代表了小鼠IgG的四个亚类中的三个,IgG1,IgG2a和IgG2b。以前,Oi等人 (Nature 307,136-140,1984) 通过时间分辨荧光去极化检查了这些抗体的柔韧性,发现IgG1是最不柔韧的,IgG2a是中间的,IgG2b是最柔韧的。在本交流中,我们检查了这些抗体与二价半抗原bis-dansyl尸胺之间形成的圆形复合物的构象。圆形复合物主要由两种通过两个二价半抗原连接成一个环的抗体组成,并且被称为二聚体,因为在电子显微镜下只能看到抗体分子。这些制剂中还存在一些三聚体和偶尔的四聚体。对于柔性最小的IgG1,几乎所有 (大于99%) 的圆形二聚体是 “开铰链” 复合物,其Fab臂之间的铰链角度为100-120度。对于中间体IgG2a,大多数二聚体是 “开铰链” 复合物,但较大的百分比 (4至5%) 具有铰链角度接近0度的闭合铰链。对于最灵活的IgG2b,超过40% 的二聚体是 “闭合铰链” 复合物。提出了一个模型来解释这些差异,该模型基于结合部位中半抗原的方向和铰链结构的差异。

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