Schweitzer-Stenner R, Ortega E, Pecht I
Institute of Experimental Physics, University of Bremen, Germany.
Biochemistry. 1994 Jul 26;33(29):8813-25. doi: 10.1021/bi00195a025.
Clustering of the type I receptor for Fc epsilon domains constitutes the signal initiation leading to mast cell secretory response. In order to characterize the relationship between the lifetime of clustered Fc epsilon receptors and the cellular response we have studied the rates of association and dissociation of monoclonal, IgG class antibodies (mAbs) specific for the alpha-subunit of type 1 receptor for IgE (Fc epsilon RI) (designated as F4, J17, and H10) to and from this receptor on live rat mucosa-type mast cells (line RBL-2H3) were measured at three different temperatures (25, 15, and 4 degrees C). These antibodies dimerize the Fc epsilon RI on these cells and induce their secretion, thus providing clear evidence that Fc epsilon receptor dimers are sufficient for the stimulus [Ortega et al. (1988), EMBO J. 7, 4101]. Marked differences in the response to the different mAbs have been explained in terms of possible orientational constraints imposed by them on the Fc epsilon receptor dimers. Interaction kinetics between the Fab fragments of these mAbs and the Fc epsilon RI have previously been measured and found to be best fitted by a two-reaction-step model involving a conformational transition from a low-affinity (l) to a high-affinity (h) state of the receptor-ligand complex [Ortega et al. (1991) Biochemistry 30, 3473]. Analysis of the interaction kinetics between the corresponding intact mAbs and the Fc epsilon RI therefore requires consideration of this 1-->h transition for both complexes involved, namely, the monomeric Fc epsilon RI-mAb and the dimeric Fc epsilon RI-mAb-Fc epsilon RI complexes. This was done by assuming the involvement of the following Fc epsilon RI dimer species: all 1- or h-state dimers Dll and Dhh and a hybrid Dlh with one receptor in the l state and the other in the h state. A self-consistent set of rate constants was derived by fitting the experimental results to this model. At 25 degrees C the all-h-state dimers Dhh turned out to be preferentially stabilized, probably by interaction with other cellular components. Different dimer formation rates were observed for each of the three mAbs, indicating that the dimer distribution among different states is determined by the individual epitope-binding site combination and also by the geometry of the respective complexes.(ABSTRACT TRUNCATED AT 400 WORDS)
Fcε结构域I型受体的聚集构成了导致肥大细胞分泌反应的信号起始过程。为了表征聚集的Fcε受体的寿命与细胞反应之间的关系，我们研究了针对IgE 1型受体（FcεRI）α亚基的单克隆IgG类抗体（mAb）（分别命名为F4、J17和H10）与活大鼠黏膜型肥大细胞（RBL-2H3细胞系）上该受体的结合和解离速率，测量是在三个不同温度（25、15和4℃）下进行的。这些抗体使这些细胞上的FcεRI二聚化并诱导其分泌，从而提供了明确证据，表明Fcε受体二聚体足以产生刺激作用[奥尔特加等人（1988年），《欧洲分子生物学组织杂志》7卷，4101页]。对不同mAb反应的显著差异已根据它们对Fcε受体二聚体可能施加的取向限制进行了解释。此前已测量了这些mAb的Fab片段与FcεRI之间的相互作用动力学，发现其最适合由一个双反应步骤模型来描述，该模型涉及受体 - 配体复合物从低亲和力（l）状态到高亲和力（h）状态的构象转变[奥尔特加等人（1991年），《生物化学》30卷，3473页]。因此，分析相应完整mAb与FcεRI之间的相互作用动力学需要考虑所涉及的两种复合物（即单体FcεRI - mAb和二聚体FcεRI - mAb - FcεRI复合物）的这种l→h转变。这是通过假设涉及以下FcεRI二聚体种类来完成的：所有l态或h态二聚体Dll和Dhh，以及一种一个受体处于l态而另一个处于h态的杂合二聚体Dlh。通过将实验结果拟合到该模型得出了一组自洽的速率常数。在25℃时，全h态二聚体Dhh被证明优先稳定，可能是通过与其他细胞成分相互作用实现的。观察到三种mAb各自的二聚体形成速率不同，这表明不同状态之间的二聚体分布由单个表位结合位点组合以及各自复合物的几何形状决定。（摘要截取自400字）
