Bartlett W C, Kelly A E, Johnson C M, Conrad D H
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond 23298, USA.
J Immunol. 1995 May 1;154(9):4240-6.
The low-affinity receptor for IgE (Fc epsilon RII/CD23) is a type II integral membrane protein with an extracellular C-terminal sequence homologous to C-type animal lectins. Between this region and the membrane is a repetitive sequence predicted to form an alpha-helical coiled-coil and is termed the stalk region. The Fc epsilon RII is proteolytically cleaved when at the cell surface in this stalk region. Both the 38 Kd and 28 Kd major released fragments were isolated from culture media and N-terminal sequencing demonstrated that the cleavage sites were in the third and fourth repeat domains, respectively. The identified sites show no apparent similarity with the cleavage sites previously identified in human Fc epsilon RII. Recent studies have demonstrated that the intact Fc epsilon RII interacts with IgE with a dual-affinity, resulting from a multivalent interaction with the IgE Fc region; mutant Fc epsilon RII that have a disruption of the alpha-helical coiled-coil have a single low-affinity interaction consistent with a monomeric interaction with IgE. The soluble Fc epsilon RII were shown to interact with IgE with an affinity similar to these mutant Fc epsilon RII. Preparation of a chimeric Fc epsilon RII in which the transmembrane and cytoplasmic regions were replaced with sequences from Ly-49 revealed that these regions played no role in the multimeric association of the Fc epsilon RII necessary for dual-affinity interaction with IgE. In addition, a full-sized soluble Fc epsilon RII construct was expressed, and this molecule demonstrated increased capacity to interact with IgE.
IgE的低亲和力受体（FcεRII/CD23）是一种II型整合膜蛋白，其细胞外C末端序列与C型动物凝集素同源。在该区域和膜之间是一个预测形成α-螺旋卷曲螺旋的重复序列，称为柄区。当FcεRII在细胞表面的这个柄区时会被蛋白水解切割。从培养基中分离出38 Kd和28 Kd的主要释放片段，N端测序表明切割位点分别在第三个和第四个重复结构域。所确定的位点与先前在人FcεRII中确定的切割位点没有明显相似性。最近的研究表明，完整的FcεRII与IgE以双亲和力相互作用，这是由于与IgE Fc区的多价相互作用导致的；破坏了α-螺旋卷曲螺旋的突变型FcεRII具有单一的低亲和力相互作用，这与与IgE的单体相互作用一致。可溶性FcεRII与IgE相互作用的亲和力与这些突变型FcεRII相似。制备一种嵌合FcεRII，其中跨膜和细胞质区域被Ly-49的序列取代，结果表明这些区域在FcεRII与IgE双亲和力相互作用所需的多聚体缔合中不起作用。此外，表达了一种全长可溶性FcεRII构建体，该分子与IgE相互作用的能力增强。
