Wurzburg Beth A, Tarchevskaya Svetlana S, Jardetzky Theodore S
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA.
Structure. 2006 Jun;14(6):1049-58. doi: 10.1016/j.str.2006.03.017.
CD23, the low-affinity receptor for IgE (Fc epsilonRII), regulates IgE synthesis and also mediates IgE-dependent antigen transport and processing. CD23 is a unique Fc receptor belonging to the C-type lectin-like domain superfamily and binds IgE in an unusual, non-lectin-like manner, requiring calcium but not carbohydrate. We have solved the high-resolution crystal structures of the human CD23 lectin domain in the presence and absence of Ca2+. The crystal structures differ significantly from a previously determined NMR structure and show that calcium binding occurs at the principal binding site, but not at an auxiliary site that appears to be absent in human CD23. Conformational differences between the apo and Ca2+ bound structures suggest how IgE-Fc binding can be both calcium-dependent and carbohydrate-independent.
CD23，即IgE的低亲和力受体（FcεRII），可调节IgE的合成，还介导IgE依赖的抗原转运与加工。CD23是一种独特的Fc受体，属于C型凝集素样结构域超家族，以一种不同寻常的、非凝集素样的方式结合IgE，需要钙但不需要碳水化合物。我们已经解析了存在和不存在Ca2+时人CD23凝集素结构域的高分辨率晶体结构。这些晶体结构与先前确定的NMR结构有显著差异，表明钙结合发生在主要结合位点，而不是在人CD23中似乎不存在的辅助位点。无钙和结合Ca2+的结构之间的构象差异表明了IgE-Fc结合如何既能依赖钙又能不依赖碳水化合物。
