Aubry J P, Pochon S, Gauchat J F, Nueda-Marin A, Holers V M, Graber P, Siegfried C, Bonnefoy J Y
Glaxo Institute for Molecular Biology, Geneva, Switzerland.
J Immunol. 1994 Jun 15;152(12):5806-13.
Human CD21 has been described as a receptor for the C3d,g and iC3b proteins of complement, for the Epstein-Barr virus, and also for IFN-alpha. We reported recently that CD23, a low affinity receptor for IgE (Fc epsilon R2), is a new functional ligand for CD21. To determine the site of interaction of CD23 on CD21, we analyzed the ability of purified recombinant CD23 incorporated into fluorescent liposomes to bind CD21 mutants bearing various deletions of extracytoplasmic short consensus repeats (SCRs). We found that the site of interaction of CD23 on CD21 is on SCRs 5 to 8, with contribution of SCRs 1 and 2. Tunicamycin treatment of CD21-transfected K562 cells strongly inhibited the binding of CD23-liposomes, suggesting that an N-linked sugar, present on SCRs 5 to 8, is involved in the CD23/CD21 interaction. By mutating together or individually, the three asparagines present on SCRs 5 to 8, asparagines (Asn) 370 and 295, but not Asn 492, were shown to be involved critically in the binding of CD23. Furthermore, we mapped the binding sites of a panel of anti-CD21 mAbs and found that at least six epitopes can be detected on CD21. The mAbs that inhibit the most CD23 binding to CD21 map in SCRs 5 to 8. This study indicates that SCRs 5 to 8 represent a novel functional domain on the CD21 molecule, and is the first demonstration of an activity of an extracytoplasmic region of the CD21 outside of SCRs 1 to 4.
人CD21已被描述为补体C3d、g和iC3b蛋白、爱泼斯坦-巴尔病毒以及干扰素α的受体。我们最近报道，IgE的低亲和力受体CD23（FcεR2）是CD21的一种新的功能性配体。为了确定CD23在CD21上的相互作用位点，我们分析了掺入荧光脂质体的纯化重组CD23与携带各种胞外短共有重复序列（SCR）缺失的CD21突变体结合的能力。我们发现CD23在CD21上的相互作用位点位于SCR 5至8，SCR 1和2也有贡献。用衣霉素处理转染了CD21的K562细胞强烈抑制了CD23脂质体的结合，这表明存在于SCR 5至8上的N-连接糖参与了CD23/CD21相互作用。通过共同或单独突变SCR 5至8上存在的三个天冬酰胺，发现天冬酰胺（Asn）370和295而非Asn 492在CD23结合中起关键作用。此外，我们绘制了一组抗CD21单克隆抗体的结合位点图谱，发现CD21上至少可检测到六个表位。抑制CD23与CD21结合最多的单克隆抗体定位在SCR 5至8。本研究表明，SCR 5至8代表CD21分子上一个新的功能结构域，并且首次证明了CD21胞外区域在SCR 1至4之外的活性。
