Lowell C A, Klickstein L B, Carter R H, Mitchell J A, Fearon D T, Ahearn J M
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
J Exp Med. 1989 Dec 1;170(6):1931-46. doi: 10.1084/jem.170.6.1931.
Complement receptor type 2 (CR2;CD21), a member of the superfamily of proteins containing short consensus repeats (SCRs), is the B cell receptor for both the gp350/220 envelope protein of Epstein-Barr virus (EBV), and for the C3dg protein of complement. By analysis of CR2 deletion mutants and chimeras formed with CR1 (CD35) we determined that of the 15 SCRs in CR2, the NH2-terminal two SCRs are necessary and sufficient to bind both gp350/220 and C3dg with affinities equivalent to those of the wild-type receptor. The epitope for OKB-7, a mAb that blocks binding of both EBV and C3dg and shares with these ligands B cell-activating capabilities, also requires both SCR-1 and SCR-2, whereas mAbs lacking these functions bind to other SCRs. Thus, EBV, a polyclonal activator of B cells, has selected a site that is proximate or identical to the natural ligand binding site in CR2, perhaps reflecting the relative immutability of that site as well as its signal transducing function.
补体受体2（CR2；CD21）是含有短共有重复序列（SCR）的蛋白质超家族成员，它是爱泼斯坦-巴尔病毒（EBV）的gp350/220包膜蛋白以及补体C3dg蛋白的B细胞受体。通过对CR2缺失突变体和与CR1（CD35）形成的嵌合体进行分析，我们确定CR2中的15个SCR中，氨基末端的两个SCR对于结合gp350/220和C3dg是必需且足够的，其亲和力与野生型受体相当。OKB-7是一种单克隆抗体，可阻断EBV和C3dg的结合，并与这些配体共享B细胞激活能力，其表位也需要SCR-1和SCR-2，而缺乏这些功能的单克隆抗体则与其他SCR结合。因此，EBV作为B细胞的多克隆激活剂，选择了一个与CR2中天然配体结合位点相近或相同的位点，这可能反映了该位点的相对不变性及其信号转导功能。
