Interfacial metal and antibody recognition
Interfacial metal and antibody recognition
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DOI：
10.1073/pnas.0507267102
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发表时间：
2005-10-11
影响因子：
11.1
通讯作者：
Kwong, PD
中科院分区：
文献类型：
--
作者：
Zhou, TQ;Hamer, DH;Kwong, PD
金属离子的独特连接特性被蛋白质广泛利用，据估计，大约三分之一的蛋白质是金属蛋白。尽管抗体使用不同的识别机制，但据我们所知，从来没有一种抗体是使用界面金属的。我们之前描述了一个CD4反应性抗体家族，原型是Q425。CD4：Q425的结合不会干扰CD4：HIV-1 gp120包膜糖蛋白的结合，但它会阻止病毒进入所需的后续步骤。在这里，我们使用表面等离子体共振来表明Q425需要钙来识别CD4。具体地说，Q425与钙的结合导致对CD4的亲和力提高了55,000倍。X射线结晶学分析表明，Q425在钙、Ba2+或EDTA存在的情况下有一个暴露的金属结合部位，部分配位由来自四个抗体互补决定区的五个原子组成。结果表明，Q425对CD4的识别涉及到Q425持有的钙与抗原的直接连接，其中钙以大约1.5千卡/摩尔的结合能与CD4的每个连接原子结合。这一能量贡献，比典型的蛋白质原子更大，表明了界面金属连接如何在抗原识别中发挥独特的作用。
The unique ligation properties of metal ions are widely exploited by proteins, with approximately one-third of all proteins estimated to be metalloproteins. Although antibodies use various mechanisms for recognition, to our knowledge, none has ever been characterized that uses an interfacial metal. We previously described a family of CD4-reactive antibodies, the archetype being Q425. CD4:Q425 engagement does not interfere with CD4:HIV-1 gp120 envelope glycoprotein binding, but it blocks subsequent steps required for viral entry. Here, we use surface-plasmon resonance to show that Q425 requires calcium for recognition of CD4. Specifically, Q425 binding of calcium resulted in a 55,000-fold enhancement in affinity for CD4. X-ray crystallographic analyses of Q425 in the presence of Ca2+, Ba2+, or EDTA revealed an exposed metal-binding site, partially coordinated by five atoms contributed from four antibody complementarity-determining regions. The results suggest that Q425 recognition of CD4 involves direct ligation of antigen by the Q425-held calcium, with calcium binding each ligating atom of CD4 with approximate to 1.5 kcal/mol of binding energy. This energetic contribution, which is greater than that from a typical protein atom, demonstrates how interfacial metal ligation can play a unique role in antigen recognition.