The structural analysis of shark IgNAR antibodies reveals evolutionary principles of immunoglobulins
The structural analysis of shark IgNAR antibodies reveals evolutionary principles of immunoglobulins
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DOI：
10.1073/pnas.1321502111
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发表时间：
2014-06-03
影响因子：
11.1
通讯作者：
Buchner, Johannes
中科院分区：
文献类型：
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作者：
Feige, Matthias J.;Graewert, Melissa A.;Buchner, Johannes
鲨鱼和其他软骨鱼是进化上最古老的生物，它们依赖抗体作为其适应性免疫系统的一部分。它们产生免疫球蛋白新抗原受体(IgNAR)，这是一种只有同源二聚体的重链抗体，作为它们体液适应性免疫反应的主要部分。在这里，我们报告了IgNAR恒定域的原子分辨结构和这种重链抗体的结构模型。我们发现，尽管序列保守性很低，但现代抗体的基本Ig折叠已经存在于进化的古代鲨鱼IgNAR结构域中，突出了无处不在的Ig折叠的关键结构决定因素。相比之下，人和鲨鱼抗体结构域之间的差异解释了几个IgNAR结构域的高度稳定性，并使我们能够设计人抗体以提高稳定性和分泌效率。我们确定了两个恒定结构域，C1和C3，它们在IgNAR中充当二聚化模块。结合单个的结构域结构和小角X射线散射，这使得我们能够开发出完整的IgNAR分子的结构模型。它的恒定区域呈现出伸长的形状，具有灵活性，中间有一个特有的扭结。尽管缺乏典型的铰链区，但可变区的间隔适当宽，可以与多种抗原结合。因此，鲨鱼的IgNAR结构域已经显示出众所周知的Ig折叠，但除此之外，这种只有重链的抗体使用独特的方式进行二聚化和功能模块的定位。
Sharks and other cartilaginous fish are the phylogenetically oldest living organisms that rely on antibodies as part of their adaptive immune system. They produce the immunoglobulin new antigen receptor (IgNAR), a homodimeric heavy chain-only antibody, as a major part of their humoral adaptive immune response. Here, we report the atomic resolution structure of the IgNAR constant domains and a structural model of this heavy chain-only antibody. We find that despite low sequence conservation, the basic Ig fold of modern antibodies is already present in the evolutionary ancient shark IgNAR domains, highlighting key structural determinants of the ubiquitous Ig fold. In contrast, structural differences between human and shark antibody domains explain the high stability of several IgNAR domains and allowed us to engineer human antibodies for increased stability and secretion efficiency. We identified two constant domains, C1 and C3, that act as dimerization modules within IgNAR. Together with the individual domain structures and small-angle X-ray scattering, this allowed us to develop a structural model of the complete IgNAR molecule. Its constant region exhibits an elongated shape with flexibility and a characteristic kink in the middle. Despite the lack of a canonical hinge region, the variable domains are spaced appropriately wide for binding to multiple antigens. Thus, the shark IgNAR domains already display the well-known Ig fold, but apart from that, this heavy chain-only antibody employs unique ways for dimerization and positioning of functional modules.