Structural Studies of Protein-Carbohydrate Interactions

抗体对外来分子(称为抗原)的识别是免疫的一个关键方面，但令人惊讶的是，人们对结合的分子机制知之甚少。有趣的是，免疫系统以不同的方式处理不同类型的分子。例如，当携带抗体的细胞(称为B细胞)遇到蛋白质抗原时，它可以将其切成碎片呈现给T细胞。如果T细胞也识别这种蛋白质是外来的，它可以刺激B细胞产生大量高度特异的紧密结合抗体。然而，当B细胞与碳水化合物结合时，T细胞几乎不会起到这种作用。 这项研究的重点是试图在分子水平上了解抗体是如何结合碳水化合物的。我们的目标是(1)确定免疫系统是否进化到能够快速识别碳水化合物抗原，以弥补T细胞“帮助”的不足。(2)阐明“交叉反应”的基础，即抗体与化学上相似的抗原(在我们的案例中是碳水化合物)结合。(3)我们知道存在针对碳水化合物的抗体，这些抗体还可以结合‘模仿’碳水化合物的蛋白质或DNA，因此我们的目标是确定这种‘多重特异性’的分子机制。(4)获得通过改变形状可以针对完全不同的抗原的单一抗体的分子证据。 我们与世界各地的科学团体合作，这些团体生产了针对各种重要碳水化合物抗原(通常来自细菌)的抗体，并仔细测量了结合强度并确定了所有抗体的特异性。我们的研究方法是自己产生高质量的抗体晶体，并与碳水化合物结合。然后，我们使用一种名为x射线结晶学的技术，通过测量晶体如何衍射x射线来成像分子结构，这样我们就可以准确地看到抗体是如何结合它们的抗原的。这项研究已经扩展了关于抗体结合的已知内容，并有望为一些结合理论提供戏剧性的证据。

The recognition by antibodies of foreign molecules (called antigens) is a key aspect of immunity, but surprisingly little is known about the molecular mechanisms of binding. Interestingly, the immune system treats different kinds of molecules in different ways. For example, when an antibody-bearing cell (called a B-cell) encounters a protein antigen it can chop it into bits to present to T-cells. If a T-cell also recognizes the protein as foreign, it can stimulate B-cells into producing vast quantities of highly-specific tightly-binding antibodies. However, T-cells almost never help this way when a B-cell binds a carbohydrate. This research is focussed on trying to understand at a molecular level how antibodies bind carbohydrates. We have the objectives (1) To determine if the immune system evolved to recognize carbohydrate antigens quickly to make up for the lack of T-cell 'help.' (2) To elucidate the basis for 'cross-reactivity,' where an antibody binds to antigens (in our case carbohydrates) that are chemically similar. (3) We know that there are antibodies specific for carbohydrates that also bind proteins or DNA that 'mimic' carbohydrates, so we aim to determine the molecular mechanism for this 'polyspecificity.' (4) To obtain molecular evidence that by shifting their shapes a single antibody can be specific for completely different antigens. We work in collaboration with scientific groups around the world who have produced antibodies to various important carbohydrate antigens (usually from bacteria) and who have carefully measured the strength of binding and determined the specificities of all of their antibodies. Our investigative method is to generate high-quality crystals of the antibodies by themselves and bound to the carbohydrates. We then use a technique called 'x-ray crystallography' to image the structures of the molecules by measuring how the crystals diffract x-rays, so we can actually see exactly how the antibodies bind their antigens. This research has already expanded what is known about antibody binding, and has the promise of providing dramatic proof of some theories of binding.