Superselective cell targeting through multivalent lectin-glycan interactions

所有的细胞都被一个由各种各样的碳水化合物组成的森林所覆盖，这个森林被称为糖萼。有许多类型的细胞表面碳水化合物（聚糖）-一些是长的线性聚合物链，而另一些则具有短的高度分支的结构，如小树。对于不同类型的细胞，糖萼的组成是不同的-虽然存在的聚糖结构的范围可以是相似的，但每种聚糖的相对量可以从一种类型的细胞到另一种类型的细胞有很大的变化。如果细胞发生癌变，糖萼的组成也会发生变化，因此测量糖萼的组成为癌症诊断提供了机会。目前，测量细胞上每种聚糖的数量的唯一方法是将它们从细胞上切下来，然后在质谱仪中单独称重。该研究项目的目的是开发分子工具，可用于量化完整细胞表面上存在多少特定聚糖，并以高选择性结合具有特定聚糖组成的细胞。这些探针将应用于了解生物过程，并最终可用于医学诊断和针对特定细胞类型的药物递送。那么，如何区分具有相同细胞表面分子组的两个细胞，而这些分子的相对丰度不同？传统的探针如抗体通常仅以高亲和力结合其靶分子的一个或两个拷贝。它们可以用来判断细胞表面是否存在特定类型的分子，但不能选择性地结合特定密度的靶分子。密度依赖性的“超选择性”结合需要一种不同的策略，这种策略的灵感来自于糖生物学-碳水化合物的生物学。碳水化合物结合蛋白通常与其靶聚糖的相互作用相对较弱，而强相互作用是通过使多个聚糖拷贝和聚糖结合蛋白彼此协同相互作用（所谓的多价结合）来实现的。这样，许多弱相互作用聚集在一起，增强了结合强度，但也大大增强了结合的选择性。在这里，我们将开发多价探针，可以结合在一个密度依赖性的方式细胞表面聚糖。我们将开发能够区分癌细胞和健康细胞的探针，以及可用于绘制复杂的网状糖萼的探针，这些糖萼调节神经元细胞的功能。所开发的方法将在生物学和医学中具有更广泛的应用，以高度特异性地结合靶细胞。

All cells are covered in a forest of diverse carbohydrates structures known as the glycocalyx. There are many types of cell-surface carbohydrates (glycans) - some are long linear polymer chains, while others have short highly branched architectures like small trees. The composition of the glycocalyx is different for different types of cells - while the range of glycan structures present can be similar, the relative quantities of each glycan can vary considerably from one type of cell to another. Glycocalyx composition also changes if a cell becomes cancerous, and so measuring the composition of a glycocalyx presents opportunities for cancer diagnosis. Currently, the only way to measure how much of each type of glycan is present on a cell is to chop them off the cell, and weigh them individually in a mass spectrometer. The aim of this research project is to develop molecular tools that can be used to quantify how much of a particular glycan is present on an intact cell surface, and to bind with high selectivity to cells that have a particular glycan composition. These probes will have applications in understanding biological processes, and could ultimately be used as medical diagnostics and for targeted delivery of drugs to specific cell types.So how do you differentiate between two cells that have the same set of cell surface molecules, and differ only in the relative abundance of those molecules? Traditional probes like antibodies usually bind with high affinity to only one or two copies of their target molecule. They can be used to tell if a specific type of molecule is present on a cell surface, but not to bind selectively in response to a specific density of their target molecules. Density-dependent 'superselective' binding requires a different strategy that is inspired by glycobiology - the biology of carbohydrates. Carbohydrate-binding proteins often interact relatively weakly with their target glycan and strong interactions are achieved by having many copies of the glycans and glycan-binding proteins interacting with one another in concert - so-called multivalent binding. In this way, many weak interactions come together to enhance binding strength, but it also greatly enhances the selectivity of binding. Here we will develop multivalent probes that can bind in a density-dependent manner to cell surface glycans. We will develop probes that can distinguish between cancerous and healthy cells, and probes that can be used to map out complex net-like glycocalyces that regulate the function of neuronal cells. The methods developed will have much broader application for highly specific binding to target cells in both biology and medicine.