Superselective cell targeting through multivalent lectin-glycan interactions

所有的细胞都被一片由不同的碳水化合物组成的森林所覆盖，这种结构被称为糖萼。细胞表面的碳水化合物(多糖)有许多类型--有些是长的线形聚合物链，而另一些则是短的、高度分枝的结构，如小树。对于不同类型的细胞，糖萼的组成是不同的--虽然存在的多糖结构的范围可能是相似的，但每种糖的相对数量在不同类型的细胞之间可能有很大的不同。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，测量细胞上每种类型的多糖含量的唯一方法是将它们从细胞中切下来，并在质谱仪中单独称重。这个研究项目的目的是开发分子工具，可以用来定量一个完整的细胞表面存在多少特定的多糖，并以高选择性地结合到具有特定多糖组成的细胞。这些探针将在理解生物过程中有应用，并最终可能被用于医疗诊断和将药物定向输送到特定细胞类型。那么，如何区分具有相同细胞表面分子集的两个细胞，并且只在这些分子的相对丰度上存在差异？传统的探针，如抗体，通常只与目标分子的一个或两个拷贝高亲和力结合。它们可以用来判断细胞表面是否存在特定类型的分子，但不能用来选择性地结合目标分子的特定密度。密度依赖的“超选择性”结合需要一种不同的策略，这是受到糖生物学的启发--碳水化合物的生物学。糖类结合蛋白通常与其目标糖链相互作用相对较弱，而强相互作用是通过多个拷贝的糖链和糖链结合蛋白相互作用而实现的，即所谓的多价结合。通过这种方式，许多弱相互作用聚集在一起，提高了结合强度，但也大大提高了结合的选择性。在这里，我们将开发多价探针，它可以以密度依赖的方式与细胞表面的多糖结合。我们将开发能够区分癌细胞和健康细胞的探针，以及可以用来绘制调节神经细胞功能的复杂网状糖催化剂的探针。所开发的方法将在生物学和医学中具有高度特异性与靶细胞结合的更广泛的应用。

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.