Multivalent Sensing of Glycosaminoglycans on Vesicle Surfaces

糖胺聚糖（GAGs）是人体内最丰富的生物分子之一。例如，成年人体内大约有20克透明质酸，这是一种关键的结构GAG，在关节内起减震器的作用，在眼球内起填充物的作用。另一种重要的GAG是肝素，它是人体的抗凝血剂。肝素在医学上用于治疗深静脉血栓和心脏病发作（心肌梗死）。然而，随着分子生物学的最新进展，越来越明显的是，除了这些结构（透明质酸）和抗凝血（肝素）的作用外，它们在体内还有一系列其他重要功能，并可能参与疾病状态。肝素和透明质酸都与癌症的扩散（转移）有关，而肝素则与病毒感染有关。由此可见，体液中某些gag水平的变化可能是某些严重疾病的标志，例如，尿液中透明质酸水平增加100倍与膀胱癌的发生有关，而血液中透明质酸水平增加则表明肝功能衰竭。尽管GAGs在医学上具有重要意义，尤其是肝素和透明质酸，但很少有简单有效的方法来测量生物体液中GAGs的浓度。这些方法大多仅用于检测肝素，但即使这些方法也难以在临床环境中应用，或者容易受到其他生物分子的干扰。我们建议使用一种生物启发的方法来检测肝素和透明质酸，它复制了透明质酸与细胞表面相互作用的方式。我们将利用荧光的变化来测量肝素和透明质酸的浓度；荧光是一种非常灵敏的方法，可以检测到非常少量的待测分子。我们将利用我们在合成有机化学和物理有机化学方面的知识来开发传感器系统，以检测和区分不同类型的GAGs，以及不同长度的GAGs。这项研究不仅具有实际应用价值，提供了一种简单的方法来测量生物体液中与医学相关的gag水平，而且还可以研究具有多个结合位点的生物分子与细胞之间相互作用的基本原理。这些多价相互作用经常发生在细胞表面和细胞间传递信息的信号分子之间，但这种多价细胞表面结合过程的分子机制仍然知之甚少。

Glycosaminoglycans (GAGs) are one of the most abundant types of biomolecule within the human body. For example, in an adult human there is around 20g of hyaluronic acid, a key structural GAG that functions as a shock absorber within the joints and as a filler inside the eyeball. Another important GAG is heparin, which is the body's anticoagulant. Heparin is used medically in this capacity for the treatment of deep-vein thrombosis and heart attacks (myocardial infarction). However with recent advances in molecular biology it is becoming apparent that in addition to these structural (hyaluronic acid) and anticoagulant (heparin) roles, they have a range of other important functions in the body and can be involved in disease states. Both heparin and hyaluronic acid have been implicated in cancer spreading (metastasis), while heparin is involved in viral infection. It follows that changes in the levels of certain GAGs in bodily fluids can be markers for certain serious diseases, e.g. a 100-fold increase in the level of hyaluronic acid in the urine has been correlated with the occurrence of bladder cancer, whilst increased levels of hyaluronic acid in the blood are indicative of liver failure. Despite the medical importance of the GAGs, heparin and hyaluronic acid in particular, there are few simple and effective ways of measuring the concentrations of GAGs in biological fluids. Most of these methods have been developed to detect heparin only, but even these are either difficult to apply in a clinical environment or prone to interference by other biomolecules. We propose to use a bioinspired approach for the detection of heparin and hyaluronic acid, which copies the way that hyaluronic acid interacts with cell surfaces. We will use changes in fluorescence to measure the concentrations of heparin and hyaluronic acid; fluorescence is a very sensitive method that can detect very small amounts of the molecule to be measured. We will use our knowledge of synthetic organic chemistry and physical organic chemistry to develop sensor systems that will detect and discriminate between different types of GAGs, and GAGs of different lengths. Not only will this research have practical applications, giving a simple method of measuring the levels of medically-relevant GAGs in biological fluids, but will also allow investigation of the fundamental principles that govern interactions between biological molecules with multiple binding sites and cells. These multivalent interactions often occur between cell surfaces and the signalling molecules that deliver messages between cells, but the molecular mechanism of such multivalent cell surface binding processes is still poorly understood.