Multivalent Sensing of Glycosaminoglycans on Vesicle Surfaces

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.