Multivalent Sensing of Glycosaminoglycans on Vesicle Surfaces

Lead Research Organisation: University of Manchester
Department Name: Chemistry

Abstract

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.

Publications

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Brown JR (2014) Fructose controlled ionophoric activity of a cholate-boronic acid. in Organic & biomolecular chemistry

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Devi U (2011) Pd(II)-mediated assembly of porphyrin channels in bilayer membranes. in Langmuir : the ACS journal of surfaces and colloids

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Webb SJ (2013) Supramolecular approaches to combining membrane transport with adhesion. in Accounts of chemical research

 
Description Our aim of this PhD studentship was to improve understanding of the molecular recognition of polysaccharides at membranes, in particular developing synthetic lipids that will recognize and report on the presence of glycosaminoglycan (GAG) saccharides, like hyaluronic acid (HA); elevated levels of HA are implicated in bladder carcinoma and osteoarthritis. As well as sensing applications, we used these lipids to throw light on one of the more poorly understood aspects of fundamental research in physical organic chemistry.

We started by synthesizing a boronic acid capped lipid with a fluorinated fluorescent reporter group that we knew could give a fluorescent signal due to analyte-induced fluorescence quenching and changes in the lateral distribution of the reporter groups. These boronic acid capped fluorinated lipids gave a fluorescent signal upon interaction with simple mono- and poly- saccharides, albeit with unexpectedly weak binding (given observations by other researchers in methanol). These studies also revealed several complicating factors, including local pH changes and surface charge on the oligosaccharides.

We then sought to quantify the weaker binding of saccharides to membrane bound boronic acids. A series of novel fluorescent and chromogenic lipids with reporter groups close to the boronic acids were synthesized and studied. Complementary competition binding assays with the dyes Alizarin Red S and Pyrocatechol Violet were also completed. These studies allowed the effect of the membrane on saccharide/boronic acid recognition to be quantified for the first time; we showed the lower polarity of the membrane interface weakened the interaction 32-fold. Furthermore we were able to quantify the effect of multivalency in solution (2-fold increase per binding group). We have proposed a model for the saccharide/boronic acids interaction in membranes that explains many of these unexpected observations, this work is being prepared for publication.

We also devised a parallel approach to that outlined in the original proposal that used saccharides to open or close synthetic membrane channels; release of an ion or dye and generates a fluorescent signal that amplifies the original recognition event and improve sensitivity. Proof-of-principle studies using palladium ions to open dye-transporting channels were successful and published in 2011. These studies were followed by the synthesis of boronic acid-capped lipids and studies of alkali metal ion release in the presence or absence of saccharides. These compounds successfully gave a response to fructose (decreasing the fluorescence of an enclosed dye) but gave no response to other saccharides, including HAs. The studies described above allowed us to develop a testable model that explained the behavior of these ion-transporting lipids (ionophores). This work is the first example of a boronic acid ionophore that is switchable by a saccharide, and is being prepared for publication.
Exploitation Route We have developed a model for saccharide/boronic acid interactions that is a valuable addition to the physical organic chemistry of membranes. We have also developed an ionophoric sensor for a simple monosaccharide. Initial studies were reported at the 2009 Manchester Biomolecular Symposium and two international meetings; the 42nd IUPAC Congress (Glasgow) in 2009 (P704_033, also selected for a flash presentation) and the 3rd EuCheMS Chemistry Congress (Nuremberg) in 2010 (part funded by award of a RSC Bursary). Some of the research was published in 2011 (Devi U; Brown JRD; Almond A; Webb SJ, Langmuir 2011, 27, 1448) in an invited submission for a "Supramolecular Chemistry at Interfaces" special issue. A later publication appeared in Org. Biomol. Chem. 2014, 12, 2576-2583, which was selected by the editors as a "hot" article in March 2014.
Sectors Healthcare

Pharmaceuticals and Medical Biotechnology

URL http://www.webblab.org
 
Description Although a selective sensor for GAGs was not developed, this collaboration between Drs Almond and Webb has also lead to consultancy work with Rolls-Royce (IP protection ongoing).
First Year Of Impact 2009
Sector Agriculture, Food and Drink
Impact Types Economic

 
Description Rolls-Royce 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
PI Contribution The collaboration between Drs Almond and Webb has also lead to consultancy work with Rolls-Royce.
Collaborator Contribution Advice and consultancy
Impact IP protection explored
Start Year 2009
 
Description University of Manchester Open Day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Talked to indivual visitors about the useful of chemistry to society, exemplified by examples from our research

None
Year(s) Of Engagement Activity 2007,2009,2011