Elucidating the Molecular Basis of the Carbohydrate-Carbohydrate Interaction

Our goal in this project is to study, and in this way understand more fully, the ways in which a carbohydrate interacts with other carbohydrate units. While much is known of protein-protein and protein-carbohydrate interactions, we lack a detailed understanding of the corresponding carbohydrate-carbohydrate interactions (CCIs). These are, nevertheless, important in a wide range of biological contexts, e.g. fertilisation, cell-cell recognition and cell adhesion. A major issue associated with the study of CCIs is that they are inherently weak. For this reason, most work to date has been done within multivalent systems where many weak carbohydrate-based associations act cooperatively to provide an overall strong interaction (avidity). The best analogy for this is Velcro, where many little hooks with little individual strength, act together to provide immense combined sticking power. However, multivalent environments are necessarily macroscopic, and it is hard to probe the detail of the specific interactions involved; to retain the Velcro analogy, how do the hooks line up and which features of the hooks are important and which are not? For instance, we know that small changes in carbohydrate structure do lead to changes (either a gain or loss) of CCIs. However, the details how chemical/structural changes in the carbohydrate components translate to binding affinities is not understood. Our strategy to tackle this problem is new and is based on tethering (constraining) carbohydrate units on to a peptide scaffold which will encourage them to interact with one another. As our primary assay, we have designed sensitive systems that should respond to and, in turn, allow us to detect CCI's. We have other systems, which are more rigid, that will then allow us to localise carbohydrates and present them to one another, i.e. force them to interact. We will then use a range of spectroscopic methods to study the nature of any interaction with the aim of elucidating more of the molecular detail of the interactions involved. This will then lead to a better understanding of the mechanisms associated with CCIs, which are of fundamental importance in a range of biological environments. Insight into how these processes work (by understanding them at the molecular level), therefore, may then lead to approaches that could allow us to predict and engineer CCIs i.e. enhance or inhibit them, and turn them on or off. In turn, this understanding and the ability to identify and study new CCIs could be used to probe and thereby gain a better understanding of a given biology process. Thus, in essence, the long-term aim of this work is to contribute to our fundamental understanding of CCIs, which has implications for our knowledge of how nature uses this weak but important process, and to achieve this we propose a new approach to tackle the challenges that this field presents.