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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - GlycoPeptides (Exploiting in vitro evolution of macrocyclic glycopeptides to explore selectin interactions)

Teaser

Summary

Immune cells use complex sugars called glycans to recognise other cells and find their correct site of activity. When this goes wrong, this can lead to under- or over-activation of the immune system and results in disease states like auto-immunity or poor clearance of cancer cells. One of the molecules that immune cells use for recognising glycans is the family of proteins called selectins. The three proteins in this family are present on different types of cells, such as the cells that make up blood vessels, and \'grab hold\' of the immune cells when there is a problem, such as inflammation. This causes the immune cell to slow down in blood circulation, and escape into the surrounding tissue where they are needed. This interaction, between selectins on the surface of blood vessels and the glycans on immune cells, is therefore very important for targeting the immune system to its site of action.

The interaction between proteins and sugars is often weak, requiring many interactions to work together to give a strong effect. For this reason, it has been difficult to find molecules that can be used to target selectins. In this work, we investigated the interaction between selectins and glycans and tried to find molecules that can be used to disrupt the selectin-glycan interaction. These might eventually be useful in medicine, for example preventing chronic inflammation or stopping cancer cells from hijacking this adhesion process to spread throughout the body.

Our objectives were to find molecules that could bind strongly and selectively to each of the three selectins. To achieve this, we modified a system for generating tens of billions of different compounds at a time, with DNA used as a barcode to allow identification of which of these many different molecules can bind to the selectin. This required us to develop some new chemical tools to allow this pool of molecules to better resemble the glycans that selectins normally bind to, improving our chances of success. We also aimed to use this vast pool of different molecules to look for patterns of binding that might teach us more about how selectins work.

Work performed

We developed an approach that allowed one of the key interactions between selectins and the glycans they bind to be stably mimicked. Because the molecules we made were based on peptides, made of the same building blocks as proteins, they can be generated using the same molecular machinery that cells use in making proteins. This allows us to make a vast number of molecules very easily, but it limits the building blocks that can be used. To overcome this, we employed a technology called genetic code reprogramming, where these natural building blocks can be replaced with synthetic ones of our choosing. In this case, we thus made a synthetic building block that looks like one of the crucial interacting parts of the glycans that bind to selectins. The first part of this project was focussed on developing the chemical tools necessary for making this collection of molecules.

With these tools ready, we looked for specific molecules from this pool of tens of billions of different options that could bind specifically to E-selectin (one of the three types of selectin). This proved successful, and we identified several promising candidate molecules that we are now in the process of testing. These results will lead to a publication in an academic journal, and potentially developed further as treatment for diseases where selectin involvement has been shown.

Final results

This project involved development of new chemical tools for producing vast collections of peptide-based molecules. Using these tools we discovered promising candidate molecules that may allow us to prevent immune cell recruitment by selectins. This offers the possibility of finding much more selective, and therefore safer, molecules that can disrupt protein-sugar interactions. Because protein-sugar interactions are at the core of a lot of cellular recognition processes, our results potentially open up new avenues for development of drugs.