Revealing complexity of hyaluronan-protein interactions: novel tools and insights

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Hyaluronan (HA) is a large linear biopolymer made of simple sugar repeat units, a molecule highly conserved in vertebrates since their evolution 500 million years ago. Present in the extracellular matrix of all mammalian tissues, HA exhibits an astonishing array of biological functions. HA dictates tissue architecture, elasticity, hydration and permeability, and also directs cell behaviour via engagement with cell surface receptors, such as CD44 and LYVE-1. HA is implicated in a wide range of physiological and pathological processes, including development, inflammation and tissue repair, immune response, tumour development and virus/bacteria infections.HA contributes widely to a diversity of biological functions through its interaction with a repertoire of HA-binding proteins. On its own, HA does not adopt defined structures but remains intrinsically disordered. It differentially organises, adopts and assumes various conformations and modes of interactions upon binding to different HA-binding proteins, somewhat similar to water conforming to the shape of its container. The level of complexity in how HA interacts with proteins is high. An analogy can be made to nucleic acids; however, compared to DNA and RNA, our understanding of the molecular and physical mechanisms underpinning HA functions under the influence of proteins is still in its infancy. The reasons for this are primarily technical: we lack the biophysical tools to probe the complexity of molecular interactions involving HA, and the ability to make defined 'designer' HA molecules.This project will directly address these technical bottlenecks. It aims to generate a new toolkit required to reveal the biophysical phenomena underpinning the complex interactions of HA and HA binding proteins. Specific questions that we address with the toolkit are:How do the HA cell surface receptors recognise the topology of HA chains (e.g., by selectively binding to free chain ends), and how can proteins slide along HA chains (similar to polymerase sliding along DNA)? Answers to these questions will help defining the molecular mechanisms by which HA-receptor interactions critically support immune cell trafficking.How do extracellular matrix proteoglycans assemble with an HA chain into a super-helix, and what are the mechanical characteristics of such HA/protein 'supramolecular springs'? This is relevant for the elasticity of soft and dynamic HA-rich extracellular matrices that are formed during tissue development and repair, but also during early stages of tumour development and other diseases, to promote the migration of cells.HA-protein interactions control how cells recognise each other, shape tissues, and migrate for immune surveillance and tissue repair. They are also opportunistically exploited by cancer cells for metastasis in distant organs, and by pathogenic bacteria/viruses to infect tissues/cells. Revealing the complexity, but not only the mere presence of absence, of HA and its interactions with proteins, will ultimately open up new avenues to better control such processes (e.g., to block the priming of damaging immune responses following tissue transplantation), and to design biomaterials with novel functions for applications in regenerative medicine and immune regulation. The project will also lead the way, by providing new reagents and protocols, for other biophysicists to study HA-protein interactions, and glycosaminoglycan-protein interactions more generally, with biophysical methods to reveal the molecular mechanisms underpinning their many functions.