AbstractsBiology & Animal Science

Glycosaminoglycans (GAGs) are linear polysaccharides, built of periodically occurring disaccharide units. GAGs are ubiquitous in the extracellular matrix (ECM), where they exhibit multifarious biological activities. This diversity arises from - among others - their ability to interact with and regulate a large number of proteins, such as cytokines, chemokines, and growth factors. As of the huge variety in their chemical configuration, GAGs are further sub-classified into different types (heparin, for instance, is one of these sub-classes). Hence, GAGs are a diverse class of molecules, which surely contributes to the broadness of their spectrum of biological functions. Through varying arrangements of sulfate groups and different types of saccharide units, individual GAG molecules can establish specific atomic contacts to proteins. One of the best-studied examples is antithrombin-heparin, whose biologically relevant interaction requires a specific pentasaccharide sequence. It is valid to assume, however, that various proteins are yet to be discovered whose biological functions are in some way affected by GAGs. In other cases, and this is true for the cytokine interleukin-10 (IL-10), there are already experimental indications for a biologically relevant protein-GAG interaction, but the details are still obscure and the fundamental molecular interaction mechanism has still not been clarified. IL-10 has been shown to bind GAGs. So far, however, no structural detail about IL-10-GAG interaction is known. Function-wise, IL-10 is mainly considered to be immunosuppressive and therefore anti-inflammatory, but it in fact has the pleiotropic ability to influence the immune system in both directions, i.e. it constitutes a complex regulation system on its own. Therefore, the role of GAGs in this system is potentially substantial, but is yet to be clarified. In vitro experiments have yielded indications for GAGs being able to modulate IL-10\'s biological function, and obviously IL-10 and GAGs are simultaneously present in the ECM. This gives rise to the assumption that IL-10-GAG interaction is of biological significance, and that understanding the impact of GAGs on IL-10 biology is important - from the basic research point of view, but also for the development of therapies, potentially involving artificially designed ECMs. A promising approach for obtaining knowledge about the nature of IL-10-GAG interaction is its investigation on the structural level, i.e. the identification and characterization of the molecular interaction mechanisms that govern the IL-10-GAG system. In this PhD project it was my goal to reveal structural and molecular details about IL-10-GAG interaction with theoretical and computational means, and with the help of experiments performed by collaborators in the framework of the Collaborative Research Centre DFG Transregio 67. For achieving this, I developed three methods for the in silico investigation of protein-GAG systems in general and subsequently applied them to the IL-10-GAG system. Parts of that work…