Controlling and Understanding IgE Glycosylation

Antibodies (Abs) are critical components of the human immune system. They circulate as so called glycoproteins in the serum, referring to an important protein modification, namely the attachment of sugar residues (glycans) to the protein backbone. There has been mounting evidence favouring the role of glycans in the modulation of Ab activities. However a broader understanding is lacking mainly due to the complex structure of glycans. Here we aim to investigate Immunoglobulin E (IgE) glycosylation. This antibody class, mainly involved in allergy and parasite infections, is particularly complex glycosylated, over 40 structures are usually present on serum IgE. We aim to investigate the impact of glycosylation to the structure and function of IgE antibodies. The proposal focuses on the production of IgE with precisely defined glycosylation profiles using a unique plant based expression platform, enabling large flexibility in glycan engineering. This requires a detailed understanding how glycans are processed and synthesized on IgE molecules. Precisely defined IgE glycovariants will be subjected to biochemical and biophysical characterization enabling the determination of structural integrity of the antibodies. As series of cell based assays will finally elucidate the impact of glycosylation to the function of IgE antibodies. These experiments will be carried out in cooperation with renowned immunologists/allergists (Prof. Rudolf Valenta, AKH Wien und Sophia Karagiannis, Kings College, London). We expect that the results will significantly contribute to a better understanding of molecular mechanisms driving the synthesis of complex protein glycosylation and to generate novel insights into IgE glycan biology. The knowledge might be transferred to other immunoglobulins and/or the generation of therapeutic IgE with optimized or novel functions.

IAntibodies (Abs) are critical components of the human immune system. They circulate as so called glycoproteins in the serum, referring to an important protein modification, namely the attachment of sugar residues (glycans) to the protein backbone. There has been mounting evidence favouring the role of glycans in the modulation of Ab activities. However, a broader understanding is lacking mainly due to inability to generate antibodies with defined glycan structures. In the present study, we focused on the production of IgE antibodies, an antibody class that is mainly involved in allergies. In order to study sugar-induced activities, it is first necessary to generate them in a homogeneous form, since there are a variety of structures. That was the first big challenge. A biotechnological approach developed by the project manager was used, which enables great flexibility when "engineering" sugar structures and IgE has actually been successfully produced with precisely defined glycosylation profiles. This was an important achievement for the next step, namely functional experiments. For this purpose, the two main activities, namely binding to specific antigens and the subsequent interaction with cellular receptors, were examined. While antigen binding is independent of IgE glycosylation, there is sugar-dependent interaction with cellular receptors. Our results indicate that IgEs control their activities through the glycosylation pattern. However, further experiments are needed to better understand the biological consequences and then potentially use them therapeutically.