Bacterial modulation of host glycosylation - in infection, biotechnology, and therapy

Abstract: A majority of the proteins of the immune system are glycosylated and the glycans of IgG are essential for its functionality. Bacteria display enzymes that modulate the glycans of the immune system to weaken the host defense and favor bacterial survival. In this thesis we aimed at exploring bacterial modulation of host glycosylation in infection and to evaluate the usefulness of bacterial enzymes in biotechnology and for therapeutic use. The role of IgG endoglycosidase EndoS in streptococcal virulence was evaluated in a murine model of invasive infection and we found significant contribution when heterologously expressed. We also discovered and characterized EndoS2, a novel enzyme specific and conserved in serotype M49 of streptococci, with enzymatic activity on the glycans of IgG and ?1-acid glycoprotein. Enterococcal pathogenesis was studied, and we found that the endoglycosidase EndoE cleaved glycans of lactoferrin to reduce the antibacterial functions and to support bacterial growth. A glycoform specificity difference between EndoS and EndoS2 was observed, and we suggested a method for quantification of high-mannose glycans on therapeutic antibodies, a key quality attribute. Finally, we explored the importance of Fc glycosylation of IgE and showed that EndoS cleaved glycans of this immunoglobulin causing a reduction of the immune cell activation in vivo, a potential new therapeutic strategy for severe IgE mediated allergies. In this thesis we demonstrate that glycans are an integral part of the immune system, and that the study of bacterial effectors of glycosylation paves the way for a deeper understanding of infections, for novel tools supporting the biotech arena, and for new therapeutic strategies.