Use this URL to cite or link to this record in EThOS:
Title: Mechanisms of immunoglobulin deactivation by Streptococcus pyogenes
Author: Dixon, Emma Victoria
ISNI:       0000 0004 5915 6210
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Restricted access.
Access from Institution:
The bacteria Streptococcus pyogenes produces a multitude of proteins which interact with and alter the functions of the host immune system. Two such proteins, Endoglycosidase S (EndoS) and Immunoglobulin G-degrading enzyme from S. pyogenes (IdeS) are able to specifically alter the effector functions of immunoglobulin G (IgG). EndoS is a glycoside hydrolase which removes the conserved N-linked glycan from IgG Fc whereas IdeS is a cysteine protease that cleaves the exible protein hinge of IgG. The activity of both proteins results in the reduced ability of IgG to elicit immune responses through Fc receptor binding and complement activation. Amongst other applications, both EndoS and IdeS are actively being explored as new therapeutics for IgG-mediated autoimmune diseases. Given the therapeutic potential of EndoS and IdeS, experiments were designed to investigate the structural and functional characteristics of these enzymes in an effort to understand their specficity for and activity against IgG. Here, bioinformatic and biophysical characterisation of EndoS identified subdomains outside of the catalytic domain which contribute to glycoside hydrolase activity. The substrate specificity of EndoS was also explored and showed that EndoS hydrolyses a broad range of glycans from the IgG scaffold. EndoS was also shown to have activity against alternative glycoprotein substrates, however, this non-specific activity was negligible in the context of whole serum. The effect of EndoS-mediated deglycosylation on the structure of the IgG Fc domain was explored using both X-ray crystallography and small-angle X-ray scattering. Small angle X-ray scattering was also used to characterise both EndoS and IdeS in complex with IgG Fc. Solution-state models of each complex were produced providing preliminary data towards how these enzymes interact with IgG. Overall, the results presented here contribute to our understanding of these enzymes which is of importance as they go forward into clinical applications.
Supervisor: Zitzmann, Nicole Sponsor: Wellcome Trust ; Clarendon Fund ; William Georgetti Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Life Sciences ; Biochemistry ; Glycobiology ; Molecular biophysics (biochemistry) ; Infectious diseases ; Immunology ; NMR spectroscopy ; Protein chemistry ; Enzymes ; Crystallography ; Biophysics ; Mass spectrometry ; Streptococcus pyogenes ; structural biology ; EndoS ; IdeS ; IgG ; antibodies