Single Molecule Förster Resonance Energy Transfer Studies of the Effect of Deglycosylation on the Structure of Immunoglobulin G

Abstract

The deglycosylation of immunoglobulin G (IgG) antibodies with the bacterial enzyme EndoS has been suggested as a potential treatment for some autoimmune disorders as this process leads to a diminished immune response. The reduction in immune response is thought to arise from weakened binding of effector molecules to the fragment crystallizable (Fc) region of IgG antibodies as a result of a conformational change in the Fc region. The nature of this structural alteration is uncertain due to conflicting results obtained from x-ray crystallography and small-angle x-ray scattering studies. To further examine the impact of deglycosylation on the structure of the Fc region, we have examined both glycosylated and EndoS deglycosylated IgG antibodies using single molecule Forster Resonance Energy Transfer (smFRET). The FRET efficiency histograms obtained from studying freely-diffusing, dye-labeled antibodies suggest that the flexibility of the Fc region increases upon deglycosylation.