Glycosylation of human IgG-Fc: influences on structure revealed by differential scanning micro-calorimetry.

Glycosylation of the Fc region of IgG (IgG-Fc) is essential for the full expression of Fc effector functions. The profound differences in functional activity observed between glycosylated and aglycosylated IgG have not previously been paralleled by the demonstration of large-scale structural changes. In the present study differential scanning microcalorimetry (DSMC) was used to investigate IgG-Fc glycoprotein stability and to determine the thermodynamic parameters for thermal unfolding, which will include a contribution from the intra-molecular oligosaccharide-protein interactions. The thermogram obtained for glycosylated IgG1-Fc yielded two clearly defined transitions whilst the glycosylated IgG4-Fc exhibited a single transition. The methodology was also able to reveal measurable differences in the stability of IgG4-Fc glycoforms differing by the presence or absence of terminal galactose residues; deglycosylated IgG4-Fc exhibited two transitions with evidence for destabilisation of the C(H)2 domain.